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Effects of prolonged application of isoprenaline on intracellular free magnesium concentration in isolated heart of rat
Author(s) -
Nishimura H.,
Matsubara T.,
Ikoma Y.,
Nakayama S.,
Sakamoto N.
Publication year - 1993
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.1476-5381.1993.tb13589.x
Subject(s) - isoprenaline , chemistry , propranolol , phosphocreatine , medicine , endocrinology , intracellular , stimulation , energy metabolism , biochemistry
1 The effect of prolonged application of isoprenaline on intracellular free‐Mg 2+ concentration ([Mg 2+ ] i ) was examined by use of 31 P‐nuclear magnetic resonance ( 31 P‐n.m.r.) in rat isolated hearts. Left ventricular pressure (LVP) was simultaneously measured. 2 [Mg 2+ ] i was estimated from the separation of the α‐ and β‐ATP peaks, using the dissociation constant of MgATP 38 μ m (established previously). In normal (phosphate‐free, Krebs‐Henseleit) solution, [Mg 2+ ] i was approximately 0.4 m m . 3 When isoprenaline was applied for 100 min, a transient increase in [Mg 2+ ] i was observed during the initial 25 min, whilst concentrations of ATP ([ATP]) and phosphocreatine ([PCr]) decreased and [P i ] correspondingly increased. During the subsequent 75 min of isoprenaline application, [Mg 2+ ] i decreased below its resting levels. Washout of isoprenaline restored [Mg 2+ ] i and [PCr], but [ATP] remained low. These changes elicited by isoprenaline were not observed in the presence of propranolol, a typical α‐adrenoceptor blocker. 4 Isoprenaline increased both LVP and heart rate. The increased LVP and heart rate slowly returned to lower values during prolonged application of isoprenaline, but remained higher than those before application. 5 The transient rise in [Mg 2+ ] i elicited by isoprenaline could be attributed to the decrease in [ATP] resulting in a release of Mg 2+ . The subsequent decrease in [Mg 2+ ] i during the prolonged applications suggests that β‐adrenoceptor stimulation itself facilitates Mg 2+ ‐extruding mechanism(s).