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THE EFFECTS OF CALCIUM AND MAGNESIUM IONS, TEMPERATURE AND REPETITIVE STIMULATION ON INHIBITORY JUNCTIONAL TRANSMISSION IN SMOOTH MUSCLE OF GUINEA‐PIG SMALL INTESTINE
Author(s) -
LANG RICHARD J.
Publication year - 1979
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.1476-5381.1979.tb16104.x
Subject(s) - calcium , magnesium , inhibitory postsynaptic potential , stimulation , chemistry , biophysics , guinea pig , amplitude , medicine , neuromuscular transmission , endocrinology , biology , physics , optics , organic chemistry
1 The effects of calcium and magnesium ions and temperature on the peak amplitude of the nonadrenergic, noncholinergic inhibitory junction potential, evoked by a single stimulus, or paired transmural stimuli, were examined in the circular muscle of guinea‐pig small intestine. 2 The peak amplitude of the inhibitory junction potential (i.j.p.) could be decreased by lowering the external concentration of calcium or by raising the external magnesium concentration (at 25°C). 3 At 25°C, the second of a pair of i.j.ps was larger than the first at short intervals (<0.2 s), but smaller at larger intervals (0.2 to 20 s). Enhancement of the second (test) response decayed exponentially with a time constant of 87 ms. Depression of the test i.j.p. was maximal at 0.4 s and then recovered exponentially with a time constant of 11 s. 4 In low calcium or high magnesium solution, depression of the test i.j.p. decreased without any change in the rate of recovery from depression. 5 Despite the slow rate of recovery from depression after a single conditioning response, transmitter output could be maintained during low‐frequency repetitive stimulation. 6 The peak amplitude of the i.j.p. increased as the temperature was raised to 35°C (Q 10 = 1.5). 7 In contrast to the neuromuscular junction, the depression of the second of a pair of i.j.ps decreased as the temperature was raised. At 35°C the test i.j.p. was larger than the conditioning i.j.p. for most stimulus intervals (1 to 20 s). 8 The results suggest that the rate of replenishment of the store of inhibitory transmitter is sensitive to both temperature and repetitive stimulation.