AJP - Gastrointestinal and Liver Physiology, Vol 269, Issue 1 73-G84, Copyright © 1995 by American Physiological Society

ARTICLES

Microscope laser light-scattering spectroscopy of vesicles within canaliculi of rat hepatocyte couplets

G. M. Mockel, S. Gorti, R. K. Tandon, T. Tanaka and M. C. Carey
Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, USA.

Employing microscope laser light-scattering spectroscopy, we investigated "primary" bile secretion into canalicular spaces of rat hepatocyte couplets in monolayer culture. Time-dependent scattered light intensities were fitted by bi-exponential decays. The "slow" decay was attributed to an undulating canalicular membrane motion, whereas the "fast" decay was consistent with rapidly diffusing intracanalicular vesicles with mean hydrodynamic radii (+/- SD) of 479 +/- 53 A. After addition of micromolar concentrations of common bile salts, increases in the amplitude of the fast component facilitated a quantitative estimate of vesicle secretion rates. A dose-response relationship with 0.1-200 microM sodium taurocholate was characterized by an initial concentration-dependent increase and then a decrease in the amplitude of the fast canalicular component. Since these taurocholate concentrations are nontoxic to cultured hepatocytes, the maximum in vesicle-sized particles at 10 microM taurocholate suggested that its critical micellar concentration of approximately 5 mM was attained within the canalicular spaces. Sodium taurolithocholate resulted in time- and dose-dependent diminution in vesicle secretion rates, which after 2 h was followed by spontaneous canalicular recovery. This suggested that acute bicellular "cholestasis" was followed by oxidative metabolism and detoxification of the monohydroxy bile salt. Microscope laser light-scattering spectroscopy should facilitate further physical-chemical and pathophysiological studies of bile secretion at the cellular level.

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