Alpha 2-adrenergic hyperpolarization is not involved in slow synaptic inhibition in amphibian sympathetic ganglia.
The adrenaline-induced hyperpolarization (AdH), slow inhibitory postsynaptic potential (slow i.p.s.p.) and hyperpolarizing phase of the response to methacholine (MChH) in Rana pipiens sympathetic ganglia were studied by means of the sucrose-gap technique. Desmethylimipramine (DMI, 0.5 microM) lowered the EC50 for adrenaline from 1.65 microM (1.23-2.21 microM, n = 10) to 0.30 microM (0.21-0.41 microM, n = 8). DMI did not potentiate the slow i.p.s.p. or the MChH. Propranolol, sotalol or prazosin (1 microM) did not antagonize the AdH. The response was antagonised by phentolamine (IC50 = 0.53 microM), yohimbine (IC50 = 6.2 nM) and idazoxan (IC50 = 0.59 microM). Yohimbine (0.1 microM) did not reduce the amplitude of the slow i.p.s.p. or the MChH. The slow i.p.s.p. was eliminated in Ringer solution containing Cd2+ (100 microM). This concentration of Cd2+ did not reduce the amplitude of the MChH. Alpha-Methylnoradrenaline produced a concentration-dependent hyperpolarization with an EC50 of 0.31 microM (0.13-0.73 microM, n = 5), in the presence of DMI (0.5 microM). These results are consistent with the hypothesis that the AdH may be generated by activation of a receptor similar to the mammalian alpha 2-adrenoceptor. No evidence was found in support of the hypothesis that an adrenergic interneurone is involved in the synaptic pathway for the slow i.p.s.p.
Rafuse
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D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D003891:Desipramine / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D005728:Ganglia, Sympathetic / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D011894:Rana pipiens; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D008688:Methacholine Compounds; D011942:Receptors, Adrenergic, alpha; D002104:Cadmium; D016210:Methacholine Chloride; D015016:Yohimbine; D003891:Desipramine; D004837:Epinephrine