Decrease in the Number of Ca2+ Channel in Liver Membranes from Bile Duct Ligated Rat

• Published in: Japanese Journal of Pharmacology 1997, Vol.73 (suppl.1), p.188-188
• Main Authors: Tsuji, Mayumi, Yamazaki, Yukako, Okazaki, Masako, Yoshida, Yasuko, Oguchi, Katsuji
• Format: Article
• Language: English
• ISSN: 0021-5198; 1347-3506
• DOI: 10.1016/S0021-5198(19)45253-0

We previously reported that the cholestatic cultured hepatocytes were imparied vesicle exocytosis depending on cytosolic free Ca^2+ ([Ca^2+ ] i). The aim of this study is to determine if this impairment of vesicle exocytosis in cholestatic hepatocytes may be related to damage of calcium channel or decrease in the number of Ca^2+ channel. Male Sprague-Dawley rats were used after common bile duct ligation for 1 or 2 days. Serum total bilirubin (T-bil) and total cholesterol (TC) as cholestasis marker for bile duct ligated rat were determined. As [^^3 H] -nitrendipine binding assay, enriched membranes fraction from the rat liver was incubated for 40 min at 10℃ in 50 mM Tris-HCl buffer at pH7.5 with the required concentration of [^^3 H] -nitrendipine. Non-specific binding was measured in the presence of BAY K 8644 (Ca^2+ channel agonist). T-bil and TC in serum after bile duct ligation were significantly increased compared to those from normal rat. In normal membrane fraction, the apparent equilibrium dissociation constant (K_D ) was 9.70±1.08 nM and the maximum density of binding (Bmax) was 1.15±0.35 pmol/mg of protein determined from Scatchard analysis of binding. However, in cholestasis, the Bmax was significantly decreased and K_D was slightly increased. The Bmax values were negatively correlated with T-bil and TC concentrations in serum (r=0.63, 0.69, respectively). These results indicate that the decrease in the number of Ca^2+ channel on liver plasma membranes partly induces the impairment of vesicle exocytosis depending on [Ca^2+ ]i.