Cytosolic free magnesium in cardiac myocytes: identification of a Mg2+ influx pathway.
Regulation of intracellular Mg2+ activity in the heart is not well characterized. Cardiac myocytes were prepared as primary cultures from 7 day old chick embryo hearts and intracellular Mg2+ concentration [( Mg2+]i) was determined in single ventricular cells with mag-fura-2. Basal [Mg2+]i was 0.48 +/- 0.03 mM in normal culture medium. There was no correlation of basal [Mg2+]i with cellular contraction or intracellular [Ca2+]i (determined with fura-2). Cardiocytes cultured (16 hr) in low Mg (0.16 mM) media contained 0.21 +/- 0.05 mM Mg2+ which returned to normal levels when placed in Mg media with a refill time of 20 min. Basal [Ca2+]i (121 +/- 11 nM) and stimulated [Ca2+]i (231 +/- 41 nM) was similar to control cells. Verapamil, 25 microM, reversibly blocked Mg2+ refill. In conclusion, the basal [Mg2+]i of isolated cardiomyocytes is considerably below the Mg2+ electrochemical equilibrium allowing passive Mg2+ influx. The influx pathway for Mg2+ is inhibited by verapamil and appears to be independent of Ca2+ as assessed by fura-2.
Quamme
G A
GA
Department of Medicine, University of British Columbia University Hospital, Vancouver, Canada.
Rabkin
S W
SW
D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
D001572:Benzofurans; D005456:Fluorescent Dyes; D014700:Verapamil; D008274:Magnesium; D002118:Calcium; D016257:Fura-2