Human platelet calcium measurements methodological considerations and comparisons with calcium mobilization in vascular smooth muscle cells

Platelets are used as models for vascular smooth muscle cells (VSMC) in evaluating intracellular cal­cium ([Ca2+]j) metabolism in humans. This study was designed to determine if agonist-induced in­creases in [Ca2+]i in platelets occur via release from intracellular stores as previously demonstrated for VSMC. Incubation of purified platelets loaded with fura-2-AM in media containing 1.5 mmol/L Ca2+ resulted in higher basal [Ca2+]j than platelets incu­bated in Ca2+-free media. In addition, vasopressin-induced platelet [Ca2+]i transients were almost com­pletely blocked by Ca2+ channel blockers. Thus, in contrast to VSMC, the transmembranous flux of ex­tracellular Ca2+ is the major mechanism in vaso­pressin-induced increases in platelet [Ca2+]i, while mobilization of intracellular Ca2+ stores is only minimally involved. Am J Hypertens 1991;4:546-549.