Atrial natriuretic peptide stimulates Na+‐dependent Ca2+ efflux from freshly isolated adult rat cardiomyocytes

In the present study, we examined the effect of atrial natriuretic peptide (ANP) on Ca2+ efflux from freshly isolated adult rat cardiomyocytes. Rat ANP(1–28) stimulated the efflux of 45Ca2+ from the cells in a concentration‐dependent manner (10−8 M to 10−6 M). The 45Ca2+ efflux was not affected by removal of extracellular Ca2+, but was dependent on the presence of extracellular Na+. In addition, rat ANP(1–28) caused 22Na+ influx into the cells. The 45Ca2+ efflux was also stimulated by C‐type natriuretic peptide‐22 (CNP‐22), but not by rat brain natriuretic peptide‐45 (BNP‐45). It was also observed that both rat ANP(1–28) and CNP‐22 stimulated guanosine 3′,5′‐cyclic monophosphate production within the cells. These results indicate that ANP stimulates Na+‐dependent 45Ca2+ efflux from freshly isolated adult rat cardiomyocytes, probably through Na+/Ca2+ exchange, and that the stimulatory effect of ANP on Ca2+ efflux may be mediated via the natriuretic peptide receptor which has been shown to couple to guanylate cyclase. Since it is reported that Na+/Ca2+ exchange is important in calcium homeostasis within cells, ANP may play a role in the extrusion of intracellular Ca2+ from isolated adult rat cardiomyocytes.