EVIDENCE FOR APICAL NA+ H+ EXCHANGER IN BOVINE MAIN PANCREATIC DUCT/

The finding of a high PCO2 in basally secreted pancreatic juice of man and dog raises the hypothesis of proton secretion from ductal epithel ial cells presumably through a Na+/H+ exchanger. To test this possibil ity, H+ luminal secretion and Na+ movements were measured in vitro on samples of bovine pancreatic ducts mounted in Ussing-type chambers. Th e rate of luminal acidification measured by the pH stat method, using bicarbonate-free media gassed with 100% O-2, reached 2.75 mu Eq/cm(2)/ hr. Proton secretion was blocked in the presence of 1 mM amiloride or in the absence of Na+ (replaced by choline) in the mucosal solution. S tudy of transepithelial Na-22 fluxes in short-circuited tissue, bathed on both sides by control Ringer solution, gassed by 95% O-2-5%; CO2 d emonstrated a net sodium transport from the mucosal to the interstitia l side of the duct (net Na-22 flux = 3.23 +/- 0.8 mu Eq/cm(2)/hr). Thi s net sodium transport was electroneutral and blocked by mucosal amilo ride (0.5-1 mM/liter) or by interstitial ouabain (1 mM/liter). These r esults are consistent with the existence of a Na+/H+ exchanger on the luminal side of the bovine main pancreatic duct.