Electrical activity in rat tail artery during asynchronous activation of postganglionic nerve terminals by ciguatoxin-1.
1. The effects of ciguatoxin-1 (CTX-1) on the membrane potential of smooth muscle cells have been examined in rat proximal tail arteries isolated in vitro. 2. CTX-1 (> or = 10 pM) increased the frequency of spontaneous excitatory junction potentials (s.e.j.ps). At 100-400 pM, there was also a marked and maintained depolarization (19.7 +/- 1.4 mV, n = 14, at 400 pM). 3. In 20-400 pM CTX-1, perivascular stimuli evoked excitatory junction potentials (e.j.ps) which were prolonged in time course relative to control. 4. Although threshold and latency of the e.j.p. were not affected by CTX-1 (< or = 400 pM), propagated impulses were blocked at > or = 100 pM. 5. The spontaneous activity and the depolarization produced by CTX-1 were reduced in the presence of Ca2+ (0.1 mM)/Mg2+ (25 mM), omega-conotoxin (0.1 microM) or Cd2+ (50-100 microM). 6. All effects of CTX-1 were abolished by tetrodotoxin (0.3 microM). 7. Raised Ca2+ (6 mM) reduced the depolarization and spontaneous activity produced by CTX-1. 8. In 400 pM CTX-1, the membrane repolarized (17 +/- 3.2 mV, n = 4) following the addition of phentolamine (1 microM). S.e.j.ps and e.j.ps were selectively abolished by suramin (1 mM), and the membrane repolarized by 1.3 +/- 1.6 mV (n = 4). 9. We conclude that CTX-1 releases noradrenaline and ATP by initiating asynchronous discharge of postganglionic perivascular axons. In 100-400 pM CTX-1, the smooth muscle was depolarized to levels resembling those recorded in this artery during ongoing vasoconstrictor discharge in vivo.
Brock
J A
JA
Department of Physiology & Pharmacology, University of Queensland, Australia.
McLachlan
E M
EM
Jobling
P
P
Lewis
R J
RJ
D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D001369:Axons / Q000502:physiology; D002118:Calcium / Q000502:physiology; D002922:Ciguatoxins / Q000494:pharmacology*; D004558:Electric Stimulation; D004594:Electrophysiology; D005260:Female; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D009451:Neuroeffector Junction / Q000187:drug effects / Q000502:physiology*; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology*; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology; D012039:Regional Blood Flow / Q000187:drug effects; D013498:Suramin / Q000494:pharmacology; D013623:Tail / Q000098:blood supply; D013779:Tetrodotoxin / Q000494:pharmacology
D009467:Neuromuscular Depolarizing Agents; D011942:Receptors, Adrenergic, alpha; D002922:Ciguatoxins; D013779:Tetrodotoxin; D013498:Suramin; D008274:Magnesium; D002118:Calcium