Premium
Extracellular ATP, intracellular calcium and canalicular contraction in rat hepatocyte doublets
Author(s) -
Kitamura Tsuneo,
Brauneis Ulrike,
Gatmaitan Zenaida,
Arias Irwin M.
Publication year - 1991
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.1840140411
Subject(s) - extracellular , myosin light chain kinase , biophysics , hepatocyte , contraction (grammar) , myosin , chemistry , biochemistry , actin , calcium , intracellular , egta , biology , endocrinology , organic chemistry , in vitro
Bile‐canaliculus contraction in rat hepatocyte doublets is postulated to involve activation of an actinmyosin system. We examined this hypothesis by determining the relationship between canalicular contraction and cystolic free Ca 2+ ([Ca 2+ ] i ) concentration after extracellular addition of ATP or microdialysis of myosin light chain kinase or its Ca 2+ ‐independent fragment, which retains catalytic activity. After incubation of doublets with 200 μmol/L ATP in the absence of extracellular Ca 2+ , [Ca 2+ ] i peaked at 40 sec and 71% of canaliculi contracted within 4 min. Decreasing effects were observed with equimolar ADP, AMP and nonhydrolyzable ATP, but no effect was observed with adenosine. The effect of extracellular ATP on [Ca 2+ ] i and canalicular contraction was dose dependent. Addition of extracellular Ca 2+ and ATP resulted in a plateau level of [Ca 2+ ] i . Cytochalasin D, which depolymerizes actin filaments, inhibited ATP‐induced canalicular contraction, but not the increase in [Ca 2+ Microdialysis of myosin light chain kinase and its Ca 2+ ‐independent fragment (but not the heatdenatured fragment, albumin, trypsin plus soybean inhibitor or buffer) into one hepatocyte of a doublet resulted in canalicular contraction in 86% of doublets. Injection of myosin light chain kinase or its Ca 2+ ‐independent fragment did not increase [Ca 2+ ] i within 5 min. These results indicate that (a) the basolateral plasma membrane of hepatocytes has a P 2Y ‐class purinoceptor, (b) increased [Ca 2+ ] i after incubation with ATP is initially due to mobilization from internal sites and (c) canalicular contraction is directly related to [Ca 2+ ] i and activation of an actin‐myosin system. The physiological role of extracellular ATP in canalicular contraction is uncertain. (H EPATOLOGY 1991;14:640–647.)