Atrial Natriuretic Factors Stimulate Accumulation and Efflux of Cyclic GMP in C6–2B Rat Glioma and PC12 Rat Pheochromocytoma Cell Cultures

Abstract

Atrial natriuretic factors (ANFs) were tested for their effects on cyclic GMP production in two neurally derived cell lines, the C6–2B rat glioma cells and the PC12 rat pheochromocytoma cells. These cell lines were selected because both are known to possess high amounts of the particulate form of guanylate cyclase, a proposed target of ANF in peripheral organs. Previous studies from our laboratory have shown that ANF selectively activates paniculate, but not soluble, guanylate cyclase in homogenates of a variety of rat tissues and that one class of ANF receptor appears to be the same glycoprotein as particulate guanylate cyclase. In the present study we found that four analogs of ANF stimulate cyclic GMP accumulation in both C6–2B and PC12 cells with the rank order of potency being atriopeptin HI = atriopeptin II ≥ human atrial natriuretic polypeptide ≥ atriopeptin I. Atriopeptin II (100 nM) for 20 min elevated cyclic GMP content in C6–2B cells fourfold and in PC12 cells 12‐fold. Atriopeptin II (100 nM) for 20 min also stimulated the efflux of cyclic GMP from both C6–2B cells (47‐fold) and PC12 cells (12‐fold). Accumulation of cyclic GMP in both cells and media was enhanced by preincubation with the phosphodiesterase inhibitor 3‐isobutyl‐1‐methylxanthine (250 μM). After 20 min of exposure to atriopeptin II, cyclic GMP amounts in the media were equal to or greater than the amounts in the cells. Although the function of cyclic GMP in neural tissue is at present unclear, the cyclic GMP response observed in C6–2B and PC12 cells may provide important clues concerning the molecular mechanisms of action of ANF in the central and peripheral nervous systems. Since a significant amount of the generated cyclic GMP is released from these cells in response to ANF, extracellular as well as intracellular cyclic GMP may be important in mediating the actions of ANF in neural tissues.