A population of mitochondrion-rich cells in the pars recta of mouse kidney.

Following perfusion of adult mouse kidney with a solution of nitroblue tetrazolium (NBT), certain epithelial cells in the pars recta (S3) segments of proximal tubules react to form cytoplasmic deposits of blue diformazan particles. Such cells are characterized by dark cytoplasm, small and often elliptical nuclei, elaborate, process-bearing profiles, and abundant mitochondria. The atypical epithelial cells display the additional characteristic of immunoreactivity for a wide spectrum of antigens, including mesenchymal proteins such as vimentin. Though present in kidneys of untreated or sham-operated animals, they are particularly evident under experimental conditions such as unilateral ureteral obstruction (UUO), appearing in both contralateral and obstructed kidneys over the course of a week's duration, but disappearing from the obstructed kidney as it undergoes the profound atrophy attributable to deterioration of the population of its proximal tubules. The cells do not appear in neonatal kidneys, even those undergoing UUO, but begin to be recognizable soon after weaning (28 days). It is possible that diformazan-positive cells in the mouse S3 tubular segment constitute a resident population of cells that can replenish or augment the tubule. Although somewhat similar cells, with dark cytoplasm and vimentin expression, have been described in human, rat, and transgenic mouse kidney (Smeets et al. in J Pathol 229: 645-659, 2013; Berger et al. in Proc Natl Acad Sci U S A 111: 1533-1538, 2014), those cells-known as "scattered tubule cells" or "proximal tubule rare cells"- differ from the S3-specific cells in that they are present throughout the entire proximal tubule, often lack a brush border, and have only a few mitochondria.

Glomerulotubular disconnection in neonatal mice after relief of partial ureteral obstruction.

Ureteropelvic junction obstruction is a common cause of congenital obstructive nephropathy. To study the pathogenesis of nephropathy, a variable-partial, complete or a sham unilateral ureteral obstruction (UUO) was produced in mice within 2 days of birth. The obstruction was released in some animals at 7 days and kidneys harvested at 7-42 days of age for histologic and morphometric study. Renal parenchymal growth was stunted by partial UUO with the impairment proportional to the duration and severity of obstruction. Proximal tubule apoptosis and glomerulotubular disconnection led to nephron loss. Relief of partial UUO arrested glomerulotubular disconnection, resolved tubule atrophy, and interstitial fibrosis with remodeling of the renal architecture. Relief of severe UUO did not result in recovery. Compensatory growth of the contralateral kidney depended on the severity of obstruction. Our studies indicate that relief of moderate UUO will minimize nephron loss. Application of this technique to mutant mice will help develop future therapies to enhance nephron recovery.

Osteopontin regulates renal apoptosis and interstitial fibrosis in neonatal chronic unilateral ureteral obstruction.

Congenital obstructive nephropathy is a major cause of renal insufficiency in children. Osteopontin (OPN) is a phosphoprotein produced by the kidney that mediates cell adhesion and migration. We investigated the role of OPN in the renal response to unilateral ureteral obstruction (UUO) in neonatal mice. OPN null mutant (-/-) and wild-type (+/+) mice were subjected to sham operation or UUO within the first 2 days of life. At 7 and 21 days of age, fibroblasts (fibroblast-specific protein (FSP)-1), myofibroblasts (alpha-smooth muscle actin (SMA)), and macrophages (F4/80) were identified by immunohistochemical staining. Apoptotic cells were detected by terminal deoxy transferase uridine triphosphate nick end-labeling technique and interstitial collagen by Masson trichrome or picrosirius red stain. Compared to sham-operated or contralateral kidneys, obstructed kidneys showed increases in all parameters by 7 days, with further increases by 21 days. After 21 days UUO, there was an increase in tubular and interstitial apoptosis in OPN -/- mice as compared to +/+ animals (P<0.05). However, FSP-1- and alpha-SMA-positive cells and collagen in the obstructed kidney were decreased in OPN -/- compared to +/+ mice (P<0.05), whereas the interstitial macrophage population did not differ between groups. We conclude that OPN plays a significant role in the recruitment and activation of interstitial fibroblasts to myofibroblasts in the progression of interstitial fibrosis in the developing hydronephrotic kidney. However, OPN also suppresses apoptosis. Future approaches to limit the progression of obstructive nephropathy in the developing kidney will require targeting of specific renal compartments.

Formation, transformation and transport of black carbon (charcoal) in terrestrial and aquatic ecosystems.

Black carbon (BC) is ubiquitous in terrestrial environments and its unique physical and chemical properties suggest that it may play an important role in the global carbon budget (GCB). A critical issue is whether the global production of BC results in significant amounts of carbon (C) being removed from the short-term bio-atmospheric carbon cycle and transferred to the long-term geological carbon cycle. Several dozen field and laboratory based studies of BC formation during the burning of biomass have been documented. Findings are difficult to interpret because they have been expressed in an inconsistent manner, and because different physical and chemical methods have been used to derive them. High error terms documented in many of these studies also highlight the problems associated with the quantification of the amount of biomass C consumed in fire, the amount of residue produced and the constituents of that residue. To be able to estimate the potential for BC as a carbon sink, issues regarding its definition, the methods used in its identification and measurement, and the way it is expressed in relation to other components of the carbon cycle need to be addressed. This paper presents BC data in a standard way; BC production as a percentage of the amount of C consumed by fire (BC/CC), which can be readily integrated into a larger carbon budget. Results from previous studies and new data from Australian ecosystems were recalculated in this way. As part of this process, several BC estimates derived solely from physical methods were discarded, based on their inability to accurately identify and quantify the BC component of the post-fire residue. Instead, more focus was placed on BC estimates obtained by chemical methods. This recalculated data lowered the estimate for BC formation in forest fires from 4% to 5% to <3% BC/CC. For savannah and grassland fires a value of <3% is consistent with reported data, but considerable variation among estimates remains. An updated flow-chart linking the sources, fluxes and pools of BC formed in the terrestrial environment with the aquatic and marine environments, and estimates of mean residence times for BC are also presented.

Abeta(1-42) and aluminum induce stress in the endoplasmic reticulum in rabbit hippocampus, involving nuclear translocation of gadd 153 and NF-kappaB.

Apoptosis may represent a prominent form of neuronal death in chronic neurodegenerative disorders, such as Alzheimer's disease. Although apoptosis under mitochondrial control has received considerable attention, mechanisms used within the endoplasmic reticulum (ER) and nucleus in mediating apoptotic signals are not well understood. A growing body of evidence is emerging from different studies which suggests an active role for the ER in regulating apoptosis. Disturbances of ER function have been shown to trigger two different apoptotic pathways; one involves cross-talk with mitochondria and is regulated by the antiapoptotic Bcl-2, and the second is characterized by the activation of caspase-12. Also, stress in the ER has been suggested to result in the activation of a number of proteins, such as gadd 153 and NF-kappa, and in the downregulation of the antiapoptotic protein, Bcl-2. In the present study, the intracisternal injection in aged rabbits of either the neurotoxin aluminum maltolate or of Abeta(1-42), has been found to induce nuclear translocation of gadd 153 and the inducible transcription factor, NF-kappaB. Translocation of these two proteins is accompanied by decreased levels of Bcl-2 in both the ER and the nucleus. Aluminum maltolate, but not Abeta, induces caspase-12 activation which is a mediator of ER-specific apoptosis; this is the first report of the in vivo activation of caspase-12. These findings indicate that the ER may play a role in regulating apoptosis in vivo, and could be of significance in the pathology of neurodegeneration and related disorders.

GDNF protects against aluminum-induced apoptosis in rabbits by upregulating Bcl-2 and Bcl-XL and inhibiting mitochondrial Bax translocation.

Direct (intracisternal) injection of aluminum complexes into rabbit brain results in a number of similarities with the neuropathological and biochemical changes observed in Alzheimer's disease and provides the opportunity to assess early events in neurodegeneration. This mode of administration induces cytochrome c release from mitochondria, a decrease in Bcl-2 in both mitochondria and endoplasmic reticulum, Bax translocation into mitochondria, activation of caspase-3, and DNA fragmentation. Coadministration of glial cell neuronal-derived factor (GDNF) inhibits these Bcl-2 and Bax changes, upregulates Bcl-XL, and abolishes the caspase-3 activity. Furthermore, treatment with GDNF dramatically inhibits apoptosis, as assessed by the TUNEL technique for detecting DNA damage. Treatment with GDNF may represent a therapeutic strategy to reverse the neuronal death associated with Alzheimer's disease and may exert its effect on apoptosis-regulatory proteins.

Co-involvement of mitochondria and endoplasmic reticulum in regulation of apoptosis: changes in cytochrome c, Bcl-2 and Bax in the hippocampus of aluminum-treated rabbits.

Neurodegenerative diseases, including Alzheimer's disease, are characterized by a progressive and selective loss of neurons. Apoptosis under mitochondrial control has been implicated in this neuronal death process, involving the release of cytochrome c into the cytoplasm and initiation of the apoptosis cascade. However, a growing body of evidence suggests an active role for the endoplasmic reticulum in regulating apoptosis, either independent of mitochondrial, or in concert with mitochondrial-initiated pathways. Members of the Bcl-2 family of proteins have been shown to either inhibit apoptosis, as is the case with Bcl-2, or to promote it, in the case of Bax. Investigations in our laboratory have focused on neuronal injury resulting from the intracisternal administration of aluminum maltolate to New Zealand white rabbits, an animal system relevant to a study of human disease in that it reflects many of the histological and biochemical changes associated with Alzheimer's disease. Here we report that treatment of young adult rabbits with aluminum maltolate induces both cytochrome c translocation into brain cytosol, and caspase-3 activation. Furthermore, as assessed by Western blot analysis, these effects are accompanied by a decrease in Bcl-2 and an increase in Bax reactivity in the endoplasmic reticulum.

The neuronal organization of the supracapsular part of the stria terminalis in the rat: the dorsal component of the extended amygdala.

In the present normal anatomical light and electron microscopic study in the rat, histochemical (Nissl, Timm, Golgi) or immunocytochemical (microtubule-associated protein type 2, glutamate decarboxylase, glutamate receptor subunit 1, synaptophysin) stains were used to analyse neurons embedded within the stria terminalis and their associated neuropil. These cells are closely related to the bed nucleus of the stria terminalis and the centromedial amygdala, and have been termed the "supracapsular part of the bed nucleus of the stria terminalis". The largest part of this neuronal complex is located in the ventrolateral part of the stria, where it appears as a round or oval "lateral pocket" in virtually any type of light microscopic preparation because of its collection of neuronal cell bodies and dense neuropil, in addition to a lacework of unmyelinated axons. A much smaller but still distinct "medial pocket" is located in the medial corner of the stria. The large lateral subdivision of the supracapsular stria terminalis is directly continuous with the lateral bed nucleus of the stria terminalis and extends to the central amygdaloid nucleus, containing a column of neurons that is only broken up into cell clusters at the most caudal levels of the stria as it drops vertically toward the amygdala. The considerably smaller medial subdivision appears, in turn, to be directly continuous with the medial part of the bed nucleus of the stria terminalis. The medial column tapers off more rapidly than the lateral part, so that as the middle levels are approached, only small interrupted clusters of cells are seen. Solitary neurons can also be found in practically every part of the stria terminalis except among the ventrally located axons of the commissural component. Most of the neurons are small to medium in size, as viewed in transverse sections of the stria, but larger neurons are also encountered. In sections parallel to the stria, many neurons are fusiform in appearance. The dendrites are often aligned in a longitudinal fashion; many of the dendrites related to the cells in the lateral pocket are moderately to densely spined, whereas those in the medial pocket are more sparsely spined. The neuropil in both the lateral and medial pockets is characterized by boutons, bundles of unmyelinated axons, and dendrites. Based on their vesicle content, the boutons are divided into three major types: (A) round or slightly oval, agranular vesicles of uniform size; (B) pleomorphic, agranular vesicles, many of which are flattened; and (C) pleomorphic agranular vesicles, some of which are considerably larger than the ones in type B boutons. Type A boutons establish contacts with both dendritic spines and shafts, whereas types B and C usually contact dendritic shafts and sometimes somata. These synaptic components are similar to those described earlier for the central and medial amygdaloid nuclei. Overall, our results support the contention advanced in 1923 by Johnston [J. comp. Neurol. 35, 337481] that the cells accompanying the stria terminalis are interconnecting columns of a macrostructure encompassing the bed nucleus of the stria terminalis and centromedial amygdala. More recently, it has been appreciated that columns of neurons below the globus pallidus also belong to this macrostructure [Alheid G. F. et al. (1995) In The Rat Nervous System, 2nd edn, pp. 495 578, Academic, San Diego; de Olmos J. S. et al. (1985) In The Rat Nervous System, pp. 223-334, Academic, Sydney], which has been named the "extended amygdala".

Amygdaloid input to transiently tyrosine hydroxylase immunoreactive neurons in the bed nucleus of the stria terminalis of the rat.

Several studies have reported transient expression of tyrosine hydroxylase in a subpopulation of neurons in the bed nucleus of stria terminalis of preadolescent rats. The tyrosine hydroxylase immunoreactive (TH) neurons, which are of small to medium size and often display a typical bipolar configuration, are confined to the intermediate part of the lateral bed nucleus. By the use of a combination of experimental tracer techniques and immunocytochemical methods, we have demonstrated that these neurons receive a significant number of amygdaloid afferents, which establish mostly symmetric synaptic contacts on the cell bodies and sparsely spined dendritic shafts of the TH neurons. TH neurons also receive a small number of tyrosine hydroxylase-positive terminals of unspecified origin.

Change in endothelial cell morphology at arterial branch sites caused by a reduction of intramural stress.

Arterial branch sites have very high intramural stresses at physiologic intraluminal pressures; the same sites have a predilection for atherosclerosis. The effect of intramural stress on endothelial cell morphology was investigated. Five rabbits had permanent casts placed around a segment of the abdominal aorta-left renal artery branch area during controlled hypotension, thus reducing intramural stress without narrowing the lumen. These five animals, and three normal rabbits, were sacrificed after 4-8 weeks, and the vessels were perfused with buffered 2.5% glutaraldehyde for 2 h at 100 mm Hg pressure. The aortas were examined by scanning electron microscopy. In normal aortas, the distal region of the ostia of the left renal and celiac arteries just beyond the flow divider displayed many morphologically altered endothelial cells ranging from spindle shape to cobble-stone shape. The same aortic area of casted rabbits, as well as the straight abdominal aorta in all rabbits, showed a smooth surface of endothelial cells with intact cell borders and no morphologically altered cells. At branch sites, the occurrence of morphologically altered endothelial cells may be due to increased intramural stress. When intramural stress is reduced, the morphology of branch endothelial cells changes to resemble that of the unbranched regions. In conclusion, endothelial cell morphology changes in response to changes in intramural stress.

The atrial myocardial cells of mouse heart: a structural and stereological study.

Structural and stereological studies of mouse atrial myocardial cells, carried out in the same fashion as our previous investigations on mouse ventricle, demonstrate an extremely well-developed sarcoplasmic reticulum (SR) in atrial cells. The volume fraction (Vv) of the SR exceeds 12% in mouse atrial cells; perimyofibrillar network SR constitutes the major portion. We have confirmed the findings of Bossen et al. (1981, Tissue Cell 13, 71-77) of a difference between atria in terms of coupling density, the right atrium having a significantly lower incidence of interior junctional SR than the left. The SR of mouse atrium comprises a rich variety of specialized segments, including the IJSR, peripheral junctional SR, corbular SR, cisternal SR (including regions similar to fenestrated collars of striated skeletal muscle SR), as well as a peculiar form of extended junctional SR (EJSR). Although less frequent in occurrence than corbular SR, the EJSR seems closely related, since it occurs in multiple clusters at or near the Z-line regions, contains internal granular densities, and bears surface-connected structures resembling junctional processes. Seen in thin sections, mouse atrial EJSR elements are more complex than corbular SR, being larger in diameter and frequently circular in profile. Thick-section and serial-section analyses reveal that bodies of EJSR are in fact hollow spheroids. The transverse-axial tubular system of mouse atrium is rather poorly developed in comparison to its ventricular counterpart. The Golgi apparatus and associated specific atrial granules are prominent cell components. "Focal ellipsoidal deposits" (FEDs) previously described by Page and co-workers (1986, Amer. J. Physiol.) are consistently located adjacent to the Golgi region, but immunocytochemical staining for two different segments of atrial natriuretic peptide reveals no specific reaction in FEDs, whereas the SAGs are densely labeled for both antibodies.

Identification of individual renocortical cells that secrete renin.

Successful application of the reverse hemolytic plaque assay was developed to identify individual renocortical cells that secrete renin directly. The plaque assay was validated by a number of established criteria. Using this technique, we demonstrate an increase in renin secretion with beta-adrenergic stimulation and an inhibition of renin secretion with extracellular calcium in groups of renin-secreting cells. Transmission electron microscopy of the cell in the center of a hemolytic plaque demonstrated a modified vascular smooth muscle cell with densely packed secretory granules. Electron microscopy immunocytochemistry demonstrated the presence of renin in the secretory granules, confirming the identity of the cell as a renal juxtaglomerular cell. The technology developed here has allowed the precise identification and study of the individual renin-secreting juxtaglomerular cell.

Ultrastructure of the myocardium of the least shrew, Cryptotis parva Say.

The heart of the least shrew, Cryptotis parva Say, is an extremely active organ, capable of achieving rates of 800-1,200 beats/minute. The general features of myocardial cell ultrastructure in this insectivore are much like those of other small mammals; no single striking feature of fine structure is present to which the physiological properties of this heart might necessarily be attributed. Still there exist in these myocardial cells a number of atypical properties. These include 1) mitochondria having a wide variety of sizes and internal configurations 2) a pleiomorphic, highly ramified, small-diameter transverse-axial tubular system (TATS) 3) numerous "labyrinths," which are proliferated components of the TATS, and 4) myofibril-free regions, located both in juxtanuclear and other myoplasmic levels and populated by a concentration of TATS elements and fibrillar structures. Features (2) and (3) are also characteristic of another fast-beating heart, that of the mouse. The sinoatrial and atrioventricular nodal regions, as well as a Purkinje system, have been identified in the least shrew heart, along with sparsely distributed atrial cells whose myofibrils contain proliferated Z-band material. A feature frequently encountered in atrial working muscle cells is the occurrence of close appositions between gap junctions and tubules of sarcoplasmic reticulum; such appositions are also present in other regions of the shrew heart, as are complexes composed of gap junctions and mitochondria.

Membrane systems of guinea pig myocardium: ultrastructure and morphometric studies.

The structure and quantitative contribution of membrane systems (transverse-axial tubular system [TATS] and sarcoplasmic reticulum [SR]) have been investigated in the heart of the adult guinea pig. Although previous quantitative studies have been made of guinea pig myocardium, this is the first such study that has utilized tissue in which membrane system elements were clearly identified by selective staining (in this case by the osmium-ferrocyanide [OsFeCN] postfixation method). Both membrane systems are highly developed in ventricular cells, but a TATS is essentially absent from atrial myocytes. The ventricular TATS consists principally of large-bore elements which may be oriented transversely, axially, or obliquely, making numerous anastomoses with one another to form a highly interconnected system of extracellular spaces that penetrate to all myoplasmic depths of the ventricular cell. The cell coat that lines the lumina of these tubules is structured, containing fibrillar structures that run along the length of the tubule. The volume fraction (VV) of the ventricular TATS is low (2.5-3.2%), in consideration of the qualitative prominence of the TATS in these cells. The relative total population of sarcoplasmic reticulum is higher in the atria (VV of 10-11%) than in the ventricles (VV of ca. 8%). In all guinea pig myocytes, several major structural divisions of SR can be discerned, which include network SR, junctional SR, corbular SR, and cisternal SR. Junctional SR (J-SR) in the atrial cells is limited almost exclusively to peripheral saccules of junctional SR (PJSR), whereas both interior J-SR and PJSR are present in the ventricle. Two distinct morphological types of PJSR appear in atrial cells, including both flattened and distended saccules, the latter resembling PJSR of lower vertebrate heart. Spheroidal bodies of SR with opaque contents (corbular SR) are prominent at or near Z-line levels of the sarcomeres of atrial and ventricular cells. Cisternal SR is likely a subset of network SR, but some examples appear related to rough endoplasmic reticulum. An overall impression obtained from this study is that guinea pig atria are composed of structurally primitive cells, whereas the ventricular cardiac muscle cells are more highly developed entities.

6-Mercaptopurine treatment affects the membrane potentials of rat skeletal muscle fibers.

6-Mercaptopurine (6-MP) was injected daily (2 mg/kg sc) into 24 Sprague-Dawley rats during the first three weeks of life. There were 23 saline-injected control animals. Atrophy of the muscles of the hindquarters in the 6-MP-treated rats began at about 4 months of age. The membrane potentials (Em) of the isolated extensor digitorum longus (EDL) and the caudofemoralis (CF) muscle (in situ) were measured with intracellular microelectrodes at 6-18 months of age. It was found that there was a wide spectrum of fibers with respect to electrical abnormalities in the 6-MP-treated muscles, some fibers having perfectly normal parameters. However, the mean resting Em of fibers in the EDL muscle of 6-MP-treated rats (-61.1 +/- 0.7 mV) was lower than that of the control rats (-69.7 +/- 0.6 mV). The same was true for the fibers of the CF muscle (-64.9 +/- 1.5 mV for 6-MP-treated fibers vs -71.6 +/- 1.3 mV for controls). Experiments done in the presence and absence of ouabain indicated that the contribution of the electrogenic pump potential to Em was similar in 6-MP-treated and control rats, and therefore could not account for the depolarization observed in 6-MP-treated rats. The data also demonstrated that this depolarization was not due to a decreased intracellular K+ concentration. The Na+/K+ permeability ratio (PNa/PK) was higher in the 6-MP-treated rats, and could account for the decreased resting Em. The APs of 6-MP-treated rats (elicited from the natural Em of the fiber) had more fibers with a lower maximum rate of rise (+Vmax) (330 +/- 20 vs 391 +/- 17 V/sec) and lower amplitude (65.1 +/- 2.9 vs 73.3 +/- 1.8 mV) than in the control muscles. When hyperpolarized to -90 mV before eliciting the AP, fibers from 6-MP-treated rats still displayed depressed AP rates of rise (+Vmax of 382 +/- 19 vs 511 +/- 21 V/sec in controls), depressed AP amplitudes (97 +/- 2.1 vs 105 +/- 1.6 mV in controls) and slightly prolonged duration at 50% amplitude (APD50) (0.66 +/- 0.03 vs 0.60 +/- 0.02 sec in controls). These electrophysiological alterations produced by this chemically-induced myopathy are similar to those observed in murine muscular dystrophy.

The sarcoplasmic reticulum of mouse heart: its divisions, configurations, and distribution.

The sarcoplasmic reticulum (SR) is a prominent, highly ramified component of mouse myocardial cells. The use of ferrocyanide-reduced osmium tetroxide (OsFeCN) as a postfixative solution facilitates appreciation of both its extent and three-dimensional architecture. We have found that the individual volume fractions (Vv) of myofibrils, mitochondria, and SR are similar in cells of the right and left ventricular walls. Vv(total SR) is approximately 7%, a value considerably larger than previously reported. We attribute this disparity in large part to the recognition factor which comes into play with OsFeCN-treated tissue. Previous observations pertaining to the stereology of myocardial SR have likely substantially underestimated both volume fraction and surface density of this membrane system, since none to this point has utilized specific staining such as that conferred by the OsFeCN regimen. Our stereological measurements of different depths of the ventricular cell indicate that although considerable differences are found between SR configuration at peripheral and deep cell levels, no significant difference exists between the volume fractions of either the total SR or its individual constituents. Two different stereologic regimens gave close agreement on volume fractions of the various SR segments; the majority (approximately 92%) of the total SR is network SR, whereas the remainder is composed of the various categories of junctional SR (peripheral, apposed to the surface sarcolemma; interior, complexed with the transverse-axial tubular system; corbular, existing free of sarcolemmal contact). In the adult mouse, interior junctional SR greatly preponderates the other types of junctional SR; corbular SR is qualitively assessed to be a far more common component of atrial cells than of ventricular cardiomyocytes.

Effects of 6-mercaptopurine treatment on the membrane potentials of rat skeletal muscle fibers.

6-Mercaptopurine (6-MP), injected daily (2 mg/kg s.c.) into Sprague-Dawley rats during the first 3 weeks of life, causes atrophy in muscles of the hindquarters beginning at 4 months of age. The extensor digitorium longus (EDL) muscles from 24 rats injected with 6-MP and 23 saline-injected controls, 6-18 months of age, were studied. Electron microscopy showed a number of abnormalities in the EDL muscle of 6-MP-treated rats, such as myocytes with atypical ultrastructure (including disorganized myofibrils) adjacent to structurally normal cells. Membrane potentials (Em) were measured in the isolated EDL and in the caudofemoralis (CF) muscle in situ. The mean Em of fibers in the EDL of 6-MP-treated rats (-61.1 +/- 0.7 (SE) mV) was lower than that of the control rats (-69.7 +/- 0.6 mV). The same was true for the fibers of the CF muscle (-64.9 +/- 1.5 mV for 6-MP-treated fibers vs. -71.6 +/- 1.3 mV for controls). The contribution of the electrogenic pump potential to Em (+/- ouabain) was similar in 6-MP-treated and control rats, and therefore could not account for the depolarization observed in 6-MP-treated rats. This depolarization was not due to a decreased intracellular K+ concentration. The Na+:K+ permeability ratio (PNa/PK) was higher in the 6-MP-treated rats and could account for the decrease in Em.(ABSTRACT TRUNCATED AT 250 WORDS)

Intercalated discs of mammalian heart: a review of structure and function.

Intercalated discs are exceptionally complex entities, and possess considerable functional significance in terms of the workings of the myocardium. Examination of different species and heart regions indicates that the original histological term has become out-moded; it is likely, however, that all such complexes will continue to fall under the generic heading of 'intercalated discs'. The membranes of the intercalated discs establish specific associations with a variety of intracellular and extracellular structures, as well as with numerous types of proteins and glycoproteins. Characterization of discs and their components has already brought together a large number of research disciplines, including microscopy, cytochemistry, morphometry, cell isolation and culture, cell fractionation, cryogenics, immunology, biochemistry, and electrophysiology. The continued dissection of substance and function of intercalated discs will depend on such interdisciplinary approaches. The intercalated disc component which continues to attract the greatest amount of interest is the so-called gap junction. All indications thus far point to a great deal of inherent lability in the architecture of the gap junction. There is thus considerable potential for the creation of artefact while preserving and observing gap junctions, and this problem will doubtless continue to hamper the understanding of their functions. A question of special interest concerns whether the gap junctions of intercalated discs are required for transfer of electrical excitation between cells, or maintain cell-to-cell adhesion, or in fact subserve both electrical and structural phenomena. Two schools of thought exist with respect to cell-to-cell coupling in the heart. One proposes that low-resistance junctions in the discs mediate electrical coupling, whereas the other supports the possibility of coupling across ordinary high-resistance membranes. Thus the intercalated discs continue to be a source of controversy, just as they have been since they were originally discovered in heart muscle over a century ago.

Occurrence of intramitochondrial Ca2+ granules in a hypertrophied heart exposed to adriamycin.

Left ventricular hypertrophy was produced in rabbits by narrowing the abdominal aorta in the subdiaphragmatic region. Six weeks after the surgery, sham control as well as hypertrophied animals were treated with adriamycin. Myocardial cell damage resulting from a total cumulative dose of 5 mg/kg of adriamycin was seen only in hypertrophied hearts. Alterations in muscle cells of these hearts included prominent "contraction bands" and perinuclear edema. Mitochondria were characterized by swelling and accumulation of electron-opaque granules. Energy-dispersive x-ray analysis of the mitochondria revealed the presence of calcium in these granules. The study confirms that the hypertrophied heart is more vulnerable to adriamycin-induced cell damage and this may be due to an increased susceptibility of these hearts to the occurrence of Ca2+ overload in the cell.