title: G protein-mediated inhibition of inwardly rectifying K+ channels in guinea pig chromaffin cells.
abstract: Properties of inwardly directed rectification and its G protein-mediated inhibition in guinea pig chromaffin cells were studied using the whole cell version of the patch-clamp technique. The current-voltage (I-V) relationship for plateau currents in response to a 50-ms pulse showed an inwardly directed rectification between -80 and -140 mV and a negative slope at more negative potentials in normal solution. Replacement of Na+ with N-methyl-D-glucamine (NMDG) in the perfusate did not alter the plateau I-V relationship between -110 and -130 mV but did abolish the negative slope below -140 mV. The zero current or resting membrane potential in the NMDG solution was in fair agreement with the equilibrium potential for K+. The chord conductance-voltage relationship showed a good fit with the Boltzmann equation and shifted along the voltage axis by an approximate change in driving force on K+ when K+ concentration was increased. External Cs+ and Ba2+ produced a voltage-dependent inhibition of the inwardly directed rectification. These results indicate that inwardly rectifying (IR) K+ channels are mediating an inwardly directed rectification. Intracellular dialysis with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) produced a complete suppression of this IR K+ channel, irrespective of treatment with pertussis toxin. Adding GTP or guanosine 5'-O-(2-thiodiphosphate) to the patch solution resulted in a decrease in GTP gamma S inhibition of the K+ current. Internal application of vanadate was without effect. Time course of the inhibition of the IR K+ current coincided in part with that of inactivation of a nonselective cation current. In conclusion, IR K+ channels in the chromaffin cell are subject to G protein-mediated inhibition.
authors.affiliation: Department of Physiology, School of Medicine, Fukuoka University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Inoue
authors.forename: I
authors.initials: I
authors.lastname: Imanaga
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D002586:Cesium / Q000494:pharmacology; D002838:Chromaffin System / Q000166:cytology / Q000378:metabolism*; D004553:Electric Conductivity; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006168:Guinea Pigs; D009994:Osmolar Concentration; D037342:Pertussis Toxin; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism / Q000502:physiology; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D026902:Potassium Channel Blockers; D015221:Potassium Channels; D010566:Virulence Factors, Bordetella; D002586:Cesium; D001464:Barium; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D011188:Potassium