The relationship between contractile force and intracellular (Ca2+) in intact rat cardiac trabeculae

Analysis of the correlation between intracellular Ca2+ ((Ca2+)i) and contractile force in intact cardiac trabeculae of rat injected with fura-2 salt reveals that 0.65 plus or minus 0.19 micromoles of (Ca2+)i stimulates the steady state force-(Ca2+)i relationship during ryanodine tetanization. The Ca2+-ATPase inhibitor, cyclopiazonic acid (CPA), attenuates the rate of decay of (Ca2+)i and enables the force to reach a steady state with (Ca2+)i. However, the force-(Ca2+)i relationship is insufficient for predicting the steady state relationship during physiological twitch contractions.