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)