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Importance of magnesium and potassium concentration on basal tone and 5‐HT‐induced contractions in canine isolated coronary artery
Author(s) -
Murakawa Toshisuke,
Altura Bella T.,
Carella Anthony,
Altura Burton M.
Publication year - 1988
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.1476-5381.1988.tb11534.x
Subject(s) - basal (medicine) , magnesium , potassium , medicine , cardiology , endocrinology , chemistry , biology , organic chemistry , insulin
1 In vitro studies were undertaken to investigate the effects of external potassium ([K + ] o ) and magnesium ([Mg 2+ ] o ) concentration on canine coronary arterial basal tone and on 5‐hydroxytryptamine (5‐HT)‐induced contractions. 2 Acute withdrawal of, or reduction in, [K + ] o produced relaxation of basal tone in isolated coronary arteries, whereas acute withdrawal (but not reduction) of [Mg 2+ ] o produced contraction of these blood vessels. 3 The magnitude of coronary contraction obtained on withdrawal of [Mg 2+ ] o was dependent upon the [K + ] o ; the higher the [K + ] o , the greater the contraction. 4 The precise ratio of [K + ] o /[Mg 2+ ] o appeared to be important in dictating the degree of contraction (maximum response) and sensitivity (EC 50 ) of canine coronary vascular smooth muscle cells to 5‐HT. The EC 50 to 5‐HT was enhanced by increases in the [K + ] o /[Mg 2+ ] o ratio, whereas the ability of 5‐HT to induce a maximal contraction was attenuated by decreases in the [K + ] o ; the latter being modulated by [Mg 2+ ] o . Small changes in [Mg 2+ ] o could effect large changes in the EC 50 as [K + ] o was lowered. 5 These actions took place over patho‐physiological ranges of [K + ] o and [Mg 2+ ] o . 6 Maintenance of a constant [K + ] o /[Mg 2+ ] o ratio, irrespective of the exact [K + ] o and [Mg 2+ ] o , produced similar degrees of maximum tension. 7 Use of intact vascular ring preparations and helically‐cut vascular strips produced similar results with varying [K + ] o /[Mg 2+ ] o . 8 A variety of pharmacological receptor antagonists (phentolamine, propranolol, atropine, diphenhydramine, cimetidine), as well as a prostaglandin cyclo‐oxygenase inhibitor, did not modify the altered contractile responses or basal tone evoked by varying [K + ] o /[Mg 2+ ] o ratios. 9 These results suggest: (1) that basal tone and contractility of canine coronary vascular smooth muscle cells appear to be exquisitely sensitive to alterations in extracellular K + and Mg 2+ ; and (2) 5‐HT receptor‐operated Ca 2+ channels, as well as those Ca 2+ channels involved in generation of coronary arterial basal tone are modulated and controlled by the precise concentrations of [K + ] o and [Mg 2+ ] o .