Inhibition of acetylcholine-activated K+ currents by U73122 is mediated by the inhibition of PIP2-channel interaction

摘要

class="enumerated" style="list-style-type:decimal">We have investigated the effect of , a specific inhibitor of phospholipase C (PLC), on acetylcholine-activated K⁺ currents (IKACh) in mouse atrial myocytes.In perforated patch clamp mode, IKACh was activated by 10 μM acetylcholine. When atrial myocytes were pretreated with or , IKACh was inhibited dose-dependently (half-maximal inhibition at 0.12±0.0085 and 0.16±0.0176 μM, respectively). The current-voltage relationships for IKACh in the absence and in the presence of showed that the inhibition occurred uniformly from −120 to +40 mV, indicating a voltage-independent inhibition.When was applied after IKACh reached steady-state, a gradual decrease in IKACh was observed. The time course of the current decrease was well fitted to a single exponential, and the rate constant was proportional to the concentration of .When KACh channels were directly activated by adding 1 mM GTPγS to the bath solution in inside-out patches, (1 μM) decreased the open probability significantly without change in mean open time. When KACh channels were activated independently of G-protein activation by 20 mM Na⁺, open probability was also inhibited by .Voltage-activated K⁺ currents and inward rectifying K⁺ currents were not affected by .These findings show that inhibition by and of KACh channels occurs at a level downstream of the action of Gβγ or Na⁺ on channel activation. The interference with phosphatidylinositol 4,5-bisphosphate (PIP2)-channel interaction can be suggested as a most plausible mechanism.