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Abnormality in sarcoplasmic reticulum-dependent arterial contraction in responses to caffeine and noradrenaline in spontaneously hypertensive rats.

We studied caffeine- and noradrenaline-induced contraction in tail arteries from 4-week-old male SHR and age- and sex-matched WKY. After the sarcoplasmic reticulum Ca2+ had been depleted by the Ca(2+)-free EGTA (0.1 mmol/l) solution, the caffeine (10 mmol/l)-induced contractions in a low-Ca2+ (0.5 mmol/l) solution were smaller in SHR than in WKY. After the sarcoplasmic reticulum had been loaded with Ca2+ in physiological Ca2+ (2.5 mmol/l) solution, caffeine- and noradrenaline (10(-5) mol/l)-induced contractions in a Ca(2+)-free EGTA solution were smaller in SHR than in WKY. The Ca2+ concentration-tension relationship in skinned arterial fibres was similar in WKY and SHR. These data suggest that the ability of the sarcoplasmic reticulum to take up Ca2+ and store Ca2+ is decreased in SHR. The decreased take up and store of Ca2+ may increase cytosolic Ca2+, which elevates arterial resistance and develops hypertension in gene hypertension.