NITRIC-OXIDE PRODUCTION REGULATES CGMP FORMATION AND CALCIUM INFLUX IN PANCREATIC ACINAR-CELLS

Nitric oxide production regulates cGMP formation and calcium influx in pancreatic acinar cells. Am. J. Physiol. 266 (Gastrointest. Liver Physiol. 29): G350-G356, 1994. - Guanosine 3',5'-cyclic monophosphate (cGMP) rise is one of the early events in neurotransmitter or hormone-induced cascade of reactions in pancreatic acinar cells. The mechanism of agonist-stimulated guanylyl cyclase activation in these cells remains, however, unknown. In the present work, mechanisms of cGMP rise, as well as of Ca2+ influx, induced by carbachol were studied on acinar cells isolated from rat and guinea pig pancreas. In both types of acinar cells, blocking nitric oxide (NO) production by inhibitors of NO synthase, N-G-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arginine, abolished carbachol-induced cGMP rise in a dose-dependent manner. The inhibition was reversed by addition of excess L-arginine. L-NMMA also caused inhibition of the basal cGMP level, suggesting a role for NO in cGMP homeostasis in resting cells. Carbachol was found to increase [H-3]arginine conversion to [H-3]citrulline. This conversion was inhibited by L-NMMA. By contrast, inhibition of carbon monoxide production by Zn-protoporphyrin did not affect carbachol-stimulated cellular cGMP levels. There was no increase in cellular cGMP levels in response to exogenous arachidonic acid (AA). Blocking of lipoxygenase oxidation of AA by nordihydroguaiaretic acid did not produce any changes in carbachol-induced cGMP rise. Indomethacin, a cyclooxygenase inhibitor, increased basal cGMP level through L-NMMA-sensitive mechanism. Blockade of NO production inhibited carbachol-induced increase in Ca-45(2+) uptake in both guinea pig and rat acinar cells. The concentration-response curves for inhibition by L-NMMA of Ca-45(2+) uptake and cGMP formation were superimposable. L-NMMA also suppressed stimulation of Mn2+ quenching by carbachol in fura 2-loaded acini. In conclusion, these findings indicate the involvement of NO in regulation of cGMP and Ca2+ transport in pancreatic acinar cells.