Difference in effect of atrial natriuretic peptide on cGMP in aortic and coronary smooth muscle cells

Blood vessels show a heterogeneous response to the atrial natriuretic peptide (ANP). In our experiments thoracic aorta from the guinea pig relaxed in response to atriopeptin III (AP; rat ANP-103-126) and to sodium nitroprusside (SNP). In contrast, in perfused guinea pig hearts, AP III produced no change in coronary flow, while SNP increased flow. In smooth muscle cells cultured from the coronary system (CASM) and from the thoracic aorta (TASM), we compared receptor binding and the effects on guanosine 3',5'-cyclic monophosphate (cGMP) production of AP III. AP III bound specifically with equal affinity and with equivalent numbers of binding sites in both cell types. AP III produced a dose-dependent increase in cGMP in TASM (50% effective concentration approximately 3 nM) with a maximum 11-fold increase over basal at 1 microM AP III. In contrast, in CASM, AP III failed to increase cGMP. Nitroprusside increased cGMP in both cell types. Autoradiograms of 125I-labeled AP III linked to cell membranes showed bands at 70 kDa (ANP-C receptor) in both cell types. A second band at 140 kDa (ANP-B receptor) was only seen in TASM. These results suggest that smooth muscle cells of coronary resistance vessels of the guinea pig do not express the particulate guanylyl cyclase that is activated by ANP.