Ca2+-dependent K+channels in neuroblastoma hybrid cells activated by intracellular inositol trisphosphate and extracellular bradykinin

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Abstract
Bradykinin (BK) activation of phosphatidylinositide breakdown in NG108‐15 neuroblastoma x glioma hybrid cells in the generation of an outward K+ current through the release of Ca2+ by the intermediary messenger inositol 1,4,5‐trisphosphate (InsP3). Channels mediating this outward current were identified using cell‐attached patch electrodes. Intracellular iontophoretic injection of InsP3 or Ca2+, or extracellular application of BK, evoked bursts of K+ channel activity coincident with cell hyperpolarization measured with an intracellular recording micropipette. The most frequent channels had a mean single‐channel conductance of about 40 pS in symmetrical K+ solutions; additional openings of lower conductance (18 pS) channels were also detected. Bath application of phorbol dibutyrate (PDBu, 1 μM) increased the number and opening probability of the InsP3‐induced channels.