Influence of positive inotropic agents on intracellular calcium transients. Part I. Normal rat heart.

This study, which was designed to evaluate the effects of positive inotropic agents on intracellular calcium transients ([Ca2+]i), is the first to analyze calcium transients in the whole heart. The positive inotropic agents that augment intracellular cyclic adenosine monophosphate (cAMP) (dibutyryl cAMP, amrinone, and isoproterenol) caused an increase in developed pressure and [Ca2+]i transients and a decrease in diastolic [Ca2+]i. On the other hand, the glycoside digoxin and the alpha-adrenoceptor agents, phenylephrine and dobutamine, also caused an increase in [Ca2+]i transients and developed pressure. However, unlike the agents that increase [cAMP]i, they induced an elevation in diastolic [Ca2+]i. With all the positive inotropic agents, developed pressure increased commensurately with the percentage changes in amplitude of the [Ca2+]i transients.