Endothelin and nitric oxide (NO) modulate ion transport in the kidney. In this study we defined the function of ET receptor subtypes and the NO-guanylate cyclase signaling pathway in mediating the adaptation of the cortical collecting duct (CCD) to metabolic acidosis. CCDs were perfused in vitro and incubated for 3 h at pH 6.8, and bicarbonate transport or cell pH measured before and after acid incubation. Luminal chloride was reversibly removed to isolate H⁺ and HCO₃^- secretory fluxes, and to raise the pH of -intercalated cells. Acid incubation caused reversal of polarity of net HCO₃^- transport from secretion to absorption, comprised of a 40% increase in H⁺ secretion and a 75% decrease in HCO₃^- secretion. The ET_B receptor antagonist BQ788, as well as the NO synthase inhibitor, L-NAME, attenuated by 40% the adaptive decrease in HCO₃^- secretion, but only BQ788 inhibited the adaptive increase in H⁺ secretion. There was no effect of inactive D-NAME or the ET_A receptor antagonist BQ123. Both BQ788 and L-NAME inhibited the acid-induced inactivation (endocytosis) of apical Cl^-/HCO₃^- exchanger. The guanylate cyclase inhibitor LY83583 and cyclic GMP-dependent protein kinase inhibitor KT5823 affected HCO₃^- transport similarly to L-NAME. These data indicate that signaling via the ET_B receptor regulates the adaptation of the CCD to metabolic acidosis, and that the NO-guanylate cyclase component of ET_B receptor signaling mediates down-regulation of Cl^-/HCO₃^- exchange and HCO₃^- secretion.