Increased Na+ and decreased Mg2+ intracellular concentrations in vascular smooth muscle cells from spontaneously hypertensive rats

1. Although 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. 2. Therefore 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, the intracellular magnesium and sodium content was measured. 3. Electron-probe X-ray microanalysis was used to determine intracellular Mg2+ and Na+ concentrations in aortic cryosections 3 mu m thick. The Mg2+ 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 Nat 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 weighs in SHR aged 8-10 months (P < 0.05). 4. Aortic smooth muscle cells from SHR are characterized by a markedly lower intracellular Mg2+ content in 8-10-month-old animals and increased Na+ concentrations compared with normotensive cells in 3- and 8-10-month-old rats. The results may be due to genetically determined disturbances in transmembrane Mg2+ and Nat transport. Cellular magnesium and sodium handling may be disturbed in SHR aortic smooth muscle as it is in hypertensive blood cells. In addition, it is concluded that vascular smooth muscle cell Mg2+-Na+ exchanger can be altered in a subgroup of SHR.