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Presynaptic α 2 ‐autoinhibition in a vascular neuroeffector junction where ATP and noradrenaline act as co‐transmitters
Author(s) -
Bulloch J.M.,
Starke K.
Publication year - 1990
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.1476-5381.1990.tb14694.x
Subject(s) - vasoconstriction , yohimbine , prazosin , stimulation , chemistry , neurotransmission , purinergic receptor , medicine , endocrinology , biology , antagonist , receptor
1 α 2 ‐Autoinhibition of transmitter release was investigated in the largest rami caecales of the rabbit ileocolic artery. Vasoconstriction, elicited by electrical field stimulation or by exogenous agonists, was measured as an increase in perfusion pressure. 2 Short periods of electrical stimulation elicited monophasic vasoconstriction, whereas longer periods (>10s) produced biphasic vasoconstriction. Prazosin had no significant effect on the first component of the biphasic vasoconstriction elicited by electrical stimulation, but did reduce the second component at higher frequencies. α,β‐Methylene ATP significantly attenuated the first component whilst the second component was relatively resistant. 3 The α 2 ‐adrenoceptor antagonist yohimbine did not change responses evoked by very short pulse trains (< 2 s) but enhanced responses to longer pulse trains. When vasoconstriction was biphasic, both phases were potentiated by yohimbine. 4 The results indicate that the vasoconstriction elicited by brief trains of sympathetic nerve impulses is mainly or exclusively mediated by ATP, whereas at longer pulse trains a noradrenergic component comes into play. The potentiation produced by yohimbine is due to interruption of presynaptic α 2 ‐adrenoceptor‐mediated autoinhibition of transmitter release. The autoinhibition affects both purinergic and adrenergic components of sympathetic neurotransmission.