EFFECT OF SECRETIN AND INHIBITORS OF HCO3- H+ TRANSPORT ON THE MEMBRANE VOLTAGE OF RAT PANCREATIC DUCT CELLS/

The aim of the present study was to study the effect of secretin on th e electrophysiological response of pancreatic ducts. Furthermore, we i nvestigated the effects of lipid-soluble buffers and inhibitors of HCO 3-/H+ transport. Ducts obtained from fresh rat pancreas were perfused in vitro. Secretin depolarized the basolateral membrane voltage, V-bl, by up to 35 mV (n = 37);a half-maximal response was obtained at 3 X 1 0(-11) mol/l. In unstimulated ducts a decrease in the luminal Cl- conc entration (120 to 37 mmol/l) had a marginal effect on V-bl, but after maximal secretin stimulation it evoked a 14 +/- 2 mV depolarization (n = 6), showing that a luminal Cl- conductance (G(cl-)) was activated. The depolarizing effect of secretin on V-bl was often preceded by abou t a 6 mV hyperpolarization, most likely due to an increase in the baso lateral G(K-). Perfusion of ducts with DIDS (4,4'-diisothiocyanatostil bene-2,2'-disulphonic acid, 0.01 mmol/l) or addition of ethoxzolamide (0.1 mmol/l) to the bath medium diminished the effect of secretin. Ace tate or pre-treatment of ducts with NH4+/NH3 (10 mmol/l in the bath) d epolarized the resting V-bl of -65 +/- 2 mV by 16 +/- 4 mV (n = 7) and 19 +/- 3 mV (n = 10), respectively. The fractional resistance of the basolateral membrane (FR(bl)) doubled, and the depolarizing responses to changes in bath K+ concentrations (5 to 20 mmol/l) decreased from 2 2 +/- 1 to 11 +/- 2 mV. The Na+/H+ antiporter blocker EIPA (5-[N-ethyl -N-isopropyl]-amiloride, O.1 mmol/l) also depolarized V-bl by 10 +/- 1 mV, FR(bl) increased and the response to K+ concentration changes dec reased (n = 7). Effects of EIPA and ethoxzolamide on V-bl were greater in ducts deprived of exogenous HCO3-/CO2. Taken together, the present study shows that secretin increased the basolateral G(K+) and the lum inal G(Cl-). The depolarizing effect of secretin was diminished follow ing inhibition of HCO3- transport (DIDS), or HCO3-/H+ generation (etho xzolamide). Manoeuvres that presumably led to lowered intracellular pH (NH4+/NH3 removal, acetate, EIPA) decreased the basolateral G(K+). Th e present data support our previously published model for pancreatic H CO3- secretion, and indicate that the basolateral membrane possesses a pH-sensitive G(K+).