Coupling of m2 and m4 muscarinic acetylcholine receptor subtypes to Ca(2+)-dependent K+ channels in transformed NL308 neuroblastoma x fibroblast hybrid cells.
Muscarinic acetylcholine receptor (mAChR) subtype (m1-m4)-specific cDNAs were transfected into NL308 neuroblastoma-fibroblast hybrid cells and clones expressing each of the individual mAChR subtypes m1, m2, m3 and m4 obtained. Acetylcholine increased phosphoinositide (PI) turnover in m1- and m3-transformed cells, but did not produce detectable changes in m2- and m4-transformed cells. In cells expressing m1 and m3 subtypes, ACh produced an initial outward K+ current, followed by a cationic current. In cells expressing m2 and m4 receptors, only the initial K+ current was detected. The outward currents were associated with a rise in intracellular Ca2+ as measured with Fura-2 or Indo-1, and were inhibited by chelating intracellular Ca2+ with external BAPTA-AM, or by external charybdotoxin or Ba2+: hence they were attributed to the activation of a Ca(2+)-dependent K+ current. However, the outward current produced in m2- and m4-transformed cells was blocked by pretreatment with 5 ng ml-1 Pertussis toxin (PTX), whereas that in m1- and m3-transformed cells was not. These results suggest that m2- and m4-receptors in transformed NL308 cells coupled to PTX-sensitive G-protein which is capable of mobilizing intracellular Ca2+ and activate IK(Ca), whereas m1 and m3 receptors activate a similar process through a different, PTX-insensitive G-protein.
Noda
M
M
Department of Biophysics, Kanazawa University School of Medicine, Japan.
Katayama
M
M
Brown
D A
DA
Robbins
J
J
Marsh
S J
SJ
Ishizaka
N
N
Fukuda
K
K
Hoshi
N
N
Yokoyama
S
S
Higashida
H
H
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D002614:Chelating Agents / Q000494:pharmacology; D004247:DNA / Q000235:genetics; D005347:Fibroblasts; D019204:GTP-Binding Proteins / Q000378:metabolism; D006822:Hybrid Cells / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009447:Neuroblastoma; D037342:Pertussis Toxin; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013539:Simian virus 40 / Q000235:genetics; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D002614:Chelating Agents; D015221:Potassium Channels; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D001464:Barium; D011813:Quinuclidinyl Benzilate; D004247:DNA; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000109:Acetylcholine; D002118:Calcium