Multiple calcium channels regulate neurotransmitter release from vagus nerve terminals in the cat bronchiole.
1. Twitch-like contractions and non-adrenergic non-cholinergic (NANC) relaxations evoked by electrical field stimulation (EFS) of the cat bronchiole were used to examine the voltage-activated calcium channels involved in excitatory and inhibitory neurotransmission in the cat bronchiole. 2. Nifedipine (50 microM), the L-type calcium channel antagonist, did not affect the twitch-like contraction and NANC relaxations. However, low concentrations of the N-type calcium channel blocker omega-conotoxin GVIA (omega-CgTX GVIA) (0.1 microM) irreversibly abolished twitch-like contractions evoked by trains of EFS </=10 stimuli at 20 Hz. 3. After the prolonged treatment with 0.1 microM omega-CgTX GVIA, EFS evoked initial fast and later slow NANC relaxations in the presence of 5-HT (10 microM), atropine and guanethidine (1 microM each). However increased concentration of omega-CgTX GVIA (1 microM) completely suppressed the slow NANC relaxation without affecting the initial fast component. 4. omega-agatoxin IVA (100 nM), the P- and Q-type calcium channel inhibitor, and nimodipine (10 microM), the L- and T-type calcium channel blocker, did not affect the amplitude of the initial fast NANC relaxation in the absence or presence of omega-CgTX GVIA (1 microM). 5. The contraction or relaxation induced by exogenous acetylcholine (ACh) (0.5 microM) or the nitric oxide donor, s-nitroso-N-acetyl penicillamine (SNAP) (1 microM) were not affected by omega-CgTX GVIA (1 microM). 6. Taken together, these results suggest that generation of twitch-like contraction and later slow NANC relaxation are regulated by N-type calcium channels, whereas generation of the initial fast NANC relaxation possibly involves R-type calcium channel.
Fujisawa
K
K
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka 812-8585, Japan.
Onoue
H
H
Abe
K
K
Ito
Y
Y
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001980:Bronchi / Q000166:cytology / Q000187:drug effects / Q000294:innervation* / Q000502:physiology; D002104:Cadmium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D002415:Cats; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014630:Vagus Nerve / Q000378:metabolism*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018377:Neurotransmitter Agents; C110881:S-nitro-N-acetylpenicillamine; D002104:Cadmium; D012701:Serotonin; D013779:Tetrodotoxin; D010396:Penicillamine; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester