On the mechanism of G protein beta gamma subunit activation of the muscarinic K+ channel in guinea pig atrial cell membrane. Comparison with the ATP-sensitive K+ channel.
Open Access
- 1 June 1992
- journal article
- research article
- Published by Rockefeller University Press in The Journal of general physiology
- Vol. 99 (6) , 961-983
- https://doi.org/10.1085/jgp.99.6.961
Abstract
The mechanism of G protein beta gamma subunit (G beta gamma)-induced activation of the muscarinic K+ channel (KACh) in the guinea pig atrial cell membrane was examined using the inside-out patch clamp technique. G beta gamma and GTP-gamma S-bound alpha subunits (G alpha *9s) of pertussis toxin (PT)-sensitive G proteins were purified from bovine brain. Either in the presence or absence of Mg2+, G beta gamma activated the KACh channel in a concentration-dependent fashion. 10 nM G beta gamma almost fully activated the channel in 132 of 134 patches (98.5%). The G beta gamma-induced maximal channel activity was equivalent to or sometimes larger than the GTP-gamma S-induced one. Half-maximal activation occurred at approximately 6 nM G beta gamma. Detergent (CHAPS) and boiled G beta gamma preparation could not activate the KACh channel. G beta gamma suspended by Lubrol PX instead of CHAPS also activated the channel. Even when G beta gamma was pretreated in Mg(2+)-free EDTA internal solution containing GDP analogues (24-48 h) to inactivate possibly contaminating G i alpha *9s, the G beta gamma activated the channel. Furthermore, G beta gamma preincubated with excessive GDP-bound G o alpha did not activate the channel. These results indicate that G beta gamma itself, but neither the detergent CHAPS nor contaminating G i alpha *, activates the KACh channel. Three different kinds of G i alpha * at 10 pM-10 nM could weakly activate the KACh channel. However, they were effective only in 40 of 124 patches (32.2%) and their maximal channel activation was approximately 20% of that induced by GTP-gamma S or G beta gamma. Thus, G i alpha * activation of the KACh channel may not be significant. On the other hand, G i alpha *9s effectively activated the ATP-sensitive K+ channel (KATP) in the ventricular cell membrane when the KATP channel was maintained phosphorylated by the internal solution containing 100 microM Mg.ATP. G beta gamma inhibited adenosine or mACh receptor-mediated, intracellular GTP-induced activation of the KATP channel. G i alpha *9s also activated the phosphorylated KATP channel in the atrial cell membrane, but did not affect the background KACh channel. G beta gamma subsequently applied to the same patch caused prominent KACh channel activation. The above results may indicate two distinct regulatory systems of cardiac K+ channels by PT-sensitive G proteins: G i alpha activation of the KATP channel and G beta gamma activation of the KACh channel.Keywords
This publication has 42 references indexed in Scilit:
- Ionic Channels and Their Regulation by G Protein SubunitsAnnual Review of Physiology, 1990
- Heart Rate Regulation by G Proteins Acting on the Cardiac Pacemaker ChannelScience, 1990
- Coupling of ATP-sensitive K+ channels to A1 receptors by G proteins in rat ventricular myocytesAmerican Journal of Physiology-Heart and Circulatory Physiology, 1990
- Beta gamma dimers of G proteins inhibit atrial muscarinic K+ channels.Journal of Biological Chemistry, 1990
- Purification and characterization of five different α subunits of guanine‐nucleotide‐binding proteins in bovine brain membranesEuropean Journal of Biochemistry, 1990
- Detergents, dimeric G beta gamma, and eicosanoid pathways to muscarinic atrial K+ channelsAmerican Journal of Physiology-Heart and Circulatory Physiology, 1990
- Positive cooperativity in activation of the cardiac muscarinic K+ channel by intracellular GTPPflügers Archiv - European Journal of Physiology, 1990
- β-Adrenergic Inhibition of Cardiac Sodium Channels by Dual G-Protein PathwaysScience, 1989
- Voltage‐dependent magnesium block of adenosine‐triphosphate‐sensitive potassium channel in guinea‐pig ventricular cells.The Journal of Physiology, 1987
- Effects of guanine nucleotides and Mg on human erythrocyte Ni and Ns, the regulatory components of adenylyl cyclase.Journal of Biological Chemistry, 1984