Cellular ions in hypertension, insulin resistance, obesity, and diabetes: a unifying theme

The clinical linkage of hypertensive cardiovascular disease, left ventricular hypertrophy, and accelerated atherosclerosis with a spectrum of metabolic disturbances including peripheral insulin resistance, hyperinsulinemia, obesity, and frank non-insulin dependent diabetes mellitus, has been increasingly appreciated. However, the underlying biologic basis mediating this clinical association remains unclear. Nuclear magnetic resonance techniques have been used to measure various intracellular ion species in human erythrocytes and have found that common, shared intracellular abnormalities of cytosolic free calcium, free magnesium, and pH occur in each of these clinical syndromes. Specifically, essential hypertension is characterized by higher fasting free cytosolic calcium concentrations and reciprocally lower intracellular free magnesium and pH levels compared with those of normotensive control subjects. Furthermore, for all subjects, free calcium and free magnesium levels were closely related both to the left ventricular mass and to the degree of insulin resistance present. Moreover, these same intracellular ionic lesions were found in normotensive obese and/or non-insulin diabetic individuals. Last, evidence has recently been provided that the cardiovascular consequences of increased dietary sugar and salt intake may well be determined by their concurrent influence on cellular ion metabolism. These data led to a hypothesis for a central role for altered cellular ion homeostasis in mediating the clinical linkage of cardiovascular and metabolic disease. According to this ionic hypothesis, essential hypertension, non-insulin dependent diabetes, and their frequently associated features of obesity, left ventricular hypertrophy, and accelerated atherosclerosis all derive from and reflect different clinical manifestations of the same underlying cellular lesion, characterized at least in part by elevated cytosolic free calcium and suppressed free magnesium levels.