. Altered functional coupling of coronary K ϩ channels in diabetic dyslipidemic pigs is prevented by exercise.

No abstract

1 The effects of ryanodine and caffeine on intracellular free Ca2+ concentration ([Ca2+] 5 Cells pretreated with caffeine in 0 Ca PSS, which depleted the caffeine-sensitive sarcoplasmic reticulum Ca2" store, showed no increase in [Ca24], when challenged with 10 fLM ryanodine. The ryanodine-associated increase in [Ca2+],, which was sustained in 0 Ca PSS during the 10 min ryanodine exposure in cells not pretreated with caffeine, suggests that ryanodine releases Ca2+ from the sarcoplasmic reticulum, but also inhibits Ca24 efflux.6 Intracellular free Ba2+ ([Ba24],) was measured with fura-2 microfluorometry to define further the Ca2" efflux pathway inhibited by ryanodine; specifically, Ba2+ is not transported by the Ca2" pump, but will substitute for Ca2" in Na+-Ca24 exchange. In porcine cells pretreated with caffeine in 0 Ca PSS to deplete the caffeine-sensitive sarcoplasmic reticulum Ca2+ store, depolarization with 80 mM K4 in 2 mM external Ba24 caused a 100 ± 6% increase in fura-2 fluorescence ([Ba2+]

SUMMARY1. We tested the hypothesis that the sarcoplasmic reticulum (SR) buffers (attenuates) the increase in averaged myoplasmic free [Ca2+] (Caim)

Heterogeneity of vascular responses to physiological and pharmacological stimuli has been demonstrated throughout the coronary circulation. Typically, this heterogeneity is based on vessel size. Although the cellular mechanisms for this heterogeneity are unknown, one plausible factor may be heterogeneous distribution of ion channels important in regulation of vascular tone. Because of the importance of voltage-gated Ca2+ channels in regulation of vascular tone, we hypothesized that these channels would be unequally distributed throughout the coronary arterial bed. To test this hypothesis, voltage-gated Ca2+current was measured in smooth muscle from conduit arteries (>1.0 mm), small arteries (200–250 μm), and large arterioles (75–125 μm) of miniature swine using whole cell voltage-clamp techniques. With 2 mM Ca2+ or 10 mM Ba2+ as charge carrier, voltage-gated Ca2+ current density was inversely related to arterial diameter, i.e., large arterioles > small arteries > conduit. Peak inward currents (10 mM Ba2+) were increased ∼2.5- and ∼1.5-fold in large arterioles and small arteries, respectively, compared with conduit arteries (−5.58 ± 0.53, −3.54 ± 0.34, and −2.26 ± 0.31 pA/pF, respectively). In physiological Ca2+ (2 mM), small arteries demonstrated increased inward current at membrane potentials within the physiological range for vascular smooth muscle (as negative as −40 mV) compared with conduit arteries. In addition, cells from large arterioles showed a negative shift in the membrane potential for half-maximal activation compared with small and conduit arteries (−13.23 ± 0.88, −6.22 ± 1.35, and −8.62 ± 0.81 mV, respectively; P < 0.05). Voltage characteristics and dihydropyridine sensitivity identified this Ca2+ current as predominantly L-type current in all arterial sizes. We conclude that L-type Ca2+ current density is inversely related to arterial diameter within the coronary arterial vasculature. This heterogeneity of Ca2+ current density may provide, in part, the basis for functional heterogeneity within the coronary circulation.

Expression of polycystin-1 enhances endoplasmic reticulum calcium uptake and decreases capacitative calcium entry in ATP-stimulated MDCK cells.

Exercise training attenuates coronary smooth muscle phenotypic modulation and nuclear Ca 2ϩ signaling. Am J Physiol Heart Circ Physiol 283: H2397-H2410, 2002. First published July 26. 2002 10.1152/ajpheart.00371. 2001.-Physical inactivity is an independent risk factor for coronary heart disease, yet the mechanism(s) of exerciserelated 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 2ϩ . 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 Ͻ 0.01). EX decreased single cell peak endothelin-1-induced cytosolic Ca 2ϩ responses compared with SED by 16% and peak nuclear Ca 2ϩ responses by 33% (P Ͻ 0.05), as determined by confocal microscopy. On the basis of these results, we hypothesized that sarco(endo)plasmic reticulum Ca 2ϩ -ATPase (SERCA) and intracellular Ca 2ϩ stores in native smooth muscle are spatially localized to dissociate cytosolic Ca 2ϩ and nuclear Ca 2ϩ . 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 2ϩ regulation, possibly via SERCA, which may be one mechanism by which coronary smooth muscle cells from EX are less responsive to mitogeninduced phenotypic modulation.endothelin-1; sarco(endo)plasmic reticulum Ca 2ϩ -ATPase; electron microscopy; fluorescence microscopy; swine SUBSTANTIAL EVIDENCE EXISTS supporting the role of chronic endurance exercise training in reducing the incidence of coronary heart disease (6, 39), yet the mechanism(s) of exercise-related cardioprotection remains unknown. Coronary heart disease can be subdivided into two general categories: diseases of coronary vessel tone, i.e., acute vasospasm and hypertension, and diseases of vessel injury, i.e., atherosclerosis. Several studies from our laboratory have addressed mechanisms associated with exercise training adaptations (for reviews, see Refs. 10 and 43). However, there are few studies (48) addressing exercise-related coronary smooth muscle adaptations and their relationship to resistance to the development of vascular disease.Atherosclerosis is a complex disease involving an inflammatory-fibroproliferative response that develops from various forms of insult to the endothelium and smooth muscle cells of the artery (38). The phenotypic modulation of smooth muscle cells plays a key role in the development of atherosclerosis and is characterized in part by increased DNA synthesis (34); altered functional receptor expression, including receptors involved in growth factor signaling (29); and subcellular/ ultrastructure morphology (35,38,47). In cells from diseased vessels, Ca 2ϩ regulation is also altered (18) and implicated in increased vessel tone and vasospasm (27, 28). We recently reported that localized Ca 2ϩ signaling...

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 μm), and large arterioles (75–150 μm) 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.