Eight aged (70.1 +/- 2.1 years), nonobese (body mass index [BMI] = 26.3 +/- 0.4), hypertensive (systolic blood pressure [SBP] = 184 +/- 4.1; diastolic blood pressure [DBP] = 105 +/- 2.4 mm Hg) subjects underwent a euglycemic hyperinsulinemic (7.1 pmol/kg x min during 240 min) glucose clamp with four different infusions: a) 0.9% NaCl; b) 1.0 micrograms/kg x min nifedipine; c) 100 mumol/min magnesium; d) 1.0 micrograms/kg x min nifedipine plus 100 mumol/min magnesium. All tests were performed in random order. Simultaneous D-3-H glucose infusion and indirect calorimetry allowed us to determine glucose turnover parameters and substrate oxidation. Insulin infusion per se stimulated erythrocyte magnesium (1.83 +/- 0.04 v 1.98 +/- 0.03 mmol/L, P < .03) and calcium (4.7 +/- 0.3 v 6.2 +/- 0.4 mumol/L, P < .02) accumulation, and enhanced total body glucose disposal oxidative and nonoxidative glucose metabolisms. Infusion of insulin and nifedipine v insulin alone reduced insulin-mediated increase in intracellular calcium (5.4 +/- 0.3 v 6.2 +/- 0.4 mumol/L, P < .02), but potentiated the insulin effect upon nonoxidative glucose (15.4 +/- 0.4 v 11.1 +/- 0.3 mumol/kg lean body mass [LBM] x min, P < .03) metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)