Evidence for norepinephrine-activated Ca²⁺ permeable channels in guinea-pig hepatocytes using a patch clamp technique

抄録

To determine whether the hepatocyte plasma membrane possesses a Ca²⁺ channel, we applied a patch clamp technique to isolated guinea-pig hepatocytes. In a cell-attached configuration, using an internal pipette solution of 110 mM BaCl₂ or CaCl₂, we observed sporadic inward single channel currents (Po=0.004±0.002, n=6) at various membrane potentials. The unit amplitude was 0.60±0.15 pA (n=6) at resting membrane potential. The single channel conductance was 20.4±4.6 pS (n=6) and this channel showed no rectification and no voltage dependence. Bay K 8644, a dihydropyridine Ca²⁺ channel activator, did not affect this channel activity. Although norepinephrine in the pipette solution did not activate this channel, its external application increased channel activity. These observations suggest that guinea-pig hepatocytes possess Ca²⁺ permeable channels that differ from the voltage-operated Ca²⁺ channels found in excitable cells and that such channels are responsible for the agonist-stimulated Ca²⁺ entry in hepatocytes. (J Nippon Med Sch 1999 ; 66 : 127-133)