Erythrocyte Ca2+ handling in the spontaneously hypertensive rat, effect of vanadate ions

Cytosolic Ca2+ concentration ([Ca2+]i) and 45Ca2+ 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 45Ca2+ than those from WKY, with an initial rate of 45Ca2+ 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 45Ca2+ accumulation and the initial rate of 45Ca2+ influx in WKY erythrocytes only (p < 0.01). This study indicates that, when compared to WKY rats, erythrocytes from SHR are characterized by higher [Ca2+]i values, higher initial rate of Ca2+ influx and low sensitivity to vanadate ions.