Local control of oligodendrocyte development in isolated dorsal mouse spinal cord.

The earliest oligodendrocyte precursors have been proposed to arise in the ventral ventricular zone of the embryonic thoraco-lumbar spinal cord and subsequently migrate to populate dorsal spinal cord. Using the expression of O4 immunoreactivity to define cells of the oligodendrocyte lineage, the development of oligodendrocytes in different regions of the mouse spinal cord was assayed. Consistent with earlier studies in other species, isolated explants of E11 ventral but not dorsal mouse spinal cord developed oligodendrocytes after 7 days in vitro. In contrast, in cultures derived from E13 embryos O4(+) oligodendrocytes developed in both ventral and dorsal cultures after 5 days in vitro. These data are consistent with a ventral to dorsal migration of committed oligodendrocyte progenitors occurring between E11 and E13. Although isolated early embryonic dorsal spinal cord does not give rise to oligodendrocytes in short term cultures, in long term cultures O4(+) cells develop in a subset of dorsal explants. After 10 days in vitro approximately 25% of both cervical and thoraco-lumbar E11 derived dorsal explants contained significant numbers of O4(+) cells. The molecular requirements for the dorsally-derived oligodendrocytes was similar to that in ventral cord. The appearance of O4(+) cells was dependent on sonic hedgehog and enhanced by neuregulin. These data suggest that early embryonic dorsal mouse spinal cord has an independent potential to generate oligodendrocytes under appropriate conditions. Whether this potential is realized during normal spinal cord development is currently unknown.

Protein kinase C regulation of p-glycoprotein-mediated xenobiotic secretion in renal proximal tubule.

Fluorescence microscopy, fluorescent substrates [daunomycin and a fluorescent cyclosporin A (CSA) derivative] and digital image analysis were used to examine the role of protein kinase C (PKC) in the control of p-glycoprotein in killifish renal proximal tubules. PKC activators, phorbol ester (phorbol 12-myristate 13-acetate, PMA) and dioctylglycerol, reduced luminal drug accumulation, and protein kinase inhibitors, staurosporine and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), increased luminal accumulation; a PMA analog that does not activate PKC was without effect. PMA effects were blocked by staurosporine. The increase in luminal fluorescence caused by staurosporine was blocked by the p-glycoprotein substrate, CSA, indicating that this component of transport was indeed mediated by p-glycoprotein. Neither PMA, dioctylglycerol, nor protein kinase inhibitors altered cellular drug accumulation. Finally, in primary cultures of flounder proximal tubule cells, PMA decreased transepithelial [3H]daunomycin secretion. This pharmacological approach demonstrates that in teleost renal proximal tubule, p-glycoprotein-mediated xenobiotic secretion is negatively correlated with changes in PKC activity, a finding that conflicts with results from studies using mammalian tumor cells that express p-glycoprotein.

Heat shock-induced protection and enhancement of Na+-glucose cotransport by LLC-PK1 monolayers.

Monolayers of the porcine-derived renal epithelial cell line, LLC-PK1, were used to characterize the effects of heat stress on Na+-glucose cotransport. Transepithelial current dependent on 5 mM glucose (I(Glc)), phloridzin-sensitive current (I(phz)), and total transepithelial current (I(total)) were measured as indicators of Na+-glucose cotransport. Severe heat shock (SHS; 45 degrees C for 1 h, then 37 degrees C for measurements) decreased transepithelial electrical resistance (TER), I(Glc), I(phz), and I(total) 50-70%. Mild heat shock (MHS; 42 degrees C for 3 h, then 37 degrees C for 12 h) induced accumulation of 72-kDa heat shock protein (HSP-72), decreased damage to TER from SHS, and prevented damage to I(Glc), I(phz), and I(total). Kinetic analysis showed that SHS damaged and MHS protected total Na+-glucose transport capacity (Vmax of I(Glc)). MHS alone increased TER (50%), I(Glc) (20%), I(total) (20%), and Vmax of I(Glc) (25%). On enhancement of the Na+ gradient by depletion of intracellular Na+, MHS increased I(Glc) 50% and had no effect on transepithelial Na+-dependent sulfate reabsorptive flux measured concurrently or in Na+-replete tissues. These effects of MHS were not reflected in effects on cell survival or luminal membrane surface area as indicated by lactate dehydrogenase or alkaline phosphatase release. In conclusion, HSP-72-inducing heat treatment both protected and enhanced Na+-glucose cotransport independently of the luminal membrane Na+ gradient and selectively with respect to effects on TER, reabsorptive sulfate transport, cell survival, and luminal membrane surface area.

Increased pro-opiomelanocortin-derived peptide release in myotonic dystrophy.

The response of plasma immunoreactive (IR)-ACTH, IR-beta-endorphin (beta-END) and IR-cortisol to insulin-induced hypoglycaemia, an acute stimulus to the pituitary corticotrophs through the central nervous system, and to synthetic ovine corticotrophin-releasing hormone (CRH), a direct corticotroph stimulator, were studied in normal males and males with myotonic dystrophy. Myotonics had an increased IR-ACTH and IR-beta-END response to hypoglycaemia and an increased IR-ACTH response to CRH compared with normals. Plasma IR-cortisol response were not different in either group of subjects to both stimuli. This neuroendocrine abnormality in myotonic dystrophy may represent a manifestation of the purported specific cell membrane defect underlying the disease. This is the first report of an abnormality in proopiomelanocortin peptide release in myotonic dystrophy.

Renin exists in human adrenal tissue.

Readily detectable levels of renin activity were demonstrated in human adrenal tissues. This activity was inhibited by specific antibody raised against pure renin, indicating that it was not due to the nonspecific action of proteases. The renin activity was predominantly in the cortex rather than in the medulla of the adrenal. An adrenal gland that was surgically removed from a patient with Cushing's disease and had high renin activity was used for further characterization of the enzyme. It shared many biochemical features with kidney renin, such as molecular weight, isoelectric point, glycoprotein nature, optimum pH of enzyme activity, affinity to pepstatin, and the presence of trypsin-activatable inactive renin. The lack of correlation between PRA and the adrenal renin, and the particulate localization of the subcellular distribution of adrenal renin suggested its local origin rather than contamination or contribution of the plasma enzyme.

Circulating levels of angiotensin I measured by radioimmunoassay in hypertensive subjects.

The development of a uniquely sensitive and specific antiserum to AI has led to the establishment of a radioimmunoassay capable of detecting 7.5 pg of AI per milliliter of plasma. Due to its sensitivity this assay permits the measurement of circulating levels of AI, obviating many of the controversial aspects of previously described AI assays which all required either an incubation step at 37 degrees C to allow renin to catalyze the formation of sufficient AI or an extraction procedure to concentrate sufficient peptide to make quantification feasible. Since the sensitivity of this assay also depends upon the availability of very pure trace, a method is described for preparing monoiodinated 125I-AI of specific activity greater than 1000 microCi/microgram. To demonstrate the versatility and sensitivity of this assay, changes in circulating AI levels in response to physiologic stimuli were measured. Blood samples were obtained from 88 subjects from the inferior vena cava below the renal veins in both the supine and upright positions. Values ranged from 12 to 1990 pg/ml of plasma. Eighty-five of the 88 displayed a rise in the AI level during an upright tilt, the mean for the group increasing from 220 to 385 pg/ml of plasma. Three subjects had samples drawn simultaneously from the inferior vena cava and a peripheral artery and/or vein. The amounts of AI in all three sampling locations were essentially the same. Seventeen patients with essential hypertension underwent an infusion of 1.5 L of normal saline, and circulating AI levels were determined before and 120 and 150 min after the start of the infusion. All 17 experienced suppression of their AI levels, the mean for the group at 0, 120 and 150 min being 177, 55, and 50 pg/ml of plasma, respectively. Circulating AI correlated well (r = 0.87009) with plasma renin activity in 226 samples from the renal veins and inferior vena cava from individuals with hypertension of various etiologies.