Cloned muscarinic receptor subtypes expressed in A9 L cells differ in their coupling to electrical responses.
The electrophysiological responses to cholinergic stimulation of four cloned muscarinic receptor subtypes (m1-m4) were studied in A9 L cells transfected with the expression plasmids of each of the different subtypes, using the tight-seal whole-cell recording technique. Cells transfected with m1 and m3 muscarinic receptor subtypes were hyperpolarized by acetylcholine (ACh), whereas m2- and m4-transfected cells did not respond to ACh concentrations of up to 1 mM. Stimulation of both m1 and m3 muscarinic receptor subtypes evoked outward currents in cells voltage-clamped at -50 mV, associated with an increase in membrane conductance. These outward currents were blocked by atropine but not by tubocurarine. The ACh-induced currents of m1- and m3-transfected cells primarily involved potassium ions, although chloride ions also contributed to a minor extent. The potassium and chloride conductances were blocked by barium or cobalt and by buffering the intracellular calcium to low levels with 5 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid, showing a dependence of these conductances on calcium. Thus, m1- and m3-transfected cells respond to ACh in a manner that is qualitatively similar, evoking calcium-dependent potassium and chloride conductances, whereas m2- and m4-transfected cells are not coupled to electrically detectable responses in A9 L cells.
Jones
S V
SV
Laboratory of Neurophysiology, National Institute of Neurological and Communicative Disorders and Stroke, Bethesda, Maryland 20892.
Barker
J L
JL
Buckley
N J
NJ
Bonner
T I
TI
Collins
R M
RM
Brann
M R
MR
D000109:Acetylcholine / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology; D002712:Chlorides / Q000502:physiology; D003001:Cloning, Molecular; D004553:Electric Conductivity; D004594:Electrophysiology; D006801:Humans; D007739:L Cells; D011188:Potassium / Q000502:physiology; D051381:Rats; D011976:Receptors, Muscarinic / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D014162:Transfection
D002712:Chlorides; D011976:Receptors, Muscarinic; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium