The renal (kNBC1) and intestinal (pNBC1) Na+ /HCO3- cotransporter subtypes differ in their structure, transport direction, and response to secretagogues. Previous studies have suggested that cAMP-dependent regulation of pNBC1 is not only influenced by its unique N-terminus, but also by the cell type in which it is expressed. After having shown activation of NBC by carbachol in murine colon, we now investigated this pathway in renal HEK293 cells transiently expressing a GFP-tagged pNBC1 construct. Na+ - and HCO3--dependent pHi recovery from an acid load (measured with BCECF) was accelerated by factor 5 in GFP-positive cells compared to the control in the presence of CO2/HCO3-, and similar in its absence. Forskolin (10-5 M) had no effect in non- transfected cells, but inhibited pHi recovery in cells expressing pNBC1 by 62%. After carbachol (10-4 M) preincubation, pHi recovery occurred somewhat faster in non-transfected cells, indicating activation of endogenous NBC which was also detected by PCR. However, no additional effect was noticed in the presence of GFP-pNBC1. Acid-activated Na+ /HCO3- cotransport via pNBC1 expressed in renal cells is thus inhibited by cAMP and not affected by cholinergic stimulation, which is in contrast to the findings in native intestinal tissue. We conclude that not only cAMP-dependent, but also cholinergic regulation of pNBC1 occurs in a cell-type specific manner.