INTRACELLULAR ALKALINIZATION STIMULATES BILE-FLOW AND VESICULAR-MEDIATED EXOCYTOSIS IN IPRL

Intracellular PH recovery from an acute alkaline load in rat hepatocyt es is mediated by a Cl--HCO3- exchanger, which is electroneutral, Naindependent, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DID S) sensitive. Stimulation of this Cl--HCO3- exchanger requires intact microtubules, suggesting that vesicular transport may be required to a ctivate this exchanger. To determine if intracellular alkalinization s timulates biliary HCO3- excretion and bile flow in the intact liver by vesicle-mediated exocytosis, isolated perfused rat livers (IPRL) were alkalinized by two protocols. Isohydric changes in CO2 and HCO3- conc entrations induced transient increases in bile flow by 36% (P < 0.01), which were abolished by DIDS (0.01 mM), inhibited by pretreatment wit h colchicine (P = 0.01), but not affected by membrane depolarization w ith the K+-channel blocker BaCl2 (1 mM). Similarly, perfusion with 20 mM NH4Cl produced a 42% increase in bile flow (P < 0.01) and a 26% inc rease in biliary HCO3- excretion. Both the increases in bile flow and HCO3- excretion were almost completely blocked by DIDS and inhibited b y pretreatment with colchicine (P < 0.01). Biliary excretion of horser adish peroxidase was also increased during intracellular alkalinizatio n with either protocol (P < 0.01). These findings suggest that intrace llular alkalinization stimulates bile flow and biliary HCO3- excretion . Microtubule-dependent vesicular-mediated exocytosis is involved in t his response.