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D K Bowles

Publications and source records attributed to D K Bowles.

At least 19 recordsLinked to original sources
PubMed2006

Upregulation of intermediate-conductance Ca2+-activated K+ channel (IKCa1) mediates phenotypic modulation of coronary smooth muscle.

A hallmark of smooth muscle cell (SMC) phenotypic modulation in atherosclerosis and restenosis is suppression of SMC differentiation marker genes, proliferation, and migration. Blockade of intermediate-conductance Ca(2+)-activated K(+) channels (IKCa1) has been shown to inhibit restenosis after carotid balloon injury in the rat; however, whether IKCa1 plays a role in SMC phenotypic modulation is unknown. Our objective was to determine the role of IKCa1 channels in regulating coronary SMC phenotypic modulation and migration. In cultured porcine coronary SMCs, platelet-derived growth factor-BB (PDGF-BB) increased TRAM-34 (a specific IKCa1 inhibitor)-sensitive K(+) current 20-fold; increased IKCa1 promoter histone acetylation and c-jun binding; increased IKCa1 mRNA approximately 4-fold; and potently decreased expression of the smooth muscle differentiation marker genes smooth muscle myosin heavy chain (SMMHC), smooth muscle alpha-actin (SMalphaA), and smoothelin-B, as well as myocardin. Importantly, TRAM-34 completely blocked PDGF-BB-induced suppression of SMMHC, SMalphaA, smoothelin-B, and myocardin and inhibited PDGF-BB-stimulated migration by approximately 50%. Similar to TRAM-34, knockdown of endogenous IKCa1 with siRNA also prevented the PDGF-BB-induced increase in IKCa1 and decrease in SMMHC mRNA. In coronary arteries from high fat/high cholesterol-fed swine demonstrating signs of early atherosclerosis, IKCa1 expression was 22-fold higher and SMMHC, smoothelin-B, and myocardin expression significantly reduced in proliferating vs. nonproliferating medial cells. Our findings demonstrate that functional upregulation of IKCa1 is required for PDGF-BB-induced coronary SMC phenotypic modulation and migration and support a similar role for IKCa1 in coronary SMC during early coronary atherosclerosis.

Actins↗
PubMed2005

Isoform-specific modulation of coronary artery PKC by glucocorticoids.

Glucocorticoids (GC) exert diverse cellular effects in response to both acute and chronic stress, the functional consequences of which have been implicated in the development of cardiovascular pathology such as hypertension and atherosclerosis. However, the mechanisms by which GCs activate divergent signaling pathways are poorly understood. The present study examined the direct effects of natural (cortisol) and synthetic (dexamethasone) GCs on protein kinase C (PKC) isoform expression in coronary arteries. Porcine right coronary arteries were treated in vitro for 18 h in the presence and absence of either dexamethasone (10, 100, or 500 nM) or cortisol (50, 125, 250, or 500 nM). PKC isoform levels and subcellular distribution were determined by immmunoblotting of whole cell homogenates and immunocytofluorescence using PKC-alpha, -betaII, -epsilon, -delta, and -zeta specific antibodies. Dexamethasone caused a approximately 4-fold increase in PKC-alpha, a approximately 2.5-fold increase in PKC-betaII, and a 2-fold increase in PKC-epsilon (p<0.05). In contrast, dexamethasone had no effect on PKC-delta or PKC- zeta levels. Dexamethasone also caused an increase in the activity of PKC-alpha (285%), -betaII (170%), and -epsilon (210%). Cortisol produced similar effects on PKC isoform expression. Confocal microscopy revealed that while dexamethasone altered localization patterns for PKC-alpha, -betaII and -epsilon, no such effect was observed for PKC-delta or PKC-zeta. The stimulatory effects of dexamethasone and cortisol on coronary PKC levels and translocation were prevented by the GC receptor (GR) blocker, RU486. These results demonstrate, for the first time, that GCs modulate coronary PKC expression and subcellular distribution in an isoform-specific manner through a GR-dependent mechanism.

Animals↗
PubMed2004

Hypercholesterolemia abolishes voltage-dependent K+ channel contribution to adenosine-mediated relaxation in porcine coronary arterioles.

Hypercholesterolemic patients display reduced coronary flow reserve in response to adenosine infusion. We previously reported that voltage-dependent K+ (Kv) channels contribute to adenosine-mediated relaxation of coronary arterioles isolated from male miniature swine. For this study, we hypothesized that hypercholesterolemia attenuates Kv channel contribution to adenosine-induced vasodilatation. Pigs were randomly assigned to a control or high fat/high cholesterol diet for 20-24 wk, and then killed. After completion of the experimental treatment, arterioles (approximately 150 microm luminal diameter) were isolated from the left-ventricular free wall near the apical region of the heart, cannulated, and pressurized at 40 mmHg. Adenosine-mediated relaxation was significantly attenuated in both endothelium-intact and -denuded arterioles from hypercholesterolemic compared with control animals. The classic Kv channel blocker, 4-aminopyridine (1 mM), significantly attenuated adenosine-mediated relaxation in arterioles isolated from control but not hypercholesterolemic animals. Furthermore, the nonselective K+ channel blocker, tetraethylammonium (TEA; 1 mM) significantly attenuated adenosine-mediated relaxation in arterioles from control but not hypercholesterolemic animals. In additional experiments, coronary arteriolar smooth muscle cells were isolated, and whole cell Kv currents were measured. Kv currents were significantly reduced (approximately 15%) in smooth muscle cells from hypercholesterolemic compared with control animals. Furthermore, Kv current sensitive to low concentrations of TEA was reduced (approximately 45%) in smooth muscle cells from hypercholesterolemic compared with control animals. Our data indicate that hypercholesterolemia abolishes Kv channel contribution to adenosine-mediated relaxation in coronary arterioles, which may be attributable to a reduced contribution of TEA-sensitive Kv channels in smooth muscle of hypercholesterolemic animals.

Adenosine↗
PubMed2004

L-type voltage-gated Ca2+ channels modulate expression of smooth muscle differentiation marker genes via a rho kinase/myocardin/SRF-dependent mechanism.

Vascular smooth muscle cell (SMC) contraction is mediated in part by calcium influx through L-type voltage-gated Ca2+ channels (VGCC) and activation of the RhoA/Rho kinase (ROK) signaling cascade. We tested the hypothesis that Ca2+ influx through VGCCs regulates SMC differentiation marker expression and that these effects are dependent on RhoA/ROK signaling. Depolarization-induced activation of VGCCs resulted in a nifedipine-sensitive increase in endogenous smooth muscle myosin heavy chain (SMMHC) and SM alpha-actin expression and CArG-dependent promoter activity, as well as c-fos promoter activity. The ROK inhibitor, Y-27632, prevented depolarization-induced increase in SMMHC/SM alpha-actin but had no effect on c-fos expression. Conversely, the Ca2+/calmodulin-dependent kinase inhibitor, KN93, prevented depolarization-induced increases in c-fos expression with no effect on SMMHC/SM alpha-actin. Depolarization increased expression of myocardin, a coactivator of SRF that mediates CArG-dependent transcription of SMC marker gene promoters containing paired CArG cis regulatory elements (SMMHC/SM alpha-actin). Both nifedipine and Y-27632 prevented the depolarization-induced increase in myocardin expression. Moreover, short interfering RNA (siRNA) specific for myocardin attenuated depolarization-induced SMMHC/SM alpha-actin transcription. Chromatin immunoprecipitation (ChIP) assays revealed that depolarization increased SRF enrichment of the CArG regions in the SMMHC, SM alpha-actin, and c-fos promoters in intact chromatin. Whereas Y-27632 decreased basal and depolarization-induced SRF enrichment in the SMMHC/SM alpha-actin promoter regions, it had no effect of SRF enrichment of c-fos. Taken together, these results provide evidence for a novel mechanism whereby Ca2+ influx via VGCCs stimulates expression of SMC differentiation marker genes through mechanisms that are dependent on ROK, myocardin, and increased binding of SRF to CArG cis regulatory elements.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed2004

Endogenous testosterone increases L-type Ca2+ channel expression in porcine coronary smooth muscle.

Evidence indicates that gender and sex hormonal status influence cardiovascular physiology and pathophysiology. We recently demonstrated increased L-type voltage-gated Ca2+ current (ICa,L) in coronary arterial smooth muscle (CASM) of male compared with female swine. The promoter region of the L-type voltage-gated Ca2+ channel (VGCC) (Cav1.2) gene contains a hormone response element that is activated by testosterone. Thus the purpose of the present study was to determine whether endogenous testosterone regulates CASM ICa,L through regulation of VGCC expression and activity. Sexually mature male and female Yucatan swine (7-8 mo; 35-45 kg) were obtained from the breeder. Males were left intact (IM, n=8), castrated (CM, n=8), or castrated with testosterone replacement (CMT, n=8; 10 mg/day Androgel). Females remained gonad intact (n=8). In right coronary arteries, both Cav1.2 mRNA and protein were greater in IM compared with intact females. Cav1.2 mRNA and protein were reduced in CM compared with IM and restored in CMT. In isolated CASM, both peak and steady-state ICa were reduced in CM compared with IM and restored in CMT. In males, a linear relationship was found between serum testosterone levels and ICa. In vitro, both testosterone and the nonaromatizable androgen, dihydrotestosterone, increased Cav1.2 expression. Furthermore, this effect was blocked by the androgen receptor antagonist cyproterone. We conclude that endogenous testosterone is a primary regulator of Cav1.2 expression and activity in coronary arteries of males.

Animals↗
PubMed2004

Hypercholesterolemia inhibits L-type calcium current in coronary macro-, not microcirculation.

Hypercholesterolemia (HC) is a mary risk factor for the development of coronary heart disease. Coronary ion regulation, especially calcium, is thought to be important in coronary heart disease development; however, the influence of high dietary fat and cholesterol on coronary arterial smooth muscle (CASM) ion channels is unknown. The purpose of this study was to determine the effect of diet-induced HC on CASM voltage-gated calcium current (I(Ca)). Male miniature swine were fed a high-fat, high-cholesterol diet (40% kcal fat, 2% wt cholesterol) for 20-24 wk, resulting in elevated serum total and low-density lipoprotein cholesterol. Histochemistry indicated early atherosclerosis in large coronary arteries. CASM were isolated from the right coronary artery (>1.0 mm ID), small arteries ( approximately 200 microm), and large arterioles ( approximately 100 microm). I(Ca) was determined by whole cell voltage clamp. L-type I(Ca) was reduced approximately 30% by HC compared with controls in the right coronary artery (-5.29 +/- 0.42 vs. -7.59 +/- 0.41 pA/pF) but not the microcirculation (small artery, -8.39 +/- 0.80 vs. -10.13 +/- 0.60; arterioles, -10.78 +/- 0.93 vs. -11.31 +/- 0.95 pA/pF). Voltage-dependent activation was unaffected by HC in both the macro- and microcirculation. L-type voltage-gated calcium channel (Ca(v)1.2) mRNA and membrane protein levels were unaffected by HC. Inhibition of I(Ca) by HC was reversed in vitro by the cholesterol scavenger methyl-beta-cyclodextrin and mimicked in control CASM by incubation with the cholesterol donor cholesterol:methyl-beta-cyclodextrin. These data indicate that CASM L-type I(Ca) is decreased in large coronary arteries in early stages of atherosclerosis, whereas I(Ca) in the microcirculation is unaffected. The inhibition of calcium channel activity in CASM of large coronary arteries is likely due to increases in membrane free cholesterol.

Animals↗
PubMed2003

Alterations in PKC signaling underlie enhanced myogenic tone in exercise-trained porcine coronary resistance arteries.

The intracellular mechanisms underlying enhanced myogenic contraction (MC) in coronary resistance arteries (CRAs) from exercise-trained (EX) pigs have not been established. The purpose of this study was to test the hypothesis that exercise-induced alterations in protein kinase C (PKC) signaling underlie enhanced MC. Furthermore, we sought to determine whether modulation of intracellular Ca(2+) signaling by PKC underlies enhanced MC in EX animals. Male Yucatan miniature swine were treadmill trained (n = 7) at approximately 75% of maximal O(2) uptake for 16 wk (6 miles/h, 60 min) or remained sedentary (SED, n = 6). Diameter measurements in response to intraluminal pressure (60, 75, and 90 cmH(2)O) or 60 mM KCl were determined in single, cannulated CRAs ( approximately 100 microm ID) with and without the PKC inhibitor chelerythrine (CE, 1 microM). Confocal imaging of Ca(2+) signaling [myogenic Ca(2+) (Ca(m))] was also performed in CRAs of similar internal diameter after abluminal loading of the Ca(2+) indicator dye fluo 4 (1 microM, 37 degrees C, 30 min). We observed significantly greater MC in CRAs isolated from EX than from SED animals at 90 cmH(2)O, as well as greater reductions in MC after CE at all pressures studied. At intraluminal pressures of 75 and 90 cmH(2)O, CE produced greater decreases in Ca(m) in CRAs from EX than from SED animals (64% vs. 25%, P < 0.05). Inhibition of KCl constriction and Ca(m) by CE was also greater in EX animals (P < 0.05). Western blotting revealed significant increases in Ca(2+)-dependent PKC-alpha ( approximately 50%) but not Ca(2+)-independent PKC-epsilon levels in CRAs isolated from EX animals (P < 0.05). We also observed significant group differences in phosphorylated PKC-alpha levels. Finally, voltage-gated Ca(2+) current (VGCC) was effectively blocked by CE, bisindolylmaleimide, and staurosporine in isolated smooth muscle cells from CRAs, providing evidence for a mechanistic link between VGCCs and PKC in our experimental paradigm. These results suggest that enhanced MC in CRAs from EX animals involves PKC-dependent modulation of intracellular Ca(2+), including regulation of VGCCs.

Animals↗
PubMed2003

Coronary smooth muscle adaptation to exercise: does it play a role in cardioprotection?

Substantial evidence exists supporting the role of chronic exercise in reducing the incidence and severity of coronary vascular disease. Physical inactivity is an independent risk factor for coronary heart disease suggesting that the cardioprotective effect of exercise is due, in part, to an intrinsic adaptation within the coronary vasculature. Surprisingly, a paucity of information exists regarding the intrinsic cellular changes within the coronary vasculature associated with exercise training and even less is known regarding the effect of physical activity on long-term phenotypic modulation of coronary smooth muscle (CSM). The purpose of this symposium is to provide a concise update on the current knowledge regarding CSM adaptation to exercise training and the potential for these adaptations to contribute to exercise-induced cardioprotection. The potential role of CSM in exercise-induced cardioprotection will be approached from two perspectives. First, endurance exercise training effects on the regulation of coronary vasomotor tone via changes in CSM calcium regulation will be reviewed, i.e. short-term functional adaptation. Secondly, we will discuss potential long-term consequences of this altered calcium regulation, i.e. exercise-induced phenotypic modulation of CSM. We propose that exercise training alters CSM intracellular calcium regulation to reduce Ca2+-dependent activation of the contractile apparatus and Ca2+-dependent gene transcription and increase activation of sarcolemmal potassium channels. The overall effect is to increase the gain of the vasomotor system and maintain a stable, contractile CSM phenotype.

Adaptation, Physiological↗
PubMed2002

Exercise training attenuates coronary smooth muscle phenotypic modulation and nuclear Ca2+ signaling.

Physical inactivity is an independent risk factor for coronary heart disease, yet the mechanism(s) of exercise-related cardioprotection remains unknown. We tested the hypothesis that coronary smooth muscle after exercise training would have decreased mitogen-induced phenotypic modulation and enhanced regulation of nuclear Ca(2+). Yucatan swine were endurance exercise trained (EX) on a treadmill for 16-20 wk. EX reduced endothelin-1-induced DNA content by 40% compared with sedentary (SED) swine (P < 0.01). EX decreased single cell peak endothelin-1-induced cytosolic Ca(2+) responses compared with SED by 16% and peak nuclear Ca(2+) responses by 33% (P < 0.05), as determined by confocal microscopy. On the basis of these results, we hypothesized that sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) and intracellular Ca(2+) stores in native smooth muscle are spatially localized to dissociate cytosolic Ca(2+) and nuclear Ca(2+). Subcellular localization of SERCA in living and fixed cells revealed a distribution of SERCA near the sarcolemma and on the nuclear envelope. These results show that EX enhances nuclear Ca(2+) regulation, possibly via SERCA, which may be one mechanism by which coronary smooth muscle cells from EX are less responsive to mitogen-induced phenotypic modulation.

Animals↗
PubMed2001

Hydrogen peroxide activates Na(+)-dependent Ca(2+) influx in coronary endothelial cells.

The purpose of the present study was to examine the effect of short duration H(2)O(2) exposure on coronary artery endothelial cell [Ca(2+)](i) regulation. Freshly dispersed cells from porcine coronary artery were exposed to H(2)O(2) (300 micromol/L) for 3 min while monitoring [Ca(2+)](i) using fura-2 microfluorometry. H(2)O(2) increased [Ca(2+)](i) from 0.86 +/- 0.03 to 2.19 +/- 0.41 ratio units at 3 min of H(2)O(2) (P < 0.05). Intracellular Ca(2+) remained elevated 3 min following removal of H(2)O(2), yet H(2)O(2) had no effect on the subsequent [Ca(2+)](i) response to bradykinin (0.1 micromol/L). The H(2)O(2)-induced [Ca(2+)](i) increase was completely abolished either by removal of extracellular Ca(2+) or lowering extracellular Na(+). Cells exposed to the Na(+) ionophore, monensin, showed an increase in [Ca(2+)](i) with a time course similar to that seen with H(2)O(2). Furthermore, H(2)O(2)-induced Ca(2+) influx was not attenuated by either Ni(2+) (300 micromol/L) or econazole (10 micromol/L), excluding Ca(2+) influx via the agonist-sensitive pathway. Thus, in coronary arterial endothelial cells, H(2)O(2) increases Ca(2+) influx in an extracellular Na(+)-dependent manner via an agonist-insensitive pathway.

Animals↗
PubMed2001

Gender influences coronary L-type Ca(2+) current and adaptation to exercise training in miniature swine.

Endurance exercise training increases smooth muscle L-type Ca(2+) current density in both resistance and proximal coronary arteries of female miniature swine. The purpose of the present study was to determine 1) whether gender differences exist in coronary smooth muscle (CSM) L-type Ca(2+) current density and 2) whether endurance training in males would demonstrate a similar adaptive response as females. Proximal, conduit (approximately 1.0 mm), and resistance [~200 microm (internal diameter)] coronary arteries were obtained from sedentary and treadmill-trained swine of both sexes. CSM were isolated by enzymatic digestion (collagenase plus elastase), and voltage-gated Ca(2+)-channel current (I(Ca)) was determined by using whole cell voltage clamp during superfusion with 75 mM tetraethylammonium chloride and 10 mM BaCl(2). Current-voltage relationships were obtained at test potentials from -60 to 70 mV from a holding potential of -80 mV, and I(Ca) was normalized to cell capacitance (pA/pF). Endurance treadmill training resulted in similar increases in heart weight-to-body weight ratio, endurance time, and skeletal muscle citrate synthase activity in male and female swine. I(Ca) density was significantly greater in males compared with females in both conduit (-7.57 +/- 0.58 vs. -4.14 +/- 0.47 pA/pF) and resistance arteries (-11.25 +/- 0.74 vs. -6.49 +/- 0.87 pA/pF, respectively). In addition, voltage-dependent activation of I(Ca) in resistance arteries was shifted to more negative membrane potentials in males. Exercise training significantly increased I(Ca) density in both conduit and resistance arteries in females (-7.01 +/- 0.47 and -9.73 +/- 1.13 pA/pF, respectively) but had no effect in males (-8.61 +/- 0.50 and -12.04 +/- 1.07 pA/pF, respectively). Thus gender plays a significant role in determining both the magnitude and voltage dependence of I(Ca) in CSM and the adaptive response of I(Ca) to endurance training.

Adaptation, Physiological↗
PubMed2000

Enhanced L-type Ca2+ channel current density in coronary smooth muscle of exercise-trained pigs is compensated to limit myoplasmic free Ca2+ accumulation.

We hypothesized that enhanced voltage-gated Ca2+ channel current (VGCC) density in coronary smooth muscle cells of exercise-trained miniature Yucatan pigs is compensated by other cellular Ca2+ regulatory mechanisms to limit net myoplasmic free Ca2+ accumulation. Whole-cell voltage clamp experiments demonstrated enhanced VGCC density in smooth muscle cells freshly dispersed from coronary arteries of exercise-trained vs. sedentary animals. In separate experiments using fura-2 microfluorometry, we measured depolarization-induced (80 mM KCl) accumulation of myoplasmic free Ba2+ and free Ca2+. Both maximal rate and net accumulation of free Ba2+ in response to membrane depolarization were increased in smooth muscle cells isolated from exercise-trained pigs, consistent with an increased VGCC density. Depolarization also produced an enhanced maximal rate of free Ca2+ accumulation in cells of exercise-trained pigs; however, net accumulation of free Ca2+ was not significantly increased suggesting enhanced Ca2+ influx was compensated to limit net free Ca2+ accumulation. Inhibition of sarco-endoplasmic reticulum Ca2+-transporting ATPase (SERCA; 10 microM cyclopiazonic acid) and/or sarcolemmal Na+-Ca2+ exchange (low extracellular Na+) suggested neither mechanism compensated the enhanced VGCC in cells of exercise-trained animals. Local Ca2+-dependent inactivation of VGCC, assessed by buffering myoplasmic Ca2+ with EGTA in the pipette and using Ca2+ and Ba2+ as charge carriers, was not different between cells of sedentary and exercise-trained animals. Our findings indicate that increased VGCC density is compensated by other cellular Ca2+ regulatory mechanisms to limit net myoplasmic free Ca2+ accumulation in smooth muscle cells of exercise-trained animals. Further, SERCA, Na+-Ca2+ exchange and local Ca2+-dependent inactivation of VGCC do not appear to function as compensatory mechanisms. Additional potential compensatory mechanisms include Ca2+ extrusion via plasma membrane Ca2+-ATPase, mitochondrial uptake, myoplasmic Ca2+-binding proteins and other sources of VGCC inactivation.

Animals↗
PubMed2000

Coronary smooth muscle and endothelial adaptations to exercise training.

Exercise training produces complex changes in intrinsic control of coronary vascular resistance. In smooth muscle, adaptations that alter Ca2+ regulation seem central, including changes in the function of sarcolemmal K+ and L-type Ca2+ channels and the sarcoplasmic reticulum. Exercise training also increases the ability of the endothelium to release vasoactive factors, with increased expression and activity of endothelial cell nitric oxide synthase playing a key role.

Adaptation, Physiological↗
PubMed1998

Exercise training-induced adaptations in the coronary circulation.

Aerobic exercise training induces an increase in coronary blood flow capacity that is associated with altered control of coronary vascular resistance and, therefore, coronary blood flow. The relative importance of metabolic, myogenic, endothelium-mediated, and neurohumoral control systems varies throughout the coronary arterial tree, and these control systems contribute in parallel to regulating coronary vascular resistance to differing degrees at each level in the coronary arterial tree. In addition to this nonuniformity of the relative importance of vascular control systems in the coronary arterial tree, it appears that exercise training-induced adaptations are also distributed spatially, in a nonuniform manner throughout the coronary tree. As a result, it is necessary to examine training-induced adaptations throughout the coronary arterial tree. Adaptations in endothelium-mediated control play a role in training-induced changes in control of coronary vascular resistance, and there is evidence that the effects of training may be different in large coronary arteries than in the microcirculation. Also, there is evidence that the mode, frequency, and intensity of exercise training bouts and duration of training may influence the adaptive changes in endothelial function. Exercise training has also been shown to induce changes in responses of coronary vascular smooth muscle to vasoactive agents and alterations in the cellular-molecular control of intracellular Ca2+ in coronary vascular smooth muscle of conduit coronary arteries and to enhance myogenic reactivity of coronary resistance arteries. Exercise training also appears to have different effects on vascular smooth muscle in large coronary arteries than in the microcirculation. For example, adenosine sensitivity is increased in conduit coronary arteries and large resistance arteries after training but is not altered in small coronary resistance arteries of trained animals. Although much remains to be studied, evidence clearly indicates that chronic exercise alters the phenotype of coronary endothelial and vascular smooth muscle cells and that plasticity of these cells plays a role in adaptation of the cardiovascular system in exercise training.

Acetylcholine↗
PubMed1998

Exercise training increases L-type calcium current density in coronary smooth muscle.

Exercise training produces numerous adaptations in the coronary circulation, including an increase in coronary tone, both in conduit and resistance arteries. On the basis of the importance of voltage-gated Ca2+ channels (VGCC) in regulation of vascular tone, we hypothesized that exercise training would increase VGCC current density in coronary smooth muscle. To test this hypothesis, VGCC current was compared in smooth muscle from conduit arteries (>1.0 mm), small arteries (200-250 micrometer), and large arterioles (75-150 micrometer) from endurance-trained (Ex) or sedentary miniature swine (Sed). After 16-20 wk of treadmill training, VGCC current was determined using whole cell voltage-clamp techniques. In both Ex and Sed, VGCC current density was inversely related to arterial diameter, i.e., large arterioles > small arteries > conduit arteries. Exercise training increased peak inward currents approximately twofold in smooth muscle from all arterial sizes compared with those from Sed (large arteriole, -12.52 +/- 2.05 vs. -5.74 +/- 0.99 pA/pF; small artery, -6.20 +/- 0.97 vs. -3.18 +/- 0.44 pA/pF; and conduit arteries, -4.22 +/- 0.30 vs. -2.41 +/- 0.55 pA/pF; 10 mM Ba2+ external). Dihydropyridine sensitivity, voltage dependence, and inactivation kinetics identified this Ca2+ current to be L-type current in all arterial sizes from both Sed and Ex. Furthermore, peak VGCC current density was correlated with treadmill endurance in all arterial sizes. We conclude that smooth muscle L-type Ca2+ current density is increased within the coronary arterial bed by endurance exercise training. This increased VGCC density may provide an important mechanistic link between functional and cellular adaptations in the coronary circulation to exercise training.

Animals↗
PubMed1998

Exercise training increases K+-channel contribution to regulation of coronary arterial tone.

The present study examined whether regulation of coronary tone in conduit arteries (>1.0 mm ID) is altered by exercise training. Yucatan miniature swine were treadmill trained for 16-20 wk (Ex) and compared with sedentary counterparts (Sed). Endothelium-denuded arterial rings were stretched to optimal length and allowed to equilibrate for 60 min. Inhibition of either Ca2+-activated channels [1 mM tetraethylammonium (TEA) or 10 nM iberiotoxin (IBTX)] or voltage-dependent K+ channels [1 mM 4-aminopyridine (4-AP)] significantly increased resting tension in both groups; however, the effect of all K+-channel blockers was greater in Ex. Addition of 1 mM sodium nitroprusside reduced resting tension in both groups, confirming the presence of active basal tone; however, sodium nitroprusside-sensitive tone was increased approximately twofold in Ex compared with Sed group. Perforated patch-clamp experiments on isolated smooth muscle cells demonstrated no effect of exercise training on whole cell TEA-sensitive, 4-AP-sensitive, or basal K+ current. Similarly, whereas TEA, 4-AP, and IBTX all decreased resting membrane potential, there was no difference in depolarization between groups. The greater effect of TEA on resting tension in Ex could be mimicked in Sed by addition of the Ca2+-channel agonist BAY K 8644. In conclusion, the greater response to K+-channel blockers after exercise training is consistent with an increased contribution of K+ channels to regulation of basal tone in conduit coronary arteries. The lack of an effect of training on K+ current characteristics or membrane potential responses in isolated cells suggests that a requisite factor for enhanced K+-channel activation in arteries from Ex, possibly stretch, is absent in isolated cells.

4-Aminopyridine↗
PubMed1997

Myocardial injury after hypoxia in immature, adult and aged rats.

We evaluated the abilities of isolated perfused hearts from immature (IM) (2.5-3 months), ADULT (11-13 months) and OLD (24-26 months) Fischer 344 rats to tolerate and recover from oxygen deprivation. Hearts were perfused at 60 mmHg for a 30-minute prehypoxic period with oxygenated buffer supplemented with 10 mM glucose (+insulin) and 2 mM acetate, then 30 minutes with substrate-free, hypoxic buffer gassed with 95% N2:5% CO2, and finally reoxygenated for an additional 45 minutes with the same buffer used during the prehypoxic period. During prehypoxia, all groups were similar in ventricular mechanical function, glycogen content, high-energy phosphates (HEP), reduced glutathione (GSH), Ca+2 content, and mitochondrial state 3 rates. At the end of the hypoxic period, glycogen levels were similar and almost completely depleted in all groups, HEP were lower (p < 0.05) in ADULT vs other groups, mitochondrial state 3 rates were decreased (24%, p < 0.05) only in ADULT, and GSH was depleted by 34% in IM vs only 13% in OLD (p < 0.05). After 45 minutes of reoxygenation, IM and OLD had recovered 48% and 45% of their respective prehypoxic function which was two-fold greater than the 23% recovery by ADULT. Loss of cytosolic enzymes, an indicator of sarcolemmal damage, was estimated by measuring lactate dehydrogenase (LDH) release. LDH release and Ca+2 content during reoxygenation in IM were only about half of that observed in ADULT or OLD. We conclude that immature and aged hearts tolerate and recover from hypoxia better than hearts from adults, and that the sarcolemmal membranes of immature rat hearts are less susceptible to damage from hypoxic stress than those of either older group.

Aging↗