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α 2 ‐Adrenergic hyperpolarization is not involved in slow synaptic inhibition in amphibian sympathetic ganglia
Author(s) -
Rafuse Paul E.,
Smith Peter A.
Publication year - 1986
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1986.tb10831.x
Subject(s) - yohimbine , prazosin , hyperpolarization (physics) , endocrinology , medicine , idazoxan , phentolamine , inhibitory postsynaptic potential , chemistry , postsynaptic potential , sucrose gap , guanethidine , depolarization , propranolol , receptor , biology , stimulation , stereochemistry , antagonist , nuclear magnetic resonance spectroscopy
1 The adrenaline‐induced hyperpolarization (Ad H ), slow inhibitory postsynaptic potential (slow i.p.s.p.) and hyperpolarizing phase of the response to methacholine (MCh H ) in Rana pipiens sympathetic ganglia were studied by means of the sucrose‐gap technique. 2 Desmethylimipramine (DMI, 0.5 μM) lowered the EC 50 for adrenaline from 1.65 μM (1.23–2.21 μM, n = 10) to 0.30 μM (0.21–0.41 μM, n = 8). DMI did not potentiate the slow i.p.s.p. or the MCh H . 3 Propranolol, sotalol or prazosin (1 μM) did not antagonize the Ad H . The response was antagonised by phentolamine (IC 50 = 0.53 μM), yohimbine (IC 50 = 6.2 nM) and idazoxan (IC 50 = 0.59 μM). Yohimbine (0.1 μM) did not reduce the amplitude of the slow i.p.s.p. or the MCh H . 4 The slow i.p.s.p. was eliminated in Ringer solution containing Cd 2+ (100 μM): This concentration of Cd 2+ did not reduce the amplitude of the MCh H . 5 α‐Methylnoradrenaline produced a concentration‐dependent hyperpolarization with an EC 50 of 0.31 μM (0.13–0.73 μM, n = 5), in the presence of DMI (0.5 μM). 6 These results are consistent with the hypothesis that the Ad H may be generated by activation of a receptor similar to the mammalian α 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.