Cell membrane microviscosity and Ca(2+)-Mg(2+)-ATPase activity do not contribute to hypertension in the spontaneously hypertensive rat model

1. The relationships between systolic blood pressure and altered erythrocyte Ca(2+)-Mg(2+)-ATPase activity and membrane microviscosity were assessed in membranes prepared from 20-week-old female Wistar-Kyoto normotensive and spontaneously hypertensive rats obtained from two different sources (Charles River and Harlan OLAC) and a second filial (F2) generation derived from a cross between Wistar-Kyoto rats and spontaneously hypertensive rats from one source (Charles River). 2. Spontaneously hypertensive rats from both sources had systolic blood pressures significantly higher than those of Wistar-Kyoto animals (P < 0.05; 151 +/- 4 and 110 +/- 3 mmHg, Charles River; 155 +/- 4 and 122 +/- 4 mmHg, Harlan OLAC). The systolic blood pressures for the F2 rat population ranged between 73 and 168 mmHg. 3. Ca(2+)-Mg(2+)-ATPase activity was measured as ATP-dependent 45Ca2+ uptake into inside-out vesicles and microviscosity assessed by the measurement of polarization anisotropy of membrane incorporated fluorescent probes including 1,6-diphenyl-1,3,5-hexatriene, trimethylamino-1,6-diphenyl-1,3,5-hexatriene and a series of anthroyloxy fatty acids. 4. Contrary to previous studies, no relationship between adult systolic blood pressure and erythrocyte Ca(2+)-Mg(2+)-ATPase activity or general or localized membrane microviscosity was indicated by the comparison of spontaneously hypertensive and Wistar-Kyoto animals or in the analysis of the F2 rat population. 5. These results suggest that Ca(2+)-Mg(2+)-ATPase activity and membrane microviscosity are causally unrelated to hypertension in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)