TY - JOUR
T1 - Use of cytosolic metabolite patterns to estimate free magnesium in normoxic myocardium
AU - Mallet, Robert T.
AU - Kang, Young Hee
AU - Mukohara, Naoki
AU - Bünger, Rolf
N1 - Funding Information:
This study was supportedb y grants to RTM from Texas College of OsteopathicM edicine (34209)a nd to RB from the National Instituteso f Health CR01 HL-29060,R Ol HL-370671,t he Veterans Administration (G276CD), and the Uniformed ServicesU niversity of the Health Sciences (R07638). The expert technical assistanceo f Paul Konstant and Adelheid L. Weber and the secretariala ssistanceo f Michaela S. Geter are gratefullya cknowledged.
PY - 1992/7/7
Y1 - 1992/7/7
N2 - Cytosolic free magnesium (Mgf) is considered relatively constant. To test this concept, Mgf was estimated during hyperkalemic ventricular akinesis, normal and maximum adrenergic stimulation, and sulfate loading of the normoxic perfused guinea-pig heart. The Mgf estimates utilized a new sliding scale derived from the Mg2+-dependence of glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase (GAPDH/PGK). The pseudo constant KGAPDH′·KPGK′ was measured as ([creatine phosphate][3-phosphoglycerate][lactate]KLDH/([creatine][Pi[glyceraldehyde 3-phosphate][pyruvate]KCK), which varied with magnesium due to KCK (CK, LDH = creatine kinase, lactate dehydrogenase). However, the correct magnesium dependencies of the true constants KGAPDH·KPGK and KCK were taken from the literature. The [Mg2+] at which pseudo KGAPDH′·KPGK′ equalled true KGAPDH·KPGK was the best estimate of Mgf. Mgf fell to ≈0.13 mM in hyperkalemic arrest from a control of ≈0.6 mM, rising to ≈0.85 mM only during maximum adrenergic stress. Mgf increased further to ≈1.3 mM during sulfate loading which induced ATP catabolism. Mgf and ATP were reciprocally related. Thus; (1) myocardial free [Mg2+] judged from GAPDH/PGK mass-action relations changed appreciably only under extreme physiological states; (2) ATP was a major chelator of Mg2+ in perfused myocardium, i.e., acute ATP pool size reduction may be associated with increments in Mgf.
AB - Cytosolic free magnesium (Mgf) is considered relatively constant. To test this concept, Mgf was estimated during hyperkalemic ventricular akinesis, normal and maximum adrenergic stimulation, and sulfate loading of the normoxic perfused guinea-pig heart. The Mgf estimates utilized a new sliding scale derived from the Mg2+-dependence of glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase (GAPDH/PGK). The pseudo constant KGAPDH′·KPGK′ was measured as ([creatine phosphate][3-phosphoglycerate][lactate]KLDH/([creatine][Pi[glyceraldehyde 3-phosphate][pyruvate]KCK), which varied with magnesium due to KCK (CK, LDH = creatine kinase, lactate dehydrogenase). However, the correct magnesium dependencies of the true constants KGAPDH·KPGK and KCK were taken from the literature. The [Mg2+] at which pseudo KGAPDH′·KPGK′ equalled true KGAPDH·KPGK was the best estimate of Mgf. Mgf fell to ≈0.13 mM in hyperkalemic arrest from a control of ≈0.6 mM, rising to ≈0.85 mM only during maximum adrenergic stress. Mgf increased further to ≈1.3 mM during sulfate loading which induced ATP catabolism. Mgf and ATP were reciprocally related. Thus; (1) myocardial free [Mg2+] judged from GAPDH/PGK mass-action relations changed appreciably only under extreme physiological states; (2) ATP was a major chelator of Mg2+ in perfused myocardium, i.e., acute ATP pool size reduction may be associated with increments in Mgf.
KW - ATP phosphorylation potential
KW - Creatine kinase
KW - Cytosolic free magnesium
KW - Glyceraldehyde 3-phosphate dehydrogenase
KW - Guinea-pig myocardium
KW - Phosphoglycerate kinase
UR - http://www.scopus.com/inward/record.url?scp=0026725320&partnerID=8YFLogxK
U2 - 10.1016/0925-4439(92)90140-I
DO - 10.1016/0925-4439(92)90140-I
M3 - Article
C2 - 1627662
AN - SCOPUS:0026725320
SN - 0925-4439
VL - 1139
SP - 239
EP - 247
JO - Biochimica et Biophysica Acta - Molecular Basis of Disease
JF - Biochimica et Biophysica Acta - Molecular Basis of Disease
IS - 3
ER -