Effect of Carvedilol on Ca2+ Movement and Cytotoxicity in Human MG63 Osteosarcoma Cells

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Abstract
Carvedilol is a useful cardiovascular drug for treating heart failure, however, the in vitro effect on many cell types is unclear. In human MG63 osteosarcoma cells, the effect of carvedilol on intracellular Ca2+ concentrations ([Ca2+]i) and cytotoxicity was explored by using fura‐2 and tetrazolium, respectively. Carvedilol at concentrations greater than 1 μM caused a rapid rise in [Ca2+]i in a concentration‐dependent manner (EC50=15 μM). Carvedilol‐induced [Ca2+]i rise was reduced by 60% by removal of extracellular Ca2+. Carvedilol‐induced Mn2+‐associated quench of intracellular fura‐2 fluorescence also suggests that carvedilol induced extracellular Ca2+ influx. In Ca2+‐free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+‐ATPase, caused a monophasic [Ca2+]i rise, after which the increasing effect of carvedilol on [Ca2+]i was inhibited by 50%. Conversely, pretreatment with carvedilol to deplete intracellular Ca2+ stores totally prevented thapsigargin from releasing more Ca2+. U73122, an inhibitor of phospholipase C, abolished histamine (an inositol 1,4,5‐trisphosphate‐dependent Ca2+ mobilizer)‐induced, but not carvedilol‐induced, [Ca2+]i rise. Pretreatment with phorbol 12‐myristate 13‐acetate and forskolin to activate protein kinase C and adenylate cyclase, respectively, did not alter carvedilol‐induced [Ca2+]i rise. Separately, overnight treatment with 0.1–30 μM carvedilol inhibited cell proliferation in a concentration‐dependent manner. These findings suggest that in human MG63 osteosarcoma cells, carvedilol increases [Ca2+]i by stimulating extracellular Ca2+ influx and also by causing intracellular Ca2+ release from the endoplasmic reticulum and other stores via a phospholipase C‐independent manner. Carvedilol may be cytotoxic to osteoblasts.