ATP-dependent desensitization of the muscarinic K+ channel in rat atrial cells.
1. Fast desensitization of the muscarinic K+ channel has been studied in excised patches from rat atrial cells. 2. In inside-out patches, ACh was present in the pipette and GTP was applied via the bath to activate the channel. In outside-out patches, GTP was present in the pipette and ACh was applied via the bath to activate the channel. In both cases, during a 30 s exposure to GTP or ACh there was a decline in channel activity as a result of fast desensitization if ATP was present. 3. In inside-out patches, fast desensitization was still observed if the muscarinic ACh receptor was bypassed and the channel was activated by GTP gamma S. This suggests that fast desensitization is a result of a modification of the channel (or the connecting G protein) and not the receptor. 4. In both inside-out and outside-out patches, channel activity was depressed and fast desensitization was reduced or absent, if ATP was not present. 5. The non-hydrolysable analogue of ATP, AMP-PNP, did not substitute for ATP in its effects on the channel. 6. The results are consistent with the hypothesis that fast desensitization of the muscarinic K+ channel is the result of a dephosphorylation of the channel.
Shui
Z
Z
Department of Physiology, University of Leeds, UK.
Boyett
M R
MR
Zang
W J
WJ
D000109:Acetylcholine / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D004594:Electrophysiology; D005459:Fluorides / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006325:Heart Atria; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D011976:Receptors, Muscarinic / Q000502:physiology*; D014638:Vanadates / Q000494:pharmacology; D015032:Zinc / Q000494:pharmacology
D015221:Potassium Channels; D011976:Receptors, Muscarinic; D000266:Adenylyl Imidodiphosphate; D014638:Vanadates; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D010744:Phosphoric Monoester Hydrolases; D015032:Zinc; D000109:Acetylcholine; D005459:Fluorides