Hepatic sinusoidal endothelial fenestrae express plasma membrane Ca(++)pump and Ca++Mg++-ATPase

Background/Aim: In general, intracytoplasmic free calcium ions (Ca++) are m aintained at a very low concentration in mammalian tissue by extruding Ca+ against a high concentration of extracellular Ca++, mainly through the act ivity of the plasma membrane Ca(++)pump-ATPase. The aim of the present stud y was to demonstrate by electron cytochemical and immunogold methods the ul trastructural localization of two different types of plasma membrane Ca++-A TPase, i.e. Ca++Mg++-ATPase and Ca++ pump-ATPase in the hepatic sinusoidal endothelium. Methods: Liver tissues and the isolated hepatic sinusoidal end othelial cell (SEC)s were subjected to the following procedures. The ultras tructural localizations of Ca++Mg++-ATPase were examined by an electron cyt ochemical method. The ultrastructural localization of Ca(++)pump-ATPase was identified by an electron immunogold method. Results: The cytochemical rea ction of Ca++Mg++-ATPase was found to be localized on the outer sites of th e plasma membrane of sinusoidal endothelial fenestrae (SEF). The immunogold particles indicating the presence of Ca pump-ATPase were identified on the inner sites (cytoplasmic) of the invaginated plasma membrane of SEE Conclu sions: Both Ca++Mg++-ATPase and Ca(++)pump-ATPase demonstrated on the SEF p lasma membrane may be involved in the regulation of intracytoplasmic Ca++ c oncentration.