Mg++/Na+ exchange and ratio in the spontaneously hypertensive rat (SHR)

Whereas in blood cells decreased magnesium concentrations and increased sodium concentrations in essential hypertension have often been described only sparse data exist on cellular magnesium or sodium content and exchange in vascular smooth muscle cells. Therefore the intracellular magnesium and sodium content was measured in aortic smooth muscle cells from 10 spontaneously hypertensive rats (SHR) of the Munster strain and 10 normotensive Wistar-Kyoto rats (WKY) aged 3 and 8-10 months. Electron-probe X-ray microanalysis was used to determine intracellular Mg++ and Na+ concentrations in aortic cryosections 3 mu m thick. Cellular magnesium ion content was 47 +/- 13 mmol/kg dry weight in SHR versus 48 +/- 19 mmol/kg dry weight in WKY aged 3 months and 37 +/- 6 mmol/kg dry weight in SHR versus 47 +/- 4 mmol/kg dry weight in WKY aged 8-10 months (p < 0.05). Vascular smooth muscle sodium ion content was 283 +/- 59 mmol/kg dry weight in WKY and 402 +/- 123 mmol/kg dry weight in SHR aged 3 months (p < 0.05) and 289 +/- 17 mmol/kg dry weight in WKY versus 548 +/- 39 mmol/kg dry weight in SHR aged 8-10 months (p < 0.05). Cellular Mg++ and Na+ handling may be disturbed in SHR aortic smooth muscle cells as it is in hypertensive blood cells. In addition, it is concluded that vascular smooth muscle cell Mg++/Na+ exchanger can be altered in a subgroup of SHR.