Differential blockade by nifedipine and omega-conotoxin GVIA of alpha 1- and beta 1-adrenoceptor-controlled calcium channels on motor nerve terminals of the rat.
Electrically evoked release of [3H]acetylcholine ([3H]ACh) from the rat phrenic nerve and its facilitation by stimulation of presynaptic alpha 1- and beta 1-adrenoceptors were investigated in the absence and presence of nifedipine and omega-conotoxin GVIA. Both calcium channel antagonists did not modify electrically evoked [3H]ACh release, but selectively blocked the effect triggered by both facilitatory adrenergic receptors. The increase in [3H]ACh release mediated via beta 1-adrenoceptor activation was abolished by low concentrations (1 nM) of omega-conotoxin GVIA, whereas nifedipine (100 nM) abolished the facilitatory effect mediated via alpha 1-adrenoceptor stimulation. Therefore, the beta 1-adrenoceptor is apparently coupled to a calcium channel that can be regarded as of the N-type, and the alpha 1-adrenoceptor is apparently coupled to a calcium channel that appears as a subtype of the L-type which is not sensitive to omega-conotoxin GVIA.
Wessler
I
I
Department of Pharmacology, University of Mainz, F.R.G.
Dooley
D J
DJ
Osswald
H
H
Schlemmer
F
F
D000109:Acetylcholine / Q000378:metabolism / Q000502:physiology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008978:Mollusk Venoms / Q000494:pharmacology*; D009045:Motor Endplate / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology*; D010791:Phrenic Nerve / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000187:drug effects* / Q000378:metabolism; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008978:Mollusk Venoms; D011941:Receptors, Adrenergic; D020866:omega-Conotoxin GVIA; D009543:Nifedipine; D000109:Acetylcholine