Intracellular free magnesium and high energy phosphates in the perfused normotensive and spontaneously hypertensive at heart a31p nmr study

Abstract

We have employed31P nuclear magnetic resonance (NMR) spectroscopy to examine the relationship be­tween cytosolic free Mg2+ ([Mg2+], intracellular pH, high energy phosphates, and genetic hyperten­sion using the Wistar-Kyoto rat (WKY) as a control and the spontaneously hypertensive rat (SHR) as a model for essential hypertension. The mean systolic blood pressures (measured using the tail cuff method) of control and hypertensive rats (aged 7 to 12 weeks) were 113 ± 4 mm Hg (mean ± 2 SE, n = 14) and 162 ± 5 mm Hg (mean ± 2 SE, n = 17), re­spectively. Intracellular free Mg2+ levels were sig­nificantly depleted in the isolated Langendorff perfused hypertensive rat hearts (452 ± 39 /miol/L, mean ± 2 SE, n = 17) compared to control hearts (756 ± 52 /miol/L, n = 14); however, intracellular pH did not differ in the SHR hearts (7.02 ± 0.03, mean ± 2 SE, n = 7) compared with controls (7.03 ± 0.03, n = 7). Although we could not demonstrate a statisti­cally significant difference in the levels of P-crea- tine or ATP, intracellular P£ was two-fold higher (5.71 ± 2.28 mmol/L v 2.92 ± 0.66 mmol/L, n = 4) and the phosphorylation potential, [MgATP]/[MgADP][Pj], was correspondingly lower (3.0 X 104 ± 1.6 X 104 v 8.3 X 104 ± 1.4 X 104 (mol/L)-1, n = 4) in SHR compared to WKY hearts. These data demonstrate free magnesium depletion in heart muscle and indicate an alteration in cardiac bioen­ergetics in essential hypertension. © 1991 by the American Journal of Hypertension, Inc.