Role of changes in [Ca2+]i in energy deprivation contracture.
Mechanisms of energy deprivation contracture were investigated in cultured chick embryo ventricular cells. In the presence of zero-extracellular-Na+, (choline chloride substitution)-nominal-zero-Ca2+ [( Ca2+] approximately 5 microM), exposure of ventricular cells to 1 mM cyanide (CN) and 20 mM 2-deoxyglucose (2-DG)-zero-glucose solution resulted in the development of a contracture (video motion detector) in 5.9 +/- 0.5 minutes. Early after contracture development, the resupply of extracellular Na+, in the continued presence of CN + 2-DG, resulted in a rapid partial relaxation (t1/2 = 1.9 +/- 0.3 seconds), associated with an increase in 45Ca efflux, presumably due to transsarcolemmal Ca2+ extrusion due to Na+-Ca2+ exchange. Resupply of glucose and removal of CN + 2-DG, in the continued absence of Na+, resulted in an initially slower (t1/2 = 11.6 +/- 2.5 seconds), but more complete relaxation of contracture, which was not associated with increased Ca2+ efflux. Pretreatment with 20 mM caffeine delayed the onset of contracture (9.2 +/- 1.1 minutes) and resulted in a contracture that could not be relaxed by resupply of external Na+ only. Studies using the fluorescent Ca2+ probe indo 1 demonstrated that in zero-Na+-zero-Ca2+ solutions, contracture due to CN + 2-DG was associated with an initial rise in [Ca2+]i but that this did not account for all of contracture force development. In cells exposed to CN + 2-DG in the presence of normal extracellular Na+ and Ca2+ concentrations, a small rise in [Ca2+]i was associated with initial contracture development, consistently preceding the development of a larger accelerated contracture presumably due to ATP depletion.(ABSTRACT TRUNCATED AT 250 WORDS)
Barry
W H
WH
Department of Medicine, University of Utah, School of Medicine, Salt Lake City.
Peeters
G A
GA
Rasmussen
C A
CA
Cunningham
M J
MJ
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D002642:Chick Embryo; D003486:Cyanides / Q000494:pharmacology; D003847:Deoxyglucose / Q000494:pharmacology; D004734:Energy Metabolism; D005456:Fluorescent Dyes; D007211:Indoles; D009200:Myocardial Contraction / Q000187:drug effects; D012964:Sodium / Q000494:pharmacology
D003486:Cyanides; D005456:Fluorescent Dyes; D007211:Indoles; D002110:Caffeine; D000255:Adenosine Triphosphate; D003847:Deoxyglucose; D012964:Sodium; C048960:indo-1; D002118:Calcium