ERYTHROCYTE CA2+ HANDLING IN THE SPONTANEOUSLY HYPERTENSIVE RAT, EFFECT OF VANADATE IONS

Cytosolic Ca2+ concentration ([Ca2+]i) and Ca-45(2+) influx were investigated in erythrocytes from conscious spontaneously hypertensive rats (SHR) and their normotensive controls Wistar-Kyoto (WKY). [Ca2+]i was evaluated with fura-2 and intra- and extra-cellular calibration parameters were compared. Irrespective of the calibration parameters used, erythrocyte [Ca2+]i was always significantly higher in SHR than in WKY and Wistar rats (by 25 and 40%, p<0.01 and 0.001). A rise of the external Ca2+ concentration from 1 to 2 mmol/l increased less [Ca2+]i in SHR than in WKY erythrocytes (17 vs 37%, p<0.01). SHR erythrocytes incorporated more Ca-45(2+) than hose from WKY, with an initial rate of Ca-45(2+) uptake higher by 57% than that of WKY erythrocytes (p<0.05). Vanadate ions, after corrections of their quenching effect on red cell and fura-2 fluorescence signals, increased [Ca2+]i by 19% in WKY erythrocytes (p=0.05), but did not modify the SHR values. They also increased Ca-45(2+) accumulation and the initial rate of Ca-45(2+) influx in WKY erythrocytes only (p<0.01). This study indicates that, when compared to WKY rats, erythrocytes from SHR arc characterized by higher [Ca2+]i values, higher initial rate of Ca2+ influx and low sensitivity to vanadate ions.