Calcium buffering in coronary smooth muscle after chronic occlusion and exercise training

Joyce J. Jones, Nancy J. Dietz, Cristine L. Heaps, Janet L. Parker, Michael Sturek

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

Objective: Exercise promotes "sarcoplasmic reticulum (SR) Ca2+ unloading" in porcine coronary smooth muscle, resulting in decreased agonist-induced Ca2+ release. We studied Ca2+ handling in healthy, non-occluded right coronary artery cells from hearts chronically occluded at the circumflex artery. Methods: Myoplasmic free Ca2+ (Cam) was assessed with fura-2 in cells from sedentary (n=8) and aerobically exercise-trained (n=6) female Yucatan pigs after 6-month circumflex artery ameroid occlusion (OCC) and in cells from non-occluded, sedentary pigs (SED, n=5). First, Ca influx was induced by 80 mM KCl depolarization (priming step) followed by 5 mM caffeine to elicit maximal Ca2+ release and depletion. The SR was Ca-loaded again by depolarization and then exposed to caffeine after 2- or 11-min recovery to compare SR Ca2+ unloading. Results: Baseline Cam, caffeine-induced peak Cam, and depolarization-induced maximum Cam were decreased, and depolarization-induced time-to-half-maximum was increased in OCC vs. SED pigs, suggesting a tonic Ca2+ buffering (lowering) effect of occlusion. Exercise did not alter these effects. SR Ca2+ unloading occurred only in SED, as evidenced by decreased caffeine-induced Ca2+ release after 11 min of recovery, and was inhibited by low extracellular Na+. Conclusions: SR Ca2+ unloading can be demonstrated in coronary smooth muscle from sedentary pigs using a novel SR Ca2+ unloading protocol, and Ca2+ unloading partly depends on Na+-Ca2+ exchange activity. Furthermore, SR Ca2+ unloading in cells from non-occluded right coronary arteries of chronically circumflex-occluded pig hearts was not altered by exercise, perhaps due to enhanced tonic Ca2+ extrusion versus cells from normal, sedentary animals.

Original languageEnglish (US)
Pages (from-to)359-367
Number of pages9
JournalCardiovascular research
Volume51
Issue number2
DOIs
StatePublished - 2001

Keywords

  • Calcium (cellular)
  • Collateral circulation
  • Coronary circulation
  • Coronary disease
  • Na/Ca-exchanger
  • SR (function)

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

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