Micropuncture analysis of the cellular mechanisms of electrolyte secretion by the in vitro rabbit pancreas

Micropuncture techniques have been used to study electrolyte secretion by the spontaneously secreting in vitro rabbit pancreas over a wide range of environmental conditions. Pancreatic secretion does not have a strong requirement for HCO3 and secretion continues at nearly normal rates when exogenous HCO3 is replaced by acetate. Acetate concentration in the juice averages 70 meq/liter, nearly three times the environmental concentration. The similar characteristics exhibited by HCO3 and acetate secretion indicate that they are secreted by a common mechanism involving active H transport. In vitro acid-base alterations demonstrate that the secretion rate is controlled by the environmental HCO3 concentration and to a much lesser extent by the pCO2. Secretion also requires active Na transport across the mucosal membrane. The effects of ouabain and a low Na environment strongly suggest coupling between the transport of Na and H and a cellular mechanism for electrolyte secretion is proposed involving Na-H exchange mechanisms at both the mucosal and serosal membranes.