The α2 isoform Na,K-ATPase modulates contraction of rat mesenteric small artery via cSrc-dependent Ca2+ sensitization.

AIMS: The Na,K-ATPase is involved in a large number of regulatory activities including cSrc-dependent signalling. Upon inhibition of the Na,K-ATPase with ouabain, cSrc activation is shown to occur in many cell types. This study tests the hypothesis that acute potentiation of agonist-induced contraction by ouabain is mediated through Na,K-ATPase-cSrc signalling-dependent sensitization of vascular smooth muscle cells to Ca2+ . METHODS: Agonist-induced rat mesenteric small artery contraction was examined in vitro under isometric conditions and in vivo in anaesthetized rats. Arterial wall tension and [Ca2+ ]i in vascular smooth muscle cells were measured simultaneously. Changes in cSrc and myosin phosphatase targeting protein 1 (MYPT1) phosphorylation were analysed by Western blot. Protein expression was examined with immunohistochemistry. The α1 and α2 isoforms of the Na,K-ATPase were transiently downregulated by siRNA transfection in vivo. RESULTS: Ten micromolar ouabain, but not digoxin, potentiated contraction to noradrenaline. This effect was not endothelium-dependent. Ouabain sensitized smooth muscle cells to Ca2+ , and this was associated with increased phosphorylation of cSrc and MYPT1. Inhibition of tyrosine kinase by genistein, PP2 or pNaKtide abolished the potentiating effect of ouabain on arterial contraction and Ca2+ sensitization. Downregulation of the Na,K-ATPase α2 isoform made arterial contraction insensitive to ouabain and tyrosine kinase inhibition. CONCLUSION: Data suggest that micromolar ouabain potentiates agonist-induced contraction of rat mesenteric small artery via Na,K-ATPase-dependent cSrc activation, which increases Ca2+ sensitization of vascular smooth muscle cells by MYPT1 phosphorylation. This mechanism may be critical for acute control of vascular tone.

The giraffe kidney tolerates high arterial blood pressure by high renal interstitial pressure and low glomerular filtration rate.

BACKGROUND: The tallest animal on earth, the giraffe (Giraffa camelopardalis) is endowed with a mean arterial blood pressure (MAP) twice that of other mammals. The kidneys reside at heart level and show no sign of hypertension-related damage. We hypothesized that a species-specific evolutionary adaption in the giraffe kidney allows normal for size renal haemodynamics and glomerular filtration rate (GFR) despite a MAP double that of other mammals. METHODS: Fourteen anaesthetized giraffes were instrumented with vascular and bladder catheters to measure glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). Renal interstitial hydrostatic pressure (RIHP) was assessed by inserting a needle into the medullary parenchyma. Doppler ultrasound measurements provided renal artery resistive index (RI). Hormone concentrations as well as biomechanical, structural and histological characteristics of vascular and renal tissues were determined. RESULTS: GFR averaged 342 ± 99 mL min(-1) and ERPF 1252 ± 305 mL min(-1) . RIHP varied between 45 and 140 mmHg. Renal pelvic pressure was 39 ± 2 mmHg and renal venous pressure 32 ± 4 mmHg. A valve-like structure at the junction of the renal and vena cava generated a pressure drop of 12 ± 2 mmHg. RI was 0.27. The renal capsule was durable with a calculated burst pressure of 600 mmHg. Plasma renin and AngII were 2.6 ± 0.5 mIU L(-1) and 9.1 ± 1.5 pg mL(-1) respectively. CONCLUSION: In giraffes, GFR, ERPF and RI appear much lower than expected based on body mass. A strong renal capsule supports a RIHP, which is >10-fold that of other mammals effectively reducing the net filtration pressure and protecting against the high MAP.

Dorzolamide-induced relaxation of porcine retinal arterioles in vitro depends on nitric oxide but not on acidosis in vascular smooth muscle cells.

The carbonic anhydrase inhibitor dorzolamide can induce relaxation of retinal arterioles with a consequent increase in blood flow and oxygenation of the retina. It has been shown that the mechanisms underlying this relaxation are independent of extracellular acidosis and CO2. The purpose of the present study was to investigate the possible involvement of nitric oxide (NO) and intracellular acidosis in dorzolamide-induced relaxation of retinal arterioles. Porcine retinal arterioles were mounted in a wire myograph and dorzolamide induced relaxation was studied after 1) the addition of the NO synthase inhibitor l-NAME (3 × 10(-4) M) or the guanylyl cyclase inhibitor ODQ (3 × 10(-6) M), and 2) after loading the smooth muscle cells with the pH sensitive fluorophore SNARF-1-AM and studying changes in vascular tone and intracellular fluorescence after the induction of hypoxia, addition of lactate (10(-2) M), and extracellular acidification (pH = 7.0) alone and in the presence of dorzolamide (10(-3) M). Dorzolamide significantly relaxed retinal arterioles (p < 0.03), and the effect was significantly higher in the presence of perivascular tissue than in isolated vessels at the highest concentration (p < 0.01). In the presence of perivascular tissue dorzolamide-induced relaxation could be reduced by NO inhibition (p < 0.02). Dorzolamide increased intracellular acidification (p < 0.02) during extracellular acidosis, but there was no relation between relaxation and intracellular acidosis. In conclusion, dorzolamide-induced vasorelaxation depends on NO and the perivascular retinal tissue, but is independent of acidification in the extracellular and the intracellular space of retinal vascular smooth muscle cells. Other factors than NO and acidification are involved in dorzolamide-induced relaxation of retinal arterioles.

Trophic action of sympathetic nerves reduces arterial smooth muscle Ca(2+) sensitivity during early post-natal development in rats.

AIM: A decrease in the Ca(2+) sensitivity of smooth muscle contraction is a hallmark of functional remodelling of blood vessels during development. However, the responsible factors are largely unknown. Here, we tested the hypothesis that the post-natal decline of arterial Ca(2+) sensitivity is the result of trophic effects of sympathetic nerves. METHODS: Contractile responses, intracellular Ca(2+) levels and protein expression profiles were compared in saphenous arteries from young (1- and 2-week-old) and adult rats using wire myography, Ca(2+) fluorimetry and Western blotting respectively. RESULTS: We observed a lower Ca(2+) sensitivity of contractions induced by methoxamine, an agonist of α1 -adrenoceptors, and U46619, an agonist of thromboxane A2 receptors, in arteries from adult as compared to young animals. Post-natal maturation was associated with stronger expression of regulatory proteins mediating Ca(2+) -dependent contraction (myosin light chain kinase (MLCK), myosin targeting subunit (MYPT1) and h-caldesmon) and weaker expression of proteins regulating Ca(2+) -independent contraction (Rho kinase, extracellular-regulated kinases (ERK1/2) and mitogen-activated protein kinases p38 MAPK) in vessels from adult rats. To eliminate the trophic action of sympathetic nerves, we performed lumbar sympathectomy in adult rats. This resulted in higher Ca(2+) sensitivity of agonist-induced contractions in denervated as compared to control arteries. Furthermore, denervated arteries contained less MLCK, MYPT1 and h-caldesmon and more ERK1/2 and p38 MAPK. CONCLUSIONS: Sympathetic denervation reverses developmental changes both in Ca(2+) sensitivity and in the expression of regulatory proteins back to the early post-natal phenotype in the rat saphenous artery. We conclude that trophic effects of sympathetic nerves govern functional remodelling of arteries during early post-natal development.

Impaired myogenic tone in isolated cerebral and coronary resistance arteries from the goto-kakizaki rat model of type 2 diabetes.

AIM: Type 2 diabetes is associated with stroke and cardiac dysfunction. We therefore investigated isolated middle cerebral arteries and coronary septal arteries from the diabetic Goto-Kakizaki (GK) rat model of nonobese type 2 diabetes. METHODS: Myogenic tone and agonist-induced responses were investigated under isobaric conditions with simultaneous recording of [Ca2+]i. Rho-kinase and NO pathways were investigated using specific pharmacological tools. RESULTS: Arteries from GK rats developed less tone at pressures from 20 to 100 mm Hg than arteries from control Wistar (CW) rats while [Ca2+]i was similar. Blocking the Rho-kinase pathway decreased the pressure-induced development of tone and after blockade no difference in myogenic tone between arteries from GK and CW rats was seen. Cerebral arteries had similar tone to a maximal concentration of U46619 (GK: 35.5±2% vs. CW: 31.6±5%), while coronary arteries from GK rats developed less tone than arteries from CW rats (12±3 vs. 26.1±3%). Endothelium-dependent vasodilation to A23187 (cerebral) and to acetylcholine (coronary) was not different between arteries from GK and CW rats. CONCLUSION: Our data suggest that in resistance arteries from the brain and the heart of GK rats the myogenic tone is decreased due to impaired calcium sensitivity likely due to a defective Rho-kinase pathway.

Vasomotion - what is currently thought?

This minireview discusses vasomotion, which is the oscillation in tone of blood vessels leading to flowmotion. We will briefly discuss the prevalence of vasomotion and its potential physiological and pathophysiological relevance. We will also discuss the models that have been suggested to explain how a coordinated oscillatory activity of the smooth muscle tone can occur and emphasize the role of the endothelium, the handling of intracellular Ca(2+) and the role of smooth muscle cell ion conductances. It is concluded that vasomotion is likely to enhance tissue dialysis, although this concept still requires more experimental verification, and that an understanding at the molecular level for the pathways leading to vasomotion is beginning to emerge.

NBCn1 and NHE1 expression and activity in DeltaNErbB2 receptor-expressing MCF-7 breast cancer cells: contributions to pHi regulation and chemotherapy resistance.

Altered pH-regulatory ion transport is characteristic of many cancers; however, the mechanisms and consequences are poorly understood. Here, we investigate how a truncated, constitutively active ErbB2 receptor (DeltaNErbB2) common in breast cancer impacts on the Na(+)/H(+)-exchanger NHE1 and the Na(+),HCO(3)(-)-cotransporter NBCn1 in MCF-7 human breast cancer cells and address the roles of these transporters in chemotherapy resistance. Upon DeltaNErbB2 expression, mRNA and protein levels of NBCn1, yet not of NHE1, increased several-fold, and the localization of both transporters was altered paralleling extensive morphological changes. The rate of pH(i) recovery after acid loading increased by 50% upon DeltaNErbB2 expression. Knockdown and pharmacological inhibition confirmed the involvement of both NHE1 and NBCn1 in acid extrusion. NHE1 inhibition or knockdown sensitized DeltaNErbB2-expressing cells to cisplatin-induced programmed cell death (PCD) in a caspase-, cathepsin-, and reactive oxygen species-dependent manner. NHE1 inhibition augmented cisplatin-induced caspase activity and lysosomal membrane permeability followed by cysteine cathepsin release. In contrast, NBCn1 inhibition attenuated cathepsin release and had no net effect on viability. These findings warrant studies of NHE1 as a potential target in breast cancer and demonstrate that in spite of their similar transport functions, NHE1 and NBCn1 serve different functions in MCF-7 cells.

Jugular venous pooling during lowering of the head affects blood pressure of the anesthetized giraffe.

How blood flow and pressure to the giraffe's brain are regulated when drinking remains debated. We measured simultaneous blood flow, pressure, and cross-sectional area in the carotid artery and jugular vein of five anesthetized and spontaneously breathing giraffes. The giraffes were suspended in the upright position so that we could lower the head. In the upright position, mean arterial pressure (MAP) was 193 +/- 11 mmHg (mean +/- SE), carotid flow was 0.7 +/- 0.2 l/min, and carotid cross-sectional area was 0.85 +/- 0.04 cm(2). Central venous pressure (CVP) was 4 +/- 2 mmHg, jugular flow was 0.7 +/- 0.2 l/min, and jugular cross-sectional area was 0.14 +/- 0.04 cm(2) (n = 4). Carotid arterial and jugular venous pressures at head level were 118 +/- 9 and -7 +/- 4 mmHg, respectively. When the head was lowered, MAP decreased to 131 +/- 13 mmHg, while carotid cross-sectional area and flow remained unchanged. Cardiac output was reduced by 30%, CVP decreased to -1 +/- 2 mmHg (P < 0.01), and jugular flow ceased as the jugular cross-sectional area increased to 3.2 +/- 0.6 cm(2) (P < 0.01), corresponding to accumulation of approximately 1.2 l of blood in the veins. When the head was raised, the jugular veins collapsed and blood was returned to the central circulation, and CVP and cardiac output were restored. The results demonstrate that in the upright-positioned, anesthetized giraffe cerebral blood flow is governed by arterial pressure without support of a siphon mechanism and that when the head is lowered, blood accumulates in the vein, affecting MAP.

Increased contractility to noradrenaline and normal endothelial function in mesenteric small arteries from the Goto-Kakizaki rat model of type 2 diabetes.

UNLABELLED: Type 2 diabetes is associated with many circulatory manifestations, including alteration in endothelial function and hypertension. In this study we investigate the morphology and contractile response as well as the endothelial function of resistance arteries from the spontaneously diabetic Goto-Kakizaki (GK) rat, a model of lean type 2 diabetes expressing glucose intolerance. METHODS: Isolated mesenteric small arteries were investigated under isometric conditions in a wire myograph system using noradrenaline (NA) and the endothelium-dependent vasorelaxant acetylcholine (ACh). Media thickness was measured and media lumen ratio calculated. RESULTS: No apparent morphological difference was noted between the arteries from GK rats and control Wistar (CW) rats. When exposed to the maximal NA concentration used (30 microM), arteries from GK rats developed significantly more tension than arteries from CW rats. In the presence of indomethacin (a specific blocker of the COX synthase) and of L-NAME (an inhibitor of eNOS), the response to NA was still significantly greater in GK rat arteries. Under control conditions, arteries from both groups showed intact relaxation to ACh. After incubation with indomethacin and L-NAME, both groups showed a non-NO nonprostaglandin-dependent relaxation to ACh. This relaxation could be blocked by a combination of apamin and charybdotoxin. CONCLUSION: This study shows that mesenteric small arteries from the diabetic GK rat have increased contractile response to NA, along with a normal endothelial function and unaltered morphology.

Vasomotion has chloride-dependency in rat mesenteric small arteries.

The possibility that Ca(2+)-activated Cl(-) conductances (CaCCs) contribute to oscillations in vascular tone (vasomotion) is tested in isolated mesenteric small arteries from rats where cGMP independent (I (Cl(Ca))) and cGMP-dependent (I (Cl(Ca,cGMP))) chloride conductances are important. The effect of anion substitution and Cl(-) channel blockers on noradrenaline (NA)-stimulated tension in isometrically mounted mesenteric arteries and for chloride conductance of smooth muscle cells isolated from these arteries were assessed electrophysiologically. Cl(-) (o) replacement with aspartate blocked vasomotion while 36mM SCN(-) (o) (substituted for Cl(-)) was sufficient to inhibit vasomotion. Oscillations in tone, membrane potential, and [Ca(2+)](i) disappeared with 36mM SCN(-). DIDS and Zn(2+) blocked I (Cl(Ca,cGMP)) but not I (Cl(Ca)). Vasomotion was not sensitive to DIDS and Zn(2+), and DIDS and Zn(2+) induce vasomotion in arteries without endothelium. The vasomotion in the presence of DIDS and Zn(2+) was sensitive to 36mM SCN(-) (o). The anion substitution data indicate that Cl(-) is crucial for the V (m) and [Ca(2+)](i) oscillations underlying vasomotion. The Cl(-) channel blocker data are consistent with both CaCCs being important.

Rebaudioside A directly stimulates insulin secretion from pancreatic beta cells: a glucose-dependent action via inhibition of ATP-sensitive K-channels.

Recently, we showed that rebaudioside A potently stimulates the insulin secretion from isolated mouse islets in a dose-, glucose- and Ca(2+)-dependent manner. Little is known about the mechanisms underlying the insulinotropic action of rebaudioside A. The aim of this study was to define the signalling system by which, rebaudioside A acts. Isolated mouse islets were used in the cAMP[(125)I] scintillation proximity assay to measure total cAMP level, and in a luminometric method to measure intracellular ATP and ADP concentrations. Conventional and permeabilized whole-cell configuration of the patch-clamp technique was used to verify the effect of rebaudioside A on ATP-sensitive K(+)-channels from dispersed single beta cells from isolated mouse islets. Insulin was measured by radioimmunoassay from insulinoma MIN6 cells. In the presence of 16.7 mM glucose, the addition of the maximally effective concentration of rebaudioside A (10(-9) M) increased the ATP/ADP ratio significantly, while it did not change the intracellular cAMP level. Rebaudioside A (10(-9) M) and stevioside (10(-6) M) reduced the ATP-sensitive potassium channel (K(ATP)) conductance in a glucose-dependent manner. Moreover, rebaudioside A stimulated the insulin secretion from MIN6 cells in a dose- and glucose-dependent manner. In conclusion, the insulinotropic effect of rebaudioside A is mediated via inhibition of ATP-sensitive K(+)-channels and requires the presence of high glucose. The inhibition of ATP-sensitive K(+)-channels is probably induced by changes in the ATP/ADP ratio. The results indicate that rebaudioside A may offer a distinct therapeutic advantage over sulphonylureas because of less risk of causing hypoglycaemia.

Functional abnormalities in isolated arteries from Goto-Kakizaki and streptozotocin-treated diabetic rat models.

Several different rat models have been developed for both type 1 and type 2 diabetes with the aim of displaying specific traits of diabetes. For example, a review on nephropathy associated with type 2 diabetes included 16 different rodent models ; new models are still being developed. The large number of different models developed for different traits makes it difficult to choose the right model for a given study. It is often a problem that the models are not sufficiently characterized, which makes it easy to misinterpret data or even come to the wrong conclusions. In this brief review, we will concentrate on the functional responses obtained in vitro from mesenteric arteries and aortic segments from rat models of diabetes. Since it is beyond the scope of this review to overview all different rodent models of diabetes, we will focus on two commonly used models of diabetes, namely the streptozotocin (STZ)-induced type 1 diabetic rat model and the inbred type 2 diabetic Goto-Kakizaki (GK)-rat model.

Sodium coupled bicarbonate transporters in the kidney, an update.

Recently five genes have been cloned, which code for sodium dependent bicarbonate transport proteins. These genes belong to the SLC4A gene family. This short review summarizes our knowledge of these gene products with respect to their renal distribution and function. The best characterized members are the SLC4A4 and SLC4A7. SLC4A4 codes for an electrogenic Na(+), HCO(3) (-)-cotransporter (NBCe1), which is present in the basolateral membranes of proximal tubules and is responsible for the bicarbonate efflux here, and thus about 80% of the renal bicarbonate reabsorption. SLC4A7 codes for an electroneutral NBC (called NBC3 and NBCn1), which is present basolaterally in the thick ascending limb and the distal part of the collecting ducts and in intercalated cells (either apically or basolaterally) in the connecting and collecting tubules. In the thick ascending limb NBCn1 may be important for NH(4) (+) reabsorption. SLCA5 codes for an electrogenic NBC (called NBC4 and NBCe2), which based on RT-PCR is located to the kidney but the exact localization awaits a good antibody. This is also the case for the SLC4A8 and SLC4A10 gene products, which are sodium dependent Cl(-), HCO(3) (-) exchangers. The recent development in this field substantially increases our understanding of the complex renal regulation of acid base status.

Immunolocalization of electroneutral Na(+)-HCO cotransporters in human and rat salivary glands.

Patterns of salivary HCO secretion vary widely among species and among individual glands. In particular, virtually nothing is known about the molecular identity of the HCO transporters involved in human salivary secretion. We have therefore examined the distribution of several known members of the Na(+)-HCO cotransporter (NBC) family in the parotid and submandibular glands. By use of a combination of RT-PCR and immunoblotting analyses, the electroneutral cotransporters NBC3 and NBCn1 mRNA and protein expression were detected in both human and rat tissues. Immunohistochemistry demonstrated that NBC3 was present at the apical membranes of acinar and duct cells in both human and rat parotid and submandibular glands. NBCn1 was strongly expressed at the basolateral membrane of striated duct cells but not in the acinar cells in the human salivary glands, whereas little or no NBCn1 labeling was observed in the rat salivary glands. The presence of NBCn1 at the basolateral membrane of human striated duct cells suggests that it may contribute to ductal HCO secretion. In contrast, the expression of NBC3 at the apical membranes of acinar and duct cells in both human and rat salivary glands indicates a possible role of this isoform in HCO salvage under resting conditions.

Endothelial dysfunction in resistance arteries is related to high blood pressure and circulating low density lipoproteins in previously treated hypertension.

BACKGROUND: Peripheral endothelial dysfunction has been demonstrated in hypertension. However, its relationship to blood pressure (BP) load, vascular structure, and metabolic disturbances in patients with long-standing, previously treated hypertension is unclear. METHODS: A total of 41 patients with stage I to III essential hypertension and electrocardiographic left ventricular hypertrophy were studied. After 2 to 3 weeks of placebo treatment we measured nitroprusside-induced relaxation (NIR), acetylcholine-induced relaxation (AIR), and media:lumen ratio in isolated, subcutaneous resistance arteries by myography, as well as 24-h ambulatory BP, and serum lipids. RESULTS: Maximal AIR correlated negatively with median 24-h diastolic BP (r=-0.42, P=.01), and sensitivity to AIR correlated negatively with serum low density lipoprotein (LDL) (r =-0.36, P < .05). In multiple regression analyses, sensitivity to AIR correlated negatively with serum LDL (beta=-0.33) independently of maximal NIR (beta=0.41) (adjusted R2 =0.26, P < .01). Maximal acetylcholine-induced relaxation correlated negatively with median 24-h diastolic BP (beta=-0.38) independently of maximal NIR (beta=0.45) (adjusted R2= 0.32, P < .001). Acetylcholine-induced relaxation was not significantly related to diabetes or to media:lumen ratio (r = -0.26, NS). CONCLUSIONS: High diastolic BP and high serum LDL were associated with impaired maximal AIR and reduced sensitivity to AIR, respectively, independently of smooth muscle cell responsiveness to nitroprusside. This indicated decreasing endothelial function in small resistance arteries with increasing BP and increasing LDL in hypertension. Endothelial function was not significantly related to vascular structure of the resistance arteries or to diabetes in these patients with long-standing hypertension.

Effects of oophorectomy on functional properties of resistance arteries isolated from the cancellous bone of the rabbit femur.

Information is sparse concerning the effect of oophorectomy (OOX) on bone vascularization and blood flow of possible significance for altered remodeling. Whether OOX affects functional characteristics of isolated bone resistance arteries was investigated. Ring preparations (diameter approximately 250 microm) of small femoral bone arteries from oophorectomized and sham-operated rabbits were mounted on a myograph six weeks postoperatively. Cumulative concentration response curves were obtained for various agonists at a normalized lumen diameter. Oophorectomy did not significantly influence lumen diameter, maximal response to high potassium, or maximal response to high potassium and 10(-5) M noradrenaline. However, OOX significantly increased the maximal response to noradrenaline (OOX 2.14 +/- 0.36 N/m, Sham 1.25 +/- 0.14 N/m) and endothelin-1 (OOX 1.76 +/- 0.32, Sham 0.95 +/- 0.15) in metaphyseal arteries. Moreover, the corresponding maximal active pressure for the agonists was significantly increased. OOX did not influence endothelial function assessed by the effects of acetylcholine or substance P. The functional responses of diaphyseal arteries were unaffected by OOX. The study demonstrates regional differences in the effects of OOX on small arteries of importance for control of vascular resistance in bone which suggests a relation between altered vascular function after ovarian hormonal withdrawal and the changes in bone turnover associated with osteoporosis.

Differential effects of angiotensin AT1 and AT2 receptors on the expression, translation and function of the Na+-H+ exchanger and Na+-HCO3- symporter in the rat heart after myocardial infarction.

OBJECTIVES: This study investigated the role of angiotensin receptor subtype 1 (AT1) and angiotensin receptor subtype 2 (AT2) in the regulation of Na+-H+ exchanger (NHE) and Na+-HCO3 symporter (NBC) in the infarcted myocardium. BACKGROUND: The cardiac renin-angiotensin system is activated after myocardial infarction (MI), and both angiotensin AT1 and AT2 receptors are upregulated in the myocardium. METHODS: Na+-H+ exchanger isoform-1 and NBC-1 gene expression were determined by reverse transcription polymerase chain reaction and Northern blot analysis; protein levels by Western blot analysis; and activity by measurement of H+ transport in left ventricular (LV) free wall, interventricular septum (IS) and right ventricle (RV) after induction of MI. Rats were treated with placebo, the angiotensin-converting enzyme inhibitor ramipril (1 mg/kg/day), the AT1 receptor antagonist valsartan (10 mg/kg/day) or the AT2 receptor antagonist PD 123319 (30 mg/kg/day). Treatment was started seven days before surgery. RESULTS: Na+-H+ exchanger isoform-1 and NBC-1 messenger RNA (mRNA) expression and protein levels were increased twofold in the LV free wall after MI, whereas no changes were observed in the IS and RV. Na+-dependent H+ flux was increased in the LV free wall. Ramipril inhibited mRNA and protein upregulation of both transporters. Valsartan inhibited the upregulation of NHE-1 mRNA and protein but had no effect on NBC-1 mRNA expression and translation. In contrast, PD 123319 abolished the upregulation of NBC-1 mRNA and protein but had no effect on NHE-1 upregulation. Ramipril and valsartan prevented post-MI increase in NHE-1 activity, whereas ramipril and PD 123319 decreased NBC-1 activity. CONCLUSIONS: Angiotensin II via its AT1 and AT2 receptors differentially controls transcriptional and translational regulation as well as the activity of NHE-1 and NBC-1 in the ischemic myocardium and contributes to the control of pH regulation in cardiac tissue.

Adrenergic responses in human small arteries isolated from the femoral neck.

Many pathological bone conditions are accompanied by changes in bone perfusion. However, no method has yet allowed investigation of vascular reactivity in human bone tissue. In the present study, arterial segments (diameter approximately 0.25 mm) were isolated from human bone biopsies and mounted as ring preparations in vitro. The viability of the arteries and the effects of adrenoceptor stimulations were investigated. Combined alpha- and beta-adrenoceptor stimulation (noradrenaline 10(-8)-10(-5) M) and specific alpha1-adrenoceptor stimulation (phenylephrine, 10(-8)-10(-4.5) M) induced concentration-dependent contractions in all arteries. Selective stimulation of alpha2-receptors (B-HT 933, 10(-8)-10(-3.5) M) only induced contraction in three of eight arteries. Stimulation of beta-receptors with isoprenaline (10(-6) M) resulted in vasorelaxation in 3 of 10 arteries. In all arteries, acetylcholine (10(-10)-10(-5) M) induced vasorelaxation, demonstrating preserved function of the endothelium. The results suggest that primarily alpha1-receptors are responsible for adrenoceptor induced vasoconstriction in human bone while functional alpha2- and beta-receptors may not be consistently expressed. The model is the first to allow investigations on vascular reactivity in human bone tissue and may become valuable for assessment of both normal and pathological bone physiology.

Hypothesis for the initiation of vasomotion.

Vasomotion is the regular variation in tone of arteries. In our study, we suggest a model for the initiation of vasomotion. We suggest that intermittent release of Ca(2+) from the sarcoplasmic reticulum (SR, cytosolic oscillator), which is initially unsynchronized between the vascular smooth muscle cells, becomes synchronized to initiate vasomotion. The synchronization is achieved by an ion current over the cell membrane, which is activated by the oscillating Ca(2+) release. This current results in an oscillating membrane potential, which synchronizes the SR in the vessel wall and starts vasomotion. Therefore, the pacemaker of the vascular wall can be envisaged as a diffuse array of individual cytosolic oscillators that become entrained by a reciprocal interaction with the cell membrane. The model is supported by experimental data. Confocal [Ca(2+)](i) imaging and isometric force development in isolated rat resistance arteries showed that low norepinephrine concentrations induced SR-dependent unsynchronized waves of Ca(2+) in the vascular smooth muscle. In the presence of the endothelium, the waves converted to global synchronized oscillations of [Ca(2+)](i) after some time, and vasomotion appeared. Synchronization was also seen in the absence of endothelium if 8-bromo-cGMP was added to the bath. Using the patch-clamp technique and microelectrodes, we showed that Ca(2+) release can activate an inward current in isolated smooth muscle cells from the arteries and cause depolarization. These electrophysiological effects of Ca(2+) release were cGMP dependent, which is consistent with the possibility that they are important for the cGMP-dependent synchronization. Further support for the model is the observation that a short-lasting current pulse can initiate vasomotion in an unsynchronized artery as expected from the model.