Increased cytosolic free calcium in red blood cells is associated with essential hypertension in humans.

Intracellular free calcium (Cai2+) was measured in human red blood cells (RBCs) using the Ca(2+)-sensitive fluorescent probe, fluo-3. Fresh RBCs were loaded with the acetoxymethyl ester of fluo-3 (fluo-3-AM) in vitro. Following incubation at 37 degrees C for 60 min, cells were separated from nonincorporated fluo-3-AM and fluo-3. Fluorescence was quantified with excitation and emission wavelengths of 506 nm and 526 nm, respectively. The relatively long wavelength characteristics of fluo-3 avoid much of the interference from hemoglobin that makes agents such as quin-2 and fura-2 of limited value in RBCs. A protocol with corrections for quenching and for extracellular fluo-3 was employed for each sample. Cai2+ in red blood cells from 15 normotensive volunteers averaged 134 +/- 12 nmol/L. In RBCs from 30 hypertensive patients who were not treated pharmacologically, Cai2+ was 317 +/- 32 nmol/L (P < .05). In a group of 27 hypertensives who were treated with various drugs, RBC Cai2+ was 221 +/- 27 nmol/L. Measurements were also performed in RBCs from 16 patients before and at least 2 weeks following treatment with one or more antihypertensive agents. Reduction of RBC Cai2+ from 342 +/- 47 to 252 +/- 39 (P < .001) was observed in 16 patients whose blood pressure fell with treatment. Overall, there was a correlation between RBC Cai2+ and diastolic blood pressure (r = 0.413, P < .01, d.f. = 71). Thus, the present results confirm an association between elevated RBC Ca2+ and essential hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)