Author(s): Fatholahi M, LaNoue K, Romani A, Scarpa A
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Abstract The changes in total Mg were compared with changes in cytosolic free Mg(2+) during metabolic stimulation of collagenase-dispersed rat cardiac myocytes or Langendorff-perfused rat hearts. In myocytes the addition of agents leading to cAMP increase or protein kinase C activation results in a loss or gain of more than 5\% of total Mg content within 3 min (i.e., 3-4 nmol Mg/mg protein). Under the same conditions, changes in cytosolic free Mg(2+) measured with fluorescent indicator are small and result in changes of cytosolic free Mg(2+) equivalent to 90-140 microM. In perfused hearts, beta-adrenergic stimulation results in a loss of total Mg larger than 0.5 micromol per gram of heart corresponding to 9\% loss of total Mg content of the heart (estimated to be 5.8 micromol). Under these conditions there is no change in cytosolic free Mg(2+) or the major buffer of cytosolic Mg(2+), ATP, as measured by (31)P NMR. These data suggest that a major redistribution of total Mg occurs in intracellular organelles or in cytosolic buffers in order to maintain cytosolic free Mg(2+) relatively unchanged during the observed cellular massive translocation of total Mg. Hence, Mg(2+) may regulate metabolic functions not within the cytosol but in locations where its concentration oscillates, such as extracellular fluid and intracellular compartments. Copyright 2000 Academic Press.
This article was published in Arch Biochem Biophys
and referenced in Journal of Microbial & Biochemical Technology