Premium
The role of Na + in muscarinic receptor‐mediated catecholamine secretion in the absence of extracellular Ca 2+ in cat perfused adrenal glands
Author(s) -
Teraoka Hiroki,
Yamada Yutaka,
Nakazato Yoshikazu,
Ohga Akira
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.tb12090.x
Subject(s) - veratridine , ouabain , pilocarpine , muscarinic acetylcholine receptor , hexamethonium , endocrinology , acetylcholine , catecholamine , medicine , extracellular , chemistry , secretion , adrenal medulla , tetrodotoxin , receptor , biology , sodium , biochemistry , sodium channel , organic chemistry , neuroscience , epilepsy
1 The role of Na + in muscarinic receptor‐mediated catecholamine secretion, which is independent of extracellular Ca 2+ , was investigated by observing the effect of veratridine and ouabain in perfused adrenal glands of the cat. 2 Veratridine (10 −4 m ) markedly enhanced catecholamine secretion evoked by acetylcholine (ACh, 10 −4 m ) during perfusion with Ca 2+ ‐free Locke solution containing hexamethonium (10 −3 m ). The enhancement tended to be larger for noradrenaline secretion than for adrenaline secretion. Qualitatively the same result was obtained in the response to pilocarpine (5 × 10 −4 m ). 3 Ouabain (10 −4 m ) also enhanced ACh‐ and pilocarpine‐induced catecholamine secretions, especially noradrenaline secretion in the absence of extracellular Ca 2+ . 4 Tetrodotoxin (10 −6 m ) blocked the enhancing effect of veratridine on ACh‐induced catecholamine secretion, but not that of ouabain in the absence of extracellular Ca 2+ . 5 When NaCl was replaced with sucrose, there was no secretory response to ACh regardless of the presence or absence of veratridine or ouabain. However, when ouabain, but not veratridine, was infused with Na + before the replacement of NaCl, the response to ACh was substantially augmented. 6 These results indicate that Na + is essential in the initiation of muscarinic receptor‐mediated catecholamine secretion and its enhancement by veratridine and ouabain in the absence of extracellular Ca 2+ . Both drugs seem to increase the intracellular concentration of Na + through different mechanisms and result in increases in the efficiency of Ca 2+ mobilization from intracellular Ca 2+ pools linked to muscarinic receptors.