Early onset of a decreased intracellular magnesium and phosphate concentration in smooth muscle cell of SHR.

A decrease in total magnesium content is not a direct proof of a decreased magnesium ion concentration. It could reflect a phosphate alteration or an ATP metabolism disorder. Plasma phosphate levels are lower in spontaneously hypertensive rats (SHRs) than in Wistar-Kyoto rats (WKYs), and defects in membrane regulation or mitochondrial ATP synthase occur. Only sparse data exist concerning cellular magnesium and phosphate concentrations in hypertensive cells. In aortic smooth muscle cells from 10 SHRs of the Münster strain and 10 age-matched normotensive WKY rats, the intracellular phosphate and magnesium content was measured by electron probe X-ray microanalysis (Camscan CS 24 apparatus, Cambridge, U.K.). The Mg++ content was 0.09 +/- 0.15 g/kg dry weight in SHRs versus 1.15 +/- 0.10 g/kg dry weight in WKY rats (p < 0.01). Vascular smooth muscle phosphate content was 23.6 +/- 0.79 g/kg dry weight in WKY rats versus 15.81 +/- 1.22 g/kg dry weight in SHRs (p < 0.01). In aortic smooth muscle cells of one month old SHRs intracellular magnesium was measured as 1.05 +/- 0.08 versus 1.09 +/- 0.09 g/kg dry weight in WKYs. Intracellular phosphate concentration in one month old SHRs was 18.71 +/- 2.41 versus 21.36 +/- 1.25 g/kg dry weight in WKYs (eight animals in each group). Aortic smooth muscle cells of SHRs are caracterized by markedly lowered intracellular phosphate and magnesium concentrations, resulting in an altered ATP-metabolism, as described earlier. Possibly a membrane defect or a magnesium deficiency or disturbed magnesium channels are responsible for the early onset in the pathogenesis of primary hypertension.