A role for a pertussis toxin-sensitive trimeric G-protein in store-operated Ca²⁺ inflow in hepatocytes

The mechanism of store-operated Ca²⁺ inflow in hepatocytes was investigated using fluo-3 and fura-2 to monitor changes in the concentration of intracellular free Ca²⁺ in single cells, and 1-(α-glycerophosphoryl)-myo-inositol 4,5-diphosphate, P⁴⁽⁵⁾-1-(2-nitrophenyl)ethyl ester ('caged' GPIP₂) and 'caged' guanosine 5′-[γthio]triphosphate (GTPγS) (introduced into the cytoplasmic space by microinjection), thapsigargin and 2,5-di-tert-butylhydroquinone (DBHQ) to stimulate Ca²⁺ inflow. Photolysis of 'caged' GPIP₂ or 'caged' GTPγS stimulated Ca²⁺ inflow. The abilities of GPIP₂, thapsigargin and DBHQ to stimulate Ca²⁺ inflow were inhibited by the pre-treatment of hepatocytes with pertussis toxin in vivo for 36 h. Thapsigargin-stimulated Ca²⁺ inflow was also inhibited by guanosine 5′-[β-thio]diphosphate (GDPβS) (introduced by microinjection). It is concluded that, in hepatocytes, store-operated Ca²⁺ inflow induced by the actions of either inositol 1,4,5-trisphosphate, thapsigargin or DBHQ requires a pertussis toxin-sensitive trimeric G-protein.