The effects of inhibition of oxidative phosphorylation and glycolysis on contractility and high-energy phosphate content in cultured chick heart cells.

Abstract

Cultured embryonic chick ventricular cells were exposed to various concentrations of cyanide ion to determine the relationships between graded inhibition of oxidative phosphorylation, contractile performance and high energy phosphate contents. Exposure to cyanide produced a decline in contractile amplitude (CA) of cell motion of the spontaneously beating myocytes within 30-40 s. The threshold cyanide concentration for this effect was 10-5 M, and progressive increments in cyanide concentration produced further declines in contractile amplitude to 18% of control at a cyanide concentration of 1.5 .times. 10-4 M. Control values for ATP and phosphocreatine were 28.9 .+-. 0.08 and 17.9 .+-. 0.05 nmol/mg protein, respectively, and exposure of cultured cells to cyanide produced a decline in ATP concentration within 5-10 s. At low concentrations of cyanide, the decrement in high energy phosphate content paralleled the decline in contractile function after 10 min of cyanide exposure. However, as the concentration of cyanide was increased to above 10-4 M, high energy phosphate content did not decline below 50-60% of control values, despite further decrements in amplitude of contraction. Exposure of cultured cells to 10-6 M verapamil, which abolishes mechanical activity, resulted in preservation of high energy phosphate contents in cells exposed to cyanide at concentrations less than 10-4 M. However, there was no effect of verapamil on high energy phosphate contents in the presence of higher concentrations of cyanide. Exposure of these cells to inhibitors of glycolysis, 2-deoxyglucose (20 mM), or iodoacetate (10-4 M) resulted in a decline in contractile amplitude (55% of control after 10 min of exposure to 2-deoxyglucose) that was prevented by provision of the Krebs cycle substrates, acetate or pyruvate. However, glycolytic blockade with 2-deoxyglucose in the presence of cyanide (10-4 M) and acetate, did produce further depression of contractile amplitude and high energy phosphate contents. These findings suggest that there is a quantitative relationship between the degree of depression of contractility and ATP and phosphocreatine levels only during mild-to-moderate degrees of inhibition of oxidative phosphorylation, and that negative inotropy during severe impairment of oxidative phosphorylation may preserve high energy phosphate. Energy derived from glycolysis, although not essential for maintenance of contractile function when oxidative phosphorylation is unimpeded and Krebs cycle substrate is provided, can contribute importantly to maintenance of high energy phosphate content and contractility during inhibition of oxidative phosphorylation.