Regulation of anion secretion by nitric oxide in human airway epithelial cells

Nitric oxide (NO) is continuously produced and released in human airways, but the biological significance of this process is unknown. In this study, we have used Calu-3 cells to investigate the effects of NO on transepithelial anion secretion. An inhibitor of NO synthase, N-G-nitro-L-arginine methyl ester, reduced short-circuit current (Isc), whereas an NO donor, S-nitrosoglutathione (GSNO), increased I-sc, with an EC50 similar to1.2 muM. The NO-activated current was inhibited by diphenylamine-2-carboxylate, clotrimazole, and charybdotoxin. Selective permeabilization of cell membranes indicated that NO activated both apical anion channels and basolateral potassium channels. An inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-alpha ]quinoxalin-1-one, prevented activation of I-sc by NO but not by 8-bromo-cGMP, suggesting that NO acts via a cGMP-dependent pathway. Sequential treatment of cells with forskolin and GSNO or 1-ethyl-2-benzimidazolinone and GSNO showed additive effects of these chemicals on I-sc. Interestingly, GSNO elevated intracellular Ca2+ concentration ([Ca2+](i)) but had no effect on I-sc activated by thapsigargin. These results show that NO activates transepithelial anion secretion via a cGMP-dependent pathway that involves cross talk between NO and [Ca2+](i).