Intrinsic gating properties of a cloned G protein-activated inward rectifier K+ channel.
The voltage-, time-, and K(+)-dependent properties of a G protein-activated inwardly rectifying K+ channel (GIRK1/KGA/Kir3.1) cloned from rat atrium were studied in Xenopus oocytes under two-electrode voltage clamp. During maintained G protein activation and in the presence of high external K+ (VK = 0 mV), voltage jumps from VK to negative membrane potentials activated inward GIRK1 K+ currents with three distinct time-resolved current components. GIRK1 current activation consisted of an instantaneous component that was followed by two components with time constants tau f approximately 50 ms and tau s approximately 400 ms. These activation time constants were weakly voltage dependent, increasing approximately twofold with maximal hyperpolarization from VK. Voltage-dependent GIRK1 availability, revealed by tail currents at -80 mV after long prepulses, was greatest at potentials negative to VK and declined to a plateau of approximately half the maximal level at positive voltages. Voltage-dependent GIRK1 availability shifted with VK and was half maximal at VK -20 mV; the equivalent gating charge was approximately 1.6 e-. The voltage-dependent gating parameters of GIRK1 did not significantly differ for G protein activation by three heterologously expressed signaling pathways: m2 muscarinic receptors, serotonin 1A receptors, or G protein beta 1 gamma 2 subunits. Voltage dependence was also unaffected by agonist concentration. These results indicate that the voltage-dependent gating properties of GIRK1 are not due to extrinsic factors such as agonist-receptor interactions and G protein-channel coupling, but instead are analogous to the intrinsic gating behaviors of other inwardly rectifying K+ channels.
D000818:Animals; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D004594:Electrophysiology; D005260:Female; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D019204:GTP-Binding Proteins / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009865:Oocytes / Q000166:cytology / Q000502:physiology / Q000648:ultrastructure; D015221:Potassium Channels / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D011976:Receptors, Muscarinic / Q000032:analysis / Q000502:physiology; D011985:Receptors, Serotonin / Q000032:analysis / Q000502:physiology; D013997:Time Factors; D014982:Xenopus laevis
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011976:Receptors, Muscarinic; D011985:Receptors, Serotonin; D019204:GTP-Binding Proteins