Internal perfusion of guinea‐pig hepatocytes with buffered Ca2+ or inositol 1,4,5‐trisphosphate mimics noradrenaline activation of K+ and Cl− conductances

Abstract

External application of noradrenaline to voltage-clamped guinea-pig isolated hepatocytes evoked membrane conductance increases to K⁺ and Cl⁻. This effect was reproduced by internal perfusion of the cells with 2 μM buffered Ca²⁺ and with 20 μM inositol 1,4,5-trisphosphate (IP₃). The kinetic properties of the K⁺ conductance and its selective block by the toxin apamin were the same in each case. Cyclical fluctuations of conductance observed with noradrenaline were reproduced by internal IP₃ but not by Ca²⁺ perfusion, indicating that oscillations of intracellular free Ca²⁺ may arise from properties of the Ca²⁺ sequestration mechanism at constant IP₃ concentration.