Modulation of cAMP: mechanism for positive inotropic action.

Modulation of intracellular cAMP in cardiac cells results in a positive inotropic effect. This effect is achieved by increasing intracellular cAMP, via a variety of ways, which leads to the phosphorylation of proteins in the sarcolemma, sarcoplasmic reticulum, and contractile filaments. This phosphorylation alters calcium metabolism in the cell to effect an increase in the influx of extracellular calcium, an increase in sarcoplasmic reticulum uptake of calcium, and an altered sensitivity of the contractile proteins to calcium. These changes in cellular metabolism of calcium effect an increase in cardiac contractility which is associated with an increase in rate of both contraction and relaxation.