Effects of aging on serum ionized and cytosolic free calcium - Relation tohypertension and diabetes

Elevated cytosolic free calcium (Ca-i) and reciprocally reduced, extracellu lar ionized calcium (Ca-ion) levels are observed in both hypertension and n on-insulin-dependent diabetes mellitus (NIDDM). Because the changes of vasc ular function and insulin sensitivity in these conditions resemble the chan ges associated with "normal" aging, we wondered to what extent similar alte rations in calcium metabolism occur with aging per se in the absence of ove rt hypertension or diabetes. We therefore measured platelet Ca, levels by s pectrofluorometry and serum Ca-ion levels in normotensive, nondiabetic, hea lthy, normal, elderly (>65 years old) subjects, mean age +/-SEM, 72.2+/-1.5 years old (n = 11); in healthy, normal, young (<65 years old) adults, 46.1 +/-2.3 years old (n = 12); in 10 young adult hypertensives, 48.6+/-1.9 year s old: and in 10 normotensive NIDDM subjects, 49.2+/-1.6 years old. Platele t Ca-i levels were higher (104.5+/-4.9 versus 80.2+/-1.8 nmol/L, P<0.01) an d Ca-ion levels lower (1.212+/-0.010 versus 1.236+/-0.011 mmol/L, P<0.05) i n normal elderly compared with young control subjects, but normal elderly C a-i and Ca-ion levels were indistinguishable from those in hypertensive (Ca -i 107.5+/-3.6 nmol/L, Ca-ion 1.210+/-0.009 mmol/L) and NIDDM (Ca-i 110.7+/ -4.7 nmol/L, Ca-ion 1.204+/-0.014 mmol/L) subjects. In normal subjects, sig nificant correlations were found between platelet Ca-i levels and age (r=0. 655, P<0.01) and between Ca-i levels and systolic blood pressure (r=0.733, P<0.001). We conclude that aging is associated with alterations of Ca-i and Ca-ion levels resembling those changes present at any age in hypertension and type 2 diabetes. We hypothesize that these alterations of calcium metab olism underlie the predisposition to the alterations of blood pressure and insulin sensitivity characteristic of "normal" aging. The data also suggest that studies of the aging process should be limited to subjects with norma l blood pressure and glucose tolerance.