Effects of substrate and hypoxia on smooth muscle metabolism and contraction

Chronic high-fat diet decreased detrusor mitochondrial respiration and increased nerve-mediated contractions

AIMS

To assess the impact of chronic high-fat diet (HFD) on behavioral voiding patterns, detrusor contractility, and smooth muscle mitochondrial function in male mice.

MATERIALS AND METHODS

Male C57BL/6J mice (6 weeks) were fed a control or HFD for 20 weeks. Bladder function was assessed by void spot assays. Bladders were collected and detrusor contractility to carbachol (10^-9 -10^-5  M), and electrical field stimulation (EFS, 0.5-32 Hz) in the presence and absence of atropine was measured. Homogenized detrusor samples were placed in oxygraphs to assess the rate of oxygen consumption of the mitochondria within the detrusor in the presence of different substrates. Mitochondrial hydrogen peroxide (H₂ O₂ ) emission was measured fluorometrically. Detrusor citrate synthase activity was measured via enzyme activity kit and Western blots assessed the electron transport chain (ETC) protein content.

RESULTS

HFD significantly increased body weight, adiposity, and blood glucose levels. HFD mice demonstrated increased voiding frequency and increased EFS-induced detrusor contractility. There were no changes in detrusor relaxation or cholinergic-medicated contraction. Mitochondrial respiration was decreased with HFD and H₂ O ₂ emission was increased. The relative amount of mitochondria in the detrusor was similar between groups. However, ETC complexes V and III were increased following HFD.

CONCLUSIONS

Chronic HFD increased adiposity, lead to more frequent voiding, and enhanced EFS-mediated detrusor contractions. Mitochondrial respiration was decreased and H₂ O ₂ emission increased following HFD. Further research is required to determine if alterations in mitochondrial function could play a role in the development of HFD-induced bladder dysfunction.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Effects of metabolic stress and ischaemia on the bladder, and the relationship with bladder overactivity

The bladder wall becomes to ischaemic when intravesical pressure rises above capillary pressure. This will occur routinely in bladders with outflow obstruction. Experiments in vitro show that the detrusor normally uses anaerobic as well as aerobic metabolism. Anoxic conditions result in an initial reduction in contractility, but significant contractile ability persists. Substrate removal causes a slow progressive fall in contractility as glycogen stores deplete. Removal of substrate and oxygen causes rapid loss of contractile ability and permanently damages intrinsic nerves, although the detrusor recovers well. In vivo ischaemia in animal models results in bladder overactivity and the expression of apoptotic markers in intrinsic neurons in the bladder wall. In humans, bladders from patients with bladder instability show patchy denervation, suggesting that periodic ischaemia and neuronal death may predispose to overactivity.

Calcium, mitochondria and oxygen sensing in the pulmonary circulation

A key event in hypoxic pulmonary vasoconstriction (HPV) is the elevation in smooth muscle intracellular Ca2+ concentration. However, there is controversy concerning the source of this Ca2+, the signal transduction pathways involved, and the identity of the oxygen sensor. Although there is wide support for the hypothesis that hypoxia elicits depolarisation via inhibition of K+ channels, and thus promotes Ca2+ entry through L-type channels, a significant number of studies are inconsistent with this mechanism being either the sole or even major means by which Ca2+ is elevated during HPV. There is strong evidence that intracellular Ca2+ stores play a critical role, and voltage-independent Ca2+ entry mechanisms including capacitative Ca2+ entry (CCE) have also been implicated. There is renewed interest in the role of mitochondria in HPV, both in terms of modulators of Ca2+ homeostasis per se and as oxygen sensors. There is however considerable uncertainty concerning the mechanisms involved in the latter, with proposals for changes in redox couples and both an increase and decrease in mitochondrial production of reactive oxygen species (ROS). In this article we review the evidence for and against involvement of such mechanisms in HPV, and propose a model for the regulation of intracellular [Ca2+] in pulmonary artery during hypoxia in which the mitochondria play a central role.

Insulin increases glycolysis without further vasodilation in porcine coronary arteries exposed to hypoxia

In acute ischaemia, glucose-insulin-potassium administration reduces mortality and beta-adrenoceptor antagonists have favourable effects on the outcome of ischaemic heart disease. The present study was designed to investigate whether insulin (1.4x10(-7) M) and the beta-adrenoceptor antagonist, propranolol (10(-5) M), increase hypoxic vasodilation in correspondence with changes in glycolysis. Porcine coronary arteries, precontracted with 10(-5) M prostaglandin F(2alpha), were mounted in a pressure myograph and a microdialysis catheter was inserted in the tunica media. Hypoxic vasodilation, interstitial lactate/pyruvate ratio and interstitial glucose were measured at low (2 mM) and high (20 mM) glucose concentrations. Hypoxia (60 min) caused vasodilation and doubled the lactate/pyruvate ratio. Treatment with insulin quadrupled the lactate/pyruvate ratio during hypoxia, but did not change hypoxic vasodilation. Propranolol blocked isoprenaline-evoked vasodilation, but hypoxic increases in lactate/pyruvate ratio and vasodilation did not change. The combination of insulin and propranolol did not cause further changes compared with each drug added alone, although the combination increased vasoconstriction during reoxygenation. Interstitial glucose fell during hypoxia at an organ bath glucose concentration of 2 mM, and rose at a glucose concentration of 20 mM. Addition of insulin and propranolol alone or in combination had no effect on interstitial glucose concentration. Accordingly, arteries were found to contain only minute amounts of the glucose transporter isoform GLUT4. Our findings suggest that insulin increases arterial glycolysis, but treatment with insulin, propranolol, or both, is not associated with enhanced coronary vasodilation during hypoxia.

Mitochondrial Oxidative Substrate Selection in Porcine Bladder Smooth Muscle

PURPOSE

Alterations in bladder smooth muscle (BSM) metabolism due to alterations in plasma lipid levels may be important with the increasingly high fat diets eaten by most Americans. To determine the susceptibility of BSM to lipotoxicity we examined the normal pattern of mitochondrial substrate selection in BSM and the ability of BSM to respond to changes in metabolic substrate provision.

MATERIALS AND METHODS

BSM strips were incubated in 5 mM 1-13C-glucose and 0 to 5 mM 1,2-13C-acetate. The pattern of substrate use measured by 13C-nuclear magnetic resonance using BSM extracts. BSM was also cultured for 4 days to elicit changes in cell phenotype.

RESULTS

At physiological levels of glucose and acetate about 50% of the substrate used by mitochondria was glucose. When acetate concentration was changed from physiological levels (0.1 mM) to pathophysiological levels (0.5 mM), BSM was able to increase the use of acetate, while sparing the use of glucose and intracellular substrates, likely lipids. Above 0.5 mM acetate BSM was unable to further use acetate. With increasing acetate use anaplerosis increased, consistent with a depletion of tricarboxylic acid cycle intermediates. After 4 days of organ culture BSM mitochondria used significantly more unlabeled intracellular substrates and less 13C labeled glucose than control bladder, consistent with metabolic adaptation to increase lipid use, such as what occurs with hyperlipidemia.

CONCLUSIONS

We conclude that BSM has modest plasticity of the pattern of mitochondrial substrate selection and excess lipid provision may be able to induce lipotoxicity in BSM, resulting in impaired detrusor function.

A description of Ca2+ channels in human detrusor smooth muscle

OBJECTIVE

To characterize the Ca2+ channels in human detrusor smooth muscle and to investigate their contribution to spontaneous electrical activity.

MATERIALS AND METHODS

Isolated human detrusor smooth muscle myocytes were used to measure ionic currents under voltage-clamp or membrane potential under current-clamp. Membrane potential oscillations were analysed in terms of oscillation frequency and amplitude using fast Fourier transforms.

RESULTS

Under voltage-clamp an inward current dependent on extracellular Ca2+ was recorded using Cs+-filled patch electrodes. The current could be separated into two components on the basis of their sensitivity to Ni2+, verapamil or nicardipine, and their dependence on holding and clamp potential. A Ni2+-sensitive component activated over a relatively negative range of potentials (-60 to -20 mV) comprised about a third of the total current and was designated a T-type Ca2+ current. A verapamil/nicardipine-sensitive component, activated at more positive potentials, was designated an l-type Ca2+ current. Using K+-based filling solutions spontaneous transient outward currents were recorded that had the characteristics of current flow through BK channels. Membrane potential oscillations, under current-clamp increased in frequency but not amplitude as the mean membrane potential was made less negative. The voltage-dependence of oscillation frequency was similar to that of the l-type, but not T-type, Ca2+ current activation curve. Furthermore oscillation frequency was slowed by verapamil but not Ni2+.

CONCLUSION

The study showed, for the first time, the presence of both T- and L-type Ca2+ channels in human detrusor smooth muscle; we propose a role for these channels in spontaneous activity. The results suggest that the L-type Ca2+ current can control membrane potential oscillation frequency. The significance of this finding for spontaneous contractions is discussed.

Energy cost of contraction in rat urinary bladder smooth muscle during anoxia

1. The aim of the present study was to investigate the effects of hypoxia on energy metabolism and contraction of rat urinary bladder smooth muscle, thereby gaining insight into the capacity of this smooth muscle to maintain contractile function when rendered hypoxic. 2. Isometric force, oxygen consumption, lactate production, heat production and unloaded shortening velocity were measured in isolated muscle strips under both aerobic and anaerobic conditions. Muscle strips were bathed in physiological saline solution with the anaerobic condition being created by replacing the oxygen bubbling the solution with nitrogen. 3. During contraction under anaerobic conditions, the rate of lactate production was increased 2.5-fold above that observed under aerobic conditions. This, however, only provided for a rate of ATP production of approximately 30% of that measured under aerobic conditions. Despite this, force maintenance was only slightly depressed, indicating that the metabolic cost of contraction was reduced in hypoxia. In support of this, the rate of heat production during contractions in anoxia was only approximately half of that under aerobic conditions, whereas, again, force was only slightly lower. Unloaded shortening velocity was significantly lower in anoxia, suggesting a slower cross-bridge turnover rate. 4. The results indicate that the economy of force maintenance is increased in bladder smooth muscle under hypoxic conditions and that this is due, at least in part, to a reduced rate of cross-bridge cycling. This may help to preserve bladder contractile function during periods of ischaemia that may be associated with bladder filling and emptying.

Role of the T-type Ca2+ current on the contractile performance of guinea pig detrusor smooth muscle

AIMS

The importance of the T-type Ca(2+) current in determining detrusor contractile function was investigated by using guinea pig muscle in vitro.

METHODS

NiCl(2) (200 microM) was used to block selectively the T-type Ca(2+) current, and 20 microM verapamil was used to block the L-type Ca(2+) current in this tissue. The selectivity of these agents at such concentrations has been previously demonstrated.

RESULTS

In normal extracellular solution (4 mM KCl) 200 microM NiCl(2) and 20 microM verapamil reduced electrically stimulated contractions by 17 +/- 6% and 65 +/- 10%, respectively. At high concentrations of the two agents, the contraction was completely abolished by NiCl(2) but by only 74 +/- 18% in the case of verapamil; this finding suggests that NiCl(2) has additional negative inotropic actions at higher concentrations. Carbachol and KCl contractures were attenuated to a similar extent to that of electrically stimulated contractions by NiCl(2) and verapamil, which suggests that they act on the muscle rather than the motor nerve. The dependence of the membrane potential on the relative ability of NiCl(2) and verapamil to attenuate the contraction was tested by varying the extracellular [KCl], [KCl](o). Varying [KCl](o) between 2 and 10 mM depolarised detrusor myocytes from (-65.1 +/- 4.7 mV to -42.7 +/- 4.0 mV (a slope of 32 mV per 10-fold change of [KCl](o)). In low [KCl](o),blockade by NiCl(2) was more effective and that of verapamil less effective; at high [KCl](o), the reverse potency was recorded.

CONCLUSIONS

The data are consistent with the hypothesis that Ca(2+) influx through both T-type and L-type Ca(2+) channels determines the contractile status of detrusor smooth muscle and that T-type channel activity is more important at membrane potentials near the resting level. A significant role for T-type channel activity in the resting state was evident in that spontaneous contractions were attenuated to a greater extent than evoked contractions.

Hypoxia, energy state and pulmonary vasomotor tone

Vasomotor responses to hypoxia constitute a fundamental adaptation to a commonly encountered stress. It has long been suspected that changes in cellular energetics may modulate both hypoxic systemic artery vasodilatation (HSV) and hypoxic pulmonary artery vasoconstriction (HPV). Although limitation of energy has been shown to underlie hypoxic relaxation in some smooth muscles, the response to hypoxia in vascular smooth muscle does not appear to be a simple function of energy stores, but instead may involve perturbations of ATP or energy delivery to mechanisms controlling muscle force, and/or changes associated with anaerobic metabolism. Recent work in pulmonary vascular smooth muscle has demonstrated that energy stores are maintained during hypoxic pulmonary vasoconstriction, and that this is dependent on glucose availability and up-regulation of glycolysis. There is increasing evidence that glycolysis is preferentially coupled to a variety of membrane associated ATP dependent processes, including the Na(+) pump, Ca(2+)-ATPase, and possibly some protein kinases. These and other mechanisms may influence excitation-contraction coupling in both systemic and pulmonary arteries by effects on intracellular Ca(2+) and/or Ca(2+) sensitivity. Hypoxia has also been postulated to have major effects on other cytosolic second messenger systems including phosphatidylinositol pathways, cell redox state and mitochondrial reactive oxygen species production. This review examines the relationship between energy state, anaerobic respiration and hypoxic vasomotor tone, with a particular emphasis on hypoxic pulmonary vasoconstriction.

Divergent roles of glycolysis and the mitochondrial electron transport chain in hypoxic pulmonary vasoconstriction of the rat: identity of the hypoxic sensor

1. The mechanisms responsible for sensing hypoxia and initiating hypoxic pulmonary vasoconstriction (HPV) are unclear. We therefore examined the roles of the mitochondrial electron transport chain (ETC) and glycolysis in HPV of rat small intrapulmonary arteries (IPAs). 2. HPV demonstrated a transient constriction (phase 1) superimposed on a sustained constriction (phase 2). Inhibition of complex I of the ETC with rotenone (100 nM) or complex III with myxothiazol (100 nM) did not cause vasoconstriction in normoxia, but abolished both phases of HPV. Rotenone inhibited the hypoxia-induced rise in intracellular Ca(2+) ([Ca(2+)](i)). Succinate (5 mM), a substrate for complex II, reversed the effects of rotenone but not myxothiazol on HPV, but did not affect the rise in NAD(P)H fluorescence induced by hypoxia or rotenone. Inhibition of cytochrome oxidase with cyanide (100 microM) potentiated phase 2 constriction. 3. Phase 2 of HPV, but not phase 1, was highly correlated with glucose concentration, being potentiated by 15 mM but abolished in its absence, or following inhibition of glycolysis by iodoacetate or 2-deoxyglucose. Glucose concentration did not affect the rise in [Ca(2+)](i) during HPV. 4. Depolarisation-induced constriction was unaffected by hypoxia except in the absence of glucose, when it was depressed by approximately 50 %. Depolarisation-induced constriction was depressed by rotenone during hypoxia by 23 +/- 4 %; cyanide was without effect. 5. Hypoxia increased 2-deoxy-[(3)H]glucose uptake in endothelium-denuded IPAs by 235 +/- 32 %, and in mesenteric arteries by 218 +/- 38 %. 6. We conclude that complex III of the mitochondrial ETC acts as the hypoxic sensor in HPV, and initiates the rise in smooth muscle [Ca(2+)](i) by a mechanism unrelated to changes in cytosolic redox state per se, but more probably by increased production of superoxide. Additionally, glucose and glycolysis are essential for development of the sustained phase 2 of HPV, and support an endothelium-dependent Ca(2+)-sensitisation pathway rather than the rise in [Ca(2+)](i).

Renal vascular and biochemical responses to systemic renin inhibition in dogs at low renal perfusion pressure

Renin is produced by the kidney and secreted into the systemic circulation. However, its biochemical and physiological role of regulating renal blood flow with changing renal perfusion pressure (RPP) is not fully understood. In this study, the function of the intrarenal renin for production of angiotensin (Ang) I and maintenance of vascular tone was evaluated in dogs under normal conditions and when the kidney was perfused at low RPP. The dog left kidney was perfused first at normal (100 mm Hg) and then at low (30 mm Hg) RPP in the presence or absence of the renin inhibitor ciprokiren (3 mg/kg, i.v.). Both hemodynamic and biochemical parameters were measured. Lowering RPP markedly reduced left renal blood flow and elevated left renal vascular resistance. These effects were prevented by ciprokiren, which blocked the intrarenal production of Ang I. Lowering RPP increased the renal venous/ arterial ratio from 1.4+/-0.1 to 3.6+/-0.3 for plasma renin activity and from 2.4+/-0.2 to 9.8+/-1.1 for Ang I, but did not change the venous/arterial ratio for Ang II. The net renal venous conversion rate of Ang I to Ang II decreased from 0.22 to 0.09 after RPP was lowered, whereas the conversion rate in arterial blood was 1.35 and did not decrease significantly. Our results demonstrated the importance of intrarenal renin-angiotensin system for Ang I production and for the maintenance of the vascular tone, especially at low RPP. Our study also shows the limited capacity for Ang I conversion in the renal vasculature in vivo.

The inhibitory effect of fluoride on carbachol-induced bovine bronchial contraction

The effect of sodium fluoride (NaF) on the responsiveness of airway smooth muscle was investigated in bovine bronchial segments. NaF (0.5-10 mM) induced a delayed concentration-dependent active pressure (AP) and reduced the lactate concentration in the solution. Pyruvate (10 mM) increased the NaF-induced contraction. There was a 50 +/- 7% decrease in carbachol (10 microM)-induced AP when bronchi were pretreated with NaF (5 mM) and a 37 +/- 9% decrease when NaF (5 mM) was added during the maintained carbachol-induced contraction. These inhibitory effects were enhanced by KCN and hypoxia. When bronchi were pre-incubated with 10 microM verapamil, a calcium channel inhibitor, the contractile effect of 5 mM NaF was reduced to 8 +/- 3% of the control. PKC activity in bronchial smooth muscle was significantly increased by NaF (5 mM). Staurosporine (30 nM) abolished the contractile effect of NaF. These results suggest that: (1) NaF either contracts or relaxes bronchial smooth muscle depending on the experimental conditions; (2) the relaxing effect is related to the inhibitory action of NaF on glycolysis; (3) the contractile effect of NaF is possibly mediated by modulation of a calcium channel via a PKC-dependent pathway; (4) carbachol-induced contraction is glycolysis pathway dependent in the absence of NaF but switches to oxidative dependent in its presence.

Tissue renin-angiotensin system: a site of drug action?

In this review, we present background material that provides partial support for a tissue renin-angiotensin system (RAS). Evidence for the existence of this system relied in part on the use of drugs, which has entailed using low doses or concentrations of angiotensin-converting enzyme inhibitors, renin inhibitors, and angiotensin antagonists to block the RAS in vascular beds and in isolated arteries or organs. Other evidence for a tissue RAS has depended upon measurements of the components of the system, i.e. enzymes, substrates, and mRNAs for these proteins. All of these components were first believed to be present in the heart and blood vessels; however, it is now known that renin in the circulating blood derived from the kidney is used for the local synthesis of angiotensins. The main emphasis of the review is on the renal RAS because it is believed that the local RAS is most prominent in this organ. The renal RAS is probably involved in the long-rather than short-term regulation of renal vascular resistance and maintenance of normal blood pressure through the regulation of sodium reabsorption.

Effects of glucose deprivation on the contractile response of the rabbit bladder to repetitive stimulation

The urinary bladder requires an adequate energy supply to maintain contractile function. The primary metabolic fuel is glucose. Through glycolysis and oxidative phosphorylation, high energy phosphates are generated, which in turn supply the metabolic energy for the contractile activities of the urinary bladder. The aim of this study was to determine the effects of glucose deprivation and recovery from glucose deprivation on the phasic and tonic components of the contractile responses of rabbit bladder strips to field stimulation, bethanechol, and KCl. The results can be summarized as follow: In response to glucose deprivation, (1) the tonic responses to field stimulation, bethanechol, and KCl all decreased at a significantly greater rate than the phasic responses; (2) the phasic and tonic responses to field stimulation were both reduced to less than 10% of control within 70 minutes of initiating glucose deprivation; (3) the tonic responses to bethanechol and KCI were reduced to approximately 10% of control within 180 minutes whereas the phasic responses remained stable at 40 and 30%, respectively; and (4) glucose replacement stimulated a rapid and nearly complete recovery of the phasic and tonic components of the responses to field stimulation, bethanechol, and KCI. These results indicate that the tonic responses to all forms of stimulation are more sensitive to glucose deprivation than the phasic responses.

Plasma angiotensin in binephrectomised mice

Plasma renin-angiotensin parameters were measured before and 24h after binephrectomy (BNx) in male Swiss (Ren-1, Ren-2) and BALB/c (Ren-1) female mice (representing the extremes of differences in tissue renin expression), together with in vivo inhibition of residual renin. Plasma Ang II increased from 18.9 +/- 7.3 to 48.1 +/- 16.9 pg/ml after BNx in conscious Swiss mice (+/- sd, p < 0.001, n = 11&12), renin activity (PRA) increased 2.76 times, angiotensinogen (aogen) increased 4.57 times and renin concentration (PRC) fell by 65%. In BALB/c, Ang II+Ang III decreased slightly (56.6 +/- 11 to 37.7 +/- 14.7, p < 0.05, n = 5&6), PRA was unchanged, aogen increased 12 times and PRC fell by 93%. Plasma ACE decreased by 26% and 28% respectively. Aogen did not increase further when post BNx plasma renin was inhibited with antirenin in vivo during 20h. Thus plasma angiotensin is maintained or considerably increased following BNx in mice and the change is consistent with first-order kinetics with respect to renin and aogen in the circulation. Whether the strain carries one or two renin genes, high renal and extrarenal renin production combined with a low plasma aogen phenotype yields resting angiotensin levels similar to other mammals. A kinetic regulation of aogen levels is proposed in mice wherein Ang II production is limited by low substrate concentration thereby ensuring normotension in the face of abundant extrarenal renin secretion.

Angiotensin-converting enzyme gene polymorphism has no influence on the circulating renin-angiotensin-aldosterone system or blood pressure in normotensive subjects

BACKGROUND

Angiotensin-converting enzyme (ACE) is involved in the metabolism of two major vasoactive peptides, converting angiotensin (Ang) I into Ang II and inactivating bradykinin. An insertion/deletion (I/D) polymorphism is present in the 16th intron of the ACE gene and is strongly associated with plasma and cellular ACE levels. Contrasting with the lack of relation between ACE gene polymorphism and blood pressure level, a large case-control study has shown that the deletion marker allele of the ACE gene was associated with an increased risk of myocardial infarction. The pathophysiological link between ACE gene polymorphism and cardiovascular events remains hypothetical. One hypothesis is that this polymorphism influences Ang II and bradykinin concentrations in the peripheral and/or local circulations through its effects on ACE levels in plasma and endothelial cells. The aim of this study was to investigate the effect of the ACE gene I/D polymorphism on blood pressure, plasma active renin, and aldosterone regulation in normal subjects.

METHODS AND RESULTS

Twenty-four normotensive male volunteers homozygous for the ACE I/D polymorphism (12 DD and 12 II) received a renin inhibitor infusion (remikiren 0.1 mg.kg-1.h-1 for 130 minutes) to suppress endogenous Ang I and Ang II production. Forty minutes after initiating the remikiren infusion, an exogenous Ang I infusion was begun and increased gradually every 15 minutes from 1 to 10 ng.kg-1.min-1. Median (range) plasma ACE levels (mU/mL) were 39 (32 to 57) and 24 (12 to 30) in the DD and II groups, respectively. Remikiren suppressed plasma Ang I and Ang II, increased plasma active renin (from 23 +/- 12 to 154 +/- 161 pg/mL), decreased plasma aldosterone (from 106 +/- 42 to 82 +/- 33 pg/mL), and slightly decreased diastolic blood pressure (from -2.4 +/- 2.7 mm Hg). The blood pressure and hormonal responses to Ang I infusion after renin inhibition and the slope of the rise in plasma Ang II with increasing Ang I dose were identical in both groups, as was the plasma Ang I/Ang II ratio before (DD, 2.09 +/- 1.04; II, 2.59 +/- 0.76) and after (DD, 0.15 +/- 0.13; II, 0.09 +/- 0.03) combined renin inhibitor and Ang I infusion.

CONCLUSIONS

Despite its association with a major difference in plasma ACE levels, the ACE I/D polymorphism did not influence the Ang II and plasma aldosterone production, plasma active renin decrease, or diastolic blood pressure increase induced by exogenous Ang I infusion, suggesting that ACE has no limiting influence on systemic Ang II generation and effects under these experimental conditions.

Bronchial smooth muscle energetics: effect of iodoacetate and hypoxia

The active pressure (AP) and the oxygen consumption (VO2) of segments of bovine bronchi were measured during a 10 microM carbachol stimulation. VO2 did not increase during the carbachol-induced contraction whereas there was a twofold increase in the lactate production. Addition of the glycolytic blocker, iodoacetate (83 microM), decreased the AP to 68.9 +/- 6.4% of control value (n = 10, P < 0.05) whereas VO2 remained constant. The lactate concentration in the physiological solution decreased significantly (P < 0.05). When the solution was supplemented with pyruvate (10 mM), the effect of iodoacetate was antagonized. Under hypoxic condition, i.e. when the solution was bubbled with 5% CO2 in N2, VO2 decreased sharply to 7.7 +/- 3.1% of control (n = 8, P < 0.05) whereas AP did not change. The combined effect of iodoacetate and hypoxia led to a fall in both AP (12.4 +/- 3.0% of control, n = 7, P < 0.05) and VO2 (21.2 +/- 5.1%, P < 0.05). These results suggest that the energy required by bronchial smooth muscle to generate contraction could be supplied by either the aerobic or the anaerobic pathway.

Contractile and metabolic properties of longitudinal smooth muscle from rat urinary bladder and the effects of aging

Longitudinal smooth muscle strips taken from the urinary bladders of Sprague-Dawley rats, aged approximately 6 months and 24 months, were examined under a variety of conditions. Force development in response to electrical field stimulation and to cumulative addition of Ca2+ in the continual presence of 64 mM. KCl was the same in both adult and aged preparations. In response to cumulative additions of carbachol, however, it was observed that there was a shift to the right of the dose-response curve and a decrease in maximal force in the aged muscle strips. The maximal velocity of shortening was significantly lower in muscles from aged animals than in those from young adult animals. The metabolic tension cost during isometric contraction was, however, the same in both groups suggesting that the decline in Vus is largely due to factors not influencing energetic cost. The aged muscles also exhibited a lower basal metabolic rate and a reduced contribution of aerobic glycolysis to total metabolic energy production during both quiescence and stimulation under normoxic conditions than did muscles from young adult animals. They were, however, able to increase their rate of lactate production to the same levels as young adult muscles when stimulated under anoxic conditions.

Activation of mouse renin promoter by cAMP and c-Jun in a kidney-derived cell line

We demonstrated that the mouse renin promoter from -365 to +16 can mediate the activation by cAMP and c-Jun in a kidney-cell dominant manner. Deletion analysis indicated that the region from -75 to -48 was responsible for the activation by cAMP. Furthermore, the core promoter region from -47 to +16 was sufficient to confer c-Jun inducibility.

The nature of fuel provision for the Na+,K(+)-ATPase in porcine vascular smooth muscle

1. The specific contributions of aerobic glycolysis and oxidative metabolism to Na+ pump activity were quantitated in porcine carotid arteries under aerobic conditions. 2. Active reaccumulation of potassium by potassium-depleted tissues could be supported by oxidative metabolism alone, anaerobic metabolism in the presence of glucose, or a combination of oxidative metabolism and aerobic glycolysis, but not under anaerobic conditions in the absence of glucose. 3. Increasing levels of potassium added to potassium-depleted arteries under aerobic conditions resulted first in stimulation of aerobic lactate release which saturated at 0.028-0.036 mumol min-1 g-1, which was then followed by a stimulation of oxidative metabolism. This behaviour is opposite to the classic Pasteur effect. 4. The dependence of potassium uptake and lactate release on the concentration of potassium added to potassium-depleted arteries ('potassium re-entry concentration') under aerobic conditions were qualitatively similar. The K0.5 (concentration at which the velocity is half-maximally activated) and Vmax (the maximum velocity) for lactate release were 1.2 +/- 0.3 mM and 0.037 mumol min-1 g-1, respectively; those for K+ uptake were 4.3 +/- 0.4 mM and 0.399 mumol min-1 g-1. 5. The stoichiometric ratio between potassium uptake and ATP as calculated from lactate release approximated theoretical values of 2:1 (assuming 1 ATP per lactate) when potassium re-entry concentrations were less than 2 mM; higher concentrations of potassium produced ratios up to 9:1. 6. Physiological pump rates, as determined by potassium efflux studies, corresponded to potassium re-entry concentrations of less than or equal to 2 mM, the same potassium re-entry concentrations where the stoichiometry between potassium transport and aerobic glycolysis approximated the theoretical ratio of 2:1. Increases in oxidative metabolism were not detected in this range, but were detected at potassium re-entry concentrations of greater than or equal to 4 mM. 7. It was concluded that at physiological Na+ pump rates, aerobic glycolytic metabolism supported the N+,K(+)-ATPase; at higher pump rates, oxidative metabolism was required for pump support as well.

Vascular oxidative metabolism under different metabolic conditions

Control of respiration in vascular smooth muscle was examined while the metabolic state of the tissue was manipulated. During KCl-induced contractures in the presence of 5 mM glucose, oxygen consumption increased by 10 nmol/per min g without any decrease in phosphocreatine (PCr) or ATP as determined by 31P-NMR indicating a control of respiration which does not involve changes in high-energy phosphates (e.g., ADP, phosphorylation potential). However, when aortae with resting tone in the absence of substrate were then provided with 5 mM 2-deoxyglucose as the sole substrate, oxygen consumption increased 7.4 nmol/min per g while PCr decreased by more than 50% (resulting in a 2-fold increase in the calculated free ADP) with no change in tension from resting tone. During a subsequent KCl induced contracture in the presence of 2-deoxyglucose, oxygen consumption increased an additional 7.2 nmol/min per g while PCr continued to decline. Therefore, at least two mechanisms of respiratory control may exist in sheep aorta, one dependent and the other independent of changes in high-energy phosphates.

Decreased renin release and constant kallikrein secretion after injection of L-NAME in isolated perfused rat kidney

A possible role of the endothelial L-arginine/NO pathway in the control of renal hemodynamics, renin release and kallikrein secretion was studied in an isolated rat kidney model perfused in a closed-circuit. NG-nitro-L-arginine methyl ester (L-NAME, 1-50 microM), an inhibitor of nitric oxide biosynthesis, caused a dose-dependent increase in perfusion pressure (PP) and a dose-dependent decrease in renal perfusate flow. Renin release was inhibited independently of a rise in PP. L-NAME did not change the urinary kallikrein secretion. These results confirm the intervention of the L-arginine/NO pathway in the vasodilation of this isolated perfused kidney model and demonstrate the inhibitory effect of L-NAME on renin release. They suggest that nitric oxide synthesis plays a role in stimulating renin release and is not involved in the regulation of urinary kallikrein secretion.