Contraction and metabolic acitivity of electrically stimulated cardiac myocytes from adult rats

Abstract

An experimental setup has been developed, which allows electrical stimulation of cardiac myocytes and simultaneous measurement of oxygen consumption, lactate production, extent of shortening and of substrate uptake. In resting cells and in cells stimulated with 120 to 480/min the oxygen consumption ranged from 25 to 100 μl/min · g_ww, with a linear relationship between rate of stimulation and oxygen consumption ($\user1{\dot VO}_{\user1{2 }}$). When using 5 mM glucose plus 2 mM pyruvate or 10 mM lactate as substrates, isoproterenol (8 · 10⁻⁸ M) augmented contraction and VO₂ at all rates of stimulation. Assuming Hook's law for passive elastic behavior for the contracting myocytes over the length change observed, a good correlation exists between the degree of cell shortening calculated from$\user1{\dot VO}_{\user1{2 }}$ per beat and the degree of contraction measured. This correlation can be used as a measure of the economy of O₂ utilization.