1. The effects of plasma fractions from essential hypertensive subjects (n = 14) and normotensive subjects (n = 14) on Ca2+ transport in permeabilized human neutrophils was studied using an ion-selective electrode.
2. Plasma fractions were obtained by gel filtration and contained substances with a molecular mass in the range 1000–1500 daltons. This fraction isolated from essential hypertensive subjects has been shown to increase blood pressure after intravenous injection in the rat.
3. The rate of Ca2+ uptake by permeabilized neutrophils after addition of extracellular Ca2+ was significantly accelerated during incubation of the cells with the hypertensive fraction (1049.3 ±807.7% vs 242.5 ±320.9% of the control value, mean ± sd, P < 0.05).
4. It is concluded that the hypertensive plasma fraction increases Ca2+ accumulation in subcellular particles, so that under excitatory conditions Ca2+ release in arterial smooth muscle might be enhanced.