Assignment of muscarinic receptor subtypes mediating G-protein modulation of Ca(2+) channels by using knockout mice.
There are five known subtypes of muscarinic receptors (M(1)-M(5)). We have used knockout mice lacking the M(1), M(2), or M(4) receptors to determine which subtypes mediate modulation of voltage-gated Ca(2+) channels in mouse sympathetic neurons. Muscarinic agonists modulate N- and L-type Ca(2+) channels in these neurons through two distinct G-protein-mediated mechanisms. One pathway is fast and membrane-delimited and inhibits N- and P/Q-type channels by shifting their activation to more depolarized potentials. The other is slow and voltage-independent and uses a diffusible cytoplasmic messenger to inhibit both Ca(2+) channel types. Using patch-clamp methods on acutely dissociated sympathetic neurons, we isolated each pathway by pharmacological and kinetic means and found that each one is nearly absent in a particular knockout mouse. The fast and voltage-dependent pathway is lacking in the M(2) receptor knockout mice; the slow and voltage-independent pathway is absent from the M(1) receptor knockout mice; and neither pathway is affected in the M(4) receptor knockout mice. The knockout effects are clean and are apparently not accompanied by compensatory changes in other muscarinic receptors.
Shapiro
M S
MS
Department of Physiology and Biophysics, Box 357290, University of Washington School of Medicine, Seattle, WA 98195-7290, USA.
Loose
M D
MD
Hamilton
S E
SE
Nathanson
N M
NM
Gomeza
J
J
Wess
J
J
Hille
B
B
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D005033:Ethylmaleimide / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008954:Models, Biological; D010095:Oxotremorine / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011976:Receptors, Muscarinic / Q000145:classification*; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000378:metabolism
D015220:Calcium Channels; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D010095:Oxotremorine; D019204:GTP-Binding Proteins; D005033:Ethylmaleimide