MICROSCOPE LASER LIGHT-SCATTERING SPECTROSCOPY OF VESICLES WITHIN CANALICULI OF RAT HEPATOCYTE COUPLETS

Employ ing microscope laser light-scattering spectroscopy, we investig ated ''primary'' bile secretion into canalicular spaces of rat hepatoc yte couplets in monolayer culture. Time-dependent scattered light inte nsities were fitted by bi-exponential decays. The ''slow'' decay was a ttributed to an undulating canalicular membrane motion, whereas the '' fast'' decay was consistent with rapidly diffusing intracanalicular ve sicles with mean hydrodynamic radii (+/-SD) of 479 +/- 53 Angstrom. Af ter addition of micromolar concentrations of common bile salts, increa ses in the amplitude of the fast component facilitated a quantitative estimate of vesicle secretion rates. A dose-response relationship with 0.1-200 mu M sodium taurocholate was characterized by an initial conc entration-dependent increase and then a decrease in the amplitude of t he fast canalicular component. Since these taurocholate concentrations are nontoxic to cultured hepatocytes, the maximum in vesicle-sized pa rticles at 10 mu M taurocholate suggested that its critical micellar c oncentration of similar to 5 mM was attained within the canalicular sp aces. Sodium taurolithocholate resulted in time- and dose-dependent di minution in vesicle secretion rates, which after 2 h was followed by s pontaneous canalicular recovery. This suggested that acute bicellular ''cholestasis'' was followed by oxidative metabolism and detoxificatio n of the monohydroxy bile salt. Microscope laser light-scattering spec troscopy should facilitate further physical-chemical and pathophysiolo gical studies of bile secretion at the cellular level.