Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

October 1992

Abstract

A stable intracellular ionic environment is necessary for hepatocytes to function normally. Thus, during hypotonic shock or L-alanine uptake, hepatocytes swell and then exhibit a regulatory volume decrease (RVD), which comprises an increase in K$\sp+$ conductance (G$\sb{\rm K}$), an increased K$\sp+$ efflux, and a hyperpolarization of transmembrane potential (V$\sb{\rm m}$). Since hepatocyte intracellular Cl$\sp-$ has been demonstrated to distribute passively with V$\sb{\rm m}$, this study is designed to test the hypothesis that the hypotonic shock- or L-alanine uptake-induced hyperpolarization of V$\sb{\rm m}$ might provide an electromotive force for the efflux of hepatocyte intracellular Cl$\sp-$, which in turn would contribute osmotically to the RVD in hepatocytes. Double-barreled ion-selective microelectrodes were used to measure the changes of hepatocyte transmembrane potential, intracellular ionic activities (especially intracellular Cl$\sp-$ activity, (a$\sp{\rm i}\sb{\rm Cl}$)), and intracellular water volume during either anisotonic stress or L-alanine uptake. Hepatocyte V$\sb{\rm m}$ hyperpolarized, (a$\sp{\rm i}\sb{\rm Cl}$) decreased, intracellular K$\sp+$ activity (a$\sp{\rm i}\sb{\rm K}$) decreased, and intracellular water volume increased during hyposmotic stress. When perfused with L-alanine, hepatocyte V$\sb{\rm m}$ exhibited a transient depolarization followed by repolarization and then underwent a constant hyperpolarization. Meanwhile, hepatocyte intracellular Na$\sp+$ activity (a$\sp{\rm i}\sb{\rm Na}$) increased, a$\sp{\rm i}\sb{\rm K}$ & a$\sp{\rm i}\sb{\rm Cl}$ decreased, and intracellular water volume increased. In both hypotonic shock and L-alanine uptake conditions, the decreased a$\sp{\rm i}\sb{\rm K}$ could be attributed to cell swelling. However, the decrease in a$\sp{\rm i}\sb{\rm Cl}$ was greater than could be accounted for by cell swelling. When the change of V$\sb{\rm m}$ was inhibited by K$\sp+$ channel blockers, the change of a$\sp{\rm i}\sb{\rm Cl}$ was also inhibited. Based on the measured a$\sp{\rm i}\sb{\rm Cl}$, Cl$\sp-$ was always at its electrochemical equilibrium in all of the control and experimental conditions. The conclusions of this study emphasize the passive distribution of hepatocyte intracellular Cl$\sp-$ with the changes of V$\sb{\rm m}$ induced by hypotonic stress and L-alanine uptake. Thus, the data strongly support the idea that the hypotonic shock- or L-alanine uptake-induced hyperpolarization of V$\sb{\rm m}$ provides electromotive force for the efflux of hepatocyte intracellular Cl$\sp-$. This could contribute to hepatocyte volume regulation during both hypotonic shock and organic solute transport.

Document Type

Dissertation - unrestricted

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