Positive cooperativity in activation of the cardiac muscarinic K+ channel by intracellular GTP.
Concentration-dependent effects of intracellular GTP on activation of the muscarinic K+ channel were examined in inside-out patches of cardiac atrial myocytes. The pipette solution contained 0.1 microM ACh. GTP (0.01-30 microM) and 0.5 mM MgCl2 were applied to the inside side of the patch membrane. K+ channels were activated with GTP concentration above 0.1 microM. Channel activation reached a maximal value with 1-3 microM GTP. It decreased at GTP concentrations larger than 3 microM, probably due to desensitization. The dependence of the open probability of the channel on intracellular GTP showed a sigmoidal relationship with a Hill coefficient of around 3. A positive cooperative effect of intracellular GTP on the K+ channel may play an important role in amplifying the signal from the membrane receptor to the K+ channel.
Kurachi
Y
Y
Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Ito
H
H
Sugimoto
T
T
D000818:Animals; D004553:Electric Conductivity; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006168:Guinea Pigs; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*
D015221:Potassium Channels; D011976:Receptors, Muscarinic; D006160:Guanosine Triphosphate