Inhibition of ATP-induced increase in muscarinic K+ current by trypsin, alkaline pH, and anions.
In atrial cells, the open probability of G protein-activated ACh-sensitive K+ (KACh) channels can be increased approximately fivefold by intracellular ATP (ATPi). Using inside-out patches, we examined how proteases, changes in intracellular pH, and different anions affect G protein-mediated activation and ATP-induced stimulation of the KACh channel. Treatment with trypsin (0.5 mg/ml) removed the GTP dependence of the KACh channel and abolished the ATP-induced stimulation. Intracellular GTP activated KACh channels at all intracellular pH values tested (6.0-8.0), with the concentration at which half-maximal activation (K1/2) occurred ranging from 0.3 (pH 8.0) to 6.7 (pH 6.0) microM. However, the ATPi-induced increase in KACh channel activity was inhibited at pH 8. 0 (K1/2 = pH 7.4). All anions tested except sulfate, phosphate, fluoride, and iodide supported GTP-induced activation. Of the anions that supported GTP-induced activation, only citrate blocked the ATP-induced stimulation of the KACh channel. These results indicate that the GTP- and ATP-mediated effects on the KACh channel use separate signaling pathways. The ATP-mediated effect involves a trypsin- and pH-sensitive mechanism.
Department of Physiology and Biophysics, Finch University of Health Sciences, The Chicago Medical School, North Chicago, Illinois 60064, USA.
A
A
Pleumsamran
M L
ML
Wolak
D
D
Kim
D000109:Acetylcholine / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D000838:Anions; D019343:Citric Acid / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D015398:Signal Transduction; D055672:Static Electricity; D014357:Trypsin / Q000494:pharmacology*
D000838:Anions; D015221:Potassium Channels; D019343:Citric Acid; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D014357:Trypsin; D000109:Acetylcholine