Phospholipase C signaling tonically represses basal atrial natriuretic factor secretion from the atria of the heart

Abstract

The cardiac hormone atrial natriuretic factor (ANF or ANP) plays significant, well-established roles in a large number of physiological and pathophysiological processes, including water and electrolyte balance, blood pressure regulation, and cardiovascular growth. Understanding the regulation of its production and secretion by atrial cardiomyocytes is incomplete. We have previously established a significant role of Gi/o protein signaling in modulating ANF secretion as promoted by stretch of the atrial myocardium. In the present study, we investigated the role of Gq protein signaling and its relationship to Gi/o protein signaling using pharmacological manipulation of proximal effectors of Gαq in an ex vivo model of spontaneously beating rat atria. Phospholipase C (PLC) and protein kinase C (PKC) inhibitors dramatically increased basal secretion of ANF. Furthermore, although atrial wall stretch is a potent stimulus for secretion, stretch unexpectedly reduced ANF secretion to basal levels under PLC and PKC inhibitory conditions. Inhibition of the inositol triphosphate receptor did not appear to affect basal secretion but dose-dependently blocked stretch-secretion coupling. The results obtained demonstrate that the PLC and PKC signaling cascades play important albeit unexpected roles in the regulation of basal and stimulated ANF secretion and suggest interplay between the Gq and Gi/o protein signaling pathways.