Sustained increase of extracellular calcium concentration causes arterial vasoconstriction in humans

Background Vascular tone is affected by extracellular electrolytes. Objective To evaluate whether a sustained increase in the extracellular calcium concentration may produce vasoconstriction in humans. Design Cross-sectional data of a cohort study of 65 patients with end-stage renal failure. Measurements Arterial tone was obtained from radial artery waveforms. Intracellular stored calcium and sarcoendoplasmic reticulum Ca 2+ -ATPase activity were measured in mononuclear leukocytes using fluorescent dye techniques and oxalate-supported calcium uptake. Results During the haemodialysis sessions the extracellular calcium concentration increased significantly from 2.28 ± 0.03 to 2.63 ± 0.03 mmol/l (n = 65; mean ± SEM; P< 0.001) and arterial tone increased from 31 ± 2 to 44 ± 3 mmHg/ml (n = 65; P< 0.001). Multivariate analysis showed that pre and postdialysis extracellular calcium and pre and postdialysis body weight were the only independent predictors of arterial tone during haemodialysis. Intracellular stored calcium in mononuclear leukocytes significantly declined from 5.1 ± 1.2 arbitrary units at the start to 2.3 ± 0.6 arbitrary units at the end of haemodialysis (n = 10; P= 0.01). The activity of the sarcoendoplasmic reticulum Ca 2+ -ATPase significantly decreased from 13.6 ± 2.6 nmol calcium/mg protein per 5 min at the start to 9.2 ± 1.6 nmol calcium/mg protein per 5 min at the end of haemodialysis (n = 28; P = 0.01). On the other hand, when a low dialysate calcium concentration was used, the increase in artery tone and reduction in sarcoendoplasmic reticulum Ca 2+ -ATPase activity were reversed. Conclusion A sustained increase in the extracellular calcium concentration causes arterial vasoconstriction in humans. In addition, a reduction of sarcoendoplasmic reticulum Ca 2+ -ATPase activity and intracellular stored calcium in mononuclear leukocytes was observed.