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Mechanical and electrical responses to α‐adrenoceptor activation in the circular muscle of guinea‐pig stomach
Author(s) -
Chihara S.,
Tomita T.
Publication year - 1987
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.1476-5381.1987.tb11277.x
Subject(s) - prazosin , contraction (grammar) , yohimbine , medicine , endocrinology , muscle contraction , chemistry , propranolol , phenylephrine , membrane potential , depolarization , biophysics , sucrose gap , tonic (physiology) , receptor potential , myogenic contraction , guinea pig , inhibitory postsynaptic potential , receptor , biology , antagonist , smooth muscle , blood pressure
1 In the circular muscle of the corpus region of the guinea‐pig stomach, the effects of catecholamines on mechanical activity were studied with simultaneous recording of membrane potential by use of intracellular microelectrodes. In order to investigate responses mediated through α‐adrenoceptors, the β‐adrenoceptors were blocked by propranolol (10 −6 m ) in most experiments. 2 Adrenaline (< 10 −6 m ) produced a monophasic contraction with little change in membrane potential. At higher concentrations (> 10 −5 m ), adrenaline usually produced an early transient contraction followed by a slow tonic contraction. During the early phase, the membrane was hyperpolarized and slow waves were reduced in amplitude. 3 The phasic contractions superimposed on the late slow phase of the contractile response were higher in frequency and larger in amplitude than in controls before adrenaline application. These changes were associated with an increase in the amplitude and frequency of slow waves, and with a spike‐like component appearing on the top of each slow wave. 4 Adrenaline‐induced changes in mechanical and electrical activity were inhibited by prazosin, but largely unaffected by yohimbine. In some preparations, there was a transient weak inhibition of phasic contraction before muscle tone was increased by adrenaline, and this became more pronounced in the presence of yohimbine. 5 Phenylephrine, selective for α 1 ‐receptors, produced responses very similar to those of adrenaline, whereas agonists selective for α 2 ‐receptors, clonidine and B‐HT 920, produced only a small slow contraction without any clear change in membrane potential. 6 It is concluded that in the circular muscle of guinea‐pig stomach, the contractile response and changes in the electrical slow wave activity produced by adrenaline are both mediated mainly through the activation of α 1 ‐receptors.