The electrical and mechanical basis of co-transmission in some vascular and non-vascular smooth muscles.
1. The intracellularly-recorded electrical and mechanical responses to field stimulation of intramural nerves in three sympathetically-innervated smooth muscles--the mouse vas deferens, the rabbit ear artery and the rabbit mesenteric bed preparation were investigated. 2. In each tissue there was evidence for co-transmission involving noradrenaline (NA) and adenosine 5'-triphosphate (ATP) or a closely related nucleotide. 3. The electrical response in each tissue consisted of excitatory junction potentials (ejps) which were abolished by alpha, beta-methylene ATP (alpha, beta MeATP, 1-10 X 10(-6) M), suggesting that they were mediated by ATP. Only in the rabbit ear artery was there an additional electrical event mediated by NA. This took the form of a small slow membrane depolarization which followed the ejps and which was antagonized by either of the alpha-adrenoreceptor blocking agents phentolamine (1 X 10(-6) M) or prazosin (1 X 10(-7) M). 4. In the mouse vas deferens and rabbit mesenteric artery, both transmitter substances (NA and ATP) played a role in the contractile response to field stimulation. In the rabbit ear artery, NA alone appeared to mediate the contractile event. 5. Contractile responses to nerve-released ATP were accompanied by a membrane potential change, whereas those to NA appeared to be mediated largely by a voltage-independent mechanism. 6. In the mouse vas deferens, the ejps and action potentials evoked by field stimulation appeared to be mediated by a discrete increase in permeability to Na+ and K+. 7. In the mouse vas deferens, local application of bradykinin (1-100 X 10(-7) M) produced a small, slow membrane hyperpolarization. VIP (1-100 X 10(-7) M), neuropeptide Y (1-100 X 10(-7) M), substance P (1-100 X 10(-7) M), somatostatin (1-100 X 10(-7) M), leu-enkephalin (1-100 X 10(-7) M), metenkephalin (1-100 X 10(-7) M) and bombesin (1-100 X 10(-7) M), similarly applied, each produced no significant change in membrane potential. None of these peptides appear to be the transmitter mediating the ejp in this tissue.
Muir
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TC
Department of Pharmacology, University of Glasgow, UK.
Wardle
K A
KA
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000294:innervation; D009638:Norepinephrine / Q000494:pharmacology; D011817:Rabbits; D009435:Synaptic Transmission / Q000187:drug effects
D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D009638:Norepinephrine