Effects of bile acids on cystolic Ca++ activity and cell viability of isolated rat hepatocytes were studied to test the hypothesis that bile acids may produce hepatotoxicity by increasing cystolic Ca++ activity. Changes in cystolic Ca++ activity were calculated from time-dependent changes in fluorescence of quin-2 loaded hepatocytes. Release of lactate dehydrogenase and changes in propodium iodide fluorescence were used to assess cell viability. Bile acids studied were unconjugated and taurine-conjugated cholate, chenodeoxycholate (and taurochenodeoxycholate), deoxycholate (and taurodeoxycholate) and lithocholate (and taurolithocholate). With the exception of cholate and taurocholate, bile acids increased cystolic Ca++ activity within 10 to 30 sec in a concentration-dependent fashion (0.05 to 1.0 mM) and in the order lithocholate = taurolithocholate greater than chenodeoxycholate = taurochenodeoxycholate = deoxycholate = taurodeoxycholate. The initial increase in cystolic Ca++ activity by bile acids was not due to cell damage, since bile acid-induced decreases in cell viability were not significant until 2 to 3 min. At higher concentrations of unconjugated bile acid, there was a secondary increase in quin-2 fluorescence corresponding temporally to the increase in propodium iodide fluorescence, indicating cell damage after the initial increase in cystolic Ca++ activity. The ability of conjugated and unconjugated bile acids to increase cystolic Ca++ activity was abolished and decreased (60 to 90%), respectively, in the absence of extracellular Ca++, indicating that extracellular Ca++ is the major source of the bile acid-induced increase in cystolic Ca++ activity.(ABSTRACT TRUNCATED AT 250 WORDS)