Stretch-dependent regulation of atrial peptide synthesis and secretion in cultured atrial cardiocytes

We have developed a novel system to study stretch-dependent secretion of atrial natriuretic peptide (ANP) using cultured neonatal rat atriocytes in vitro. Application of tension (i.e., 2 sequential stretches) to cells grown on a flexible culture surface effected a dose-dependent increase in immunoreactive (ir) ANP release into the medium. Analysis of atriocyte cytoplasmic RNA 24 h poststretch revealed an increase in ANP mRNA levels of about ninefold relative to the unstretched controls. Medium ATP levels, measured as an index of cellular damage, were similar in control and stretched cells. Furthermore, cooling the cultures to 0 degrees C suppressed both basal as well as stretch-stimulated release. These findings argue against cellular damage and nonspecific release of irANP as an explanation for the increase in medium immunoreactivity. Stretch was incapable of amplifying the secretory response to prostaglandin F2 alpha, suggesting possible overlap in the pathways whereby these stimuli effect release of the peptide. The calcium channel blocker verapamil had no effect on stretch-dependent irANP release, whereas calmidzolium, a calmodulin inhibitor, suppressed basal as well as stretch-dependent secretion, implying a potentially important relationship between intracellular calcium metabolism and irANP release.