Ca2+ depletion and inositol 1,4,5-trisphosphate-evoked activation of Ca2+ entry in single guinea pig hepatocytes

Store-operated Ca2+ entry was investigated by monitoring the Ca2+-dependent K+ permeability in voltage-clamped guinea pig hepatocytes, In physiologica l conditions, intracellular Ca2+ stores are discharged following agonist st imulation, but depletion of this stores can be achieved using Ca2+-Mg2+-ATP ase inhibitors such as 2,5-di(tert-butyl)-1,4-benzohydroquinone and thapsig argin. The effect of internal Ca2+ store depletion on Ca2+ influx was teste d in single cells using inositol 1,4,5-trisphosphate (InsP(3)) release from caged InsP(3) after treatment of the cells with 2,5-di(tert-butyl)-1,4-ben zohydroquinone or thapsigargin in Ca2+-free solutions. We show that the pho tolytic release of 1-D-myo-inositol 1,4-bisphosphate 5-phosphorothioate, a stable analog of InsP(3), and Ca2+ store depletion have additive effects to activate a high level of Ca2+ entry in single guinea pig hepatocytes, Thes e results suggest that there is a direct functional interaction between Ins P(3) receptors and Ca2+ channels in the plasma membrane, although the natur e of these Ca2+ channels in hepatocytes is unclear.