IP(3)-ACTIVATED CALCIUM-PERMEABLE CHANNELS IN THE INSIDE-OUT PATCHES OF CULTURED CEREBELLAR PURKINJE-CELLS

Inositol-1,4,5,-trisphosphate (IP3)-activated calcium-permeable channels were recorded from inside-out patches of cultured cerebellar Purkinje cells. When 2-5 muM of IP3 was applied to the internal surface of the inside-out patches, inward Ba2+ currents were activated within 10 sec following the application in 11 out of 24 patches. In the presence of heparin (100 mug/ml), activation of Ba2+ currents by IP3 was inhibited. Unitary currents with different amplitudes and kinetics were observed; small and large unitary currents, and rapid fluctuations with various amplitudes. The small unitary currents (single channel conductance; 5.6 pS) were most frequent. Addition of inositol 1,3,4-trisphosphate (2-5 muM) slightly activated Ba2+ currents in 2 out of 10 patches, but the amount of the increment was much smaller than that produced by IP3. These results suggest a possibility that IP3 directly activates Ca2+-permeable channels in the plasma membrane of cerebellar Purkinje cells.