Effect of Inhibition of Na, K-ATPase on Cytosolic Free Sodium and Calcium in Platelets of Spontaneously Hypertensive Rats

Cytosolic free sodium concentrations ([Na+]i) in intact platelets of 18 spontaneously hypertensive rats (SHR) and of 18 age-matched normotensive Wistar-Kyoto rats (WKY) were measured using the sodiumsensitive fluorescent dye sodium-binding-benzofuran-isophthalate. In resting platelets [Na+]i tended to be higher in SHR compared to WKY (20.5 ± 3.5 mmol/L ν 15.1 ± 1.9 mmol/L, mean ± SEM), but the differences were not statistically significant. Stimulation of the Na-H-exchange by 1.0 U/mL thrombin increased [Na+]i in SHR by 22.9 ± 4.3 mmol/L and in WKY by 35.0 ± 5.6 mmol/L in a similar way. After inhibition of Na, K-ATPase by 1 mmol/L ouabain there was a significant rise of [Na+]i both in platelets of SHR to 38.0 ± 5.1 mmol/L (P < .01 compared to resting platelets) and in platelets of WKY to 26.5 ± 4.3 mmol/L (P < .01). However, no significant difference could be observed between these two groups. Using the calcium-sensitive dye fura-2, resting cytosolic free calcium concentrations ([Ca2+]i) were found to be significantly higher in platelets of SHR compared to WKY (171.9 ± 21.5 nmol/L ν 93.14 ± 19.7 nmol/L, P < .05). After the addition of ouabain [Ca2 + ] t was significantly higher in SHR compared to WKY (245.5 ± 32.6 nmol/L ν 159.6 ± 22.5 nmol/L, P < .05). The results do not support the hypothesis that altered sodium-calcium exchange causes elevated cytosolic free calcium in SHR. Am J Hypertens 1992;5:740–743