Role of extracellular calcium influx in EGF-induced osteoblastic cell proliferation

This study investigated the effects of epidermal growth factor (EGF) on cytosolic calcium ([Ca⁺⁺]_i) levels in rat calvarial osteoblasts, the nature of the regulation of this event, and the role these EGF-induced [Ca⁺⁺]_i changes have in osteoblastic cell proliferation. EGF significantly increased [Ca⁺⁺]_i measured in fura-2-loaded, individual cells. This increase was related to extracellular calcium influx. Activation of protein kinase C(PKC) by pretreating the cells with phorbol esters blocked the EGF-induced increase in [Ca⁺⁺]_i. EGF failed to increase inositol trisphosphate levels measured by high performance liquid chromatographic analysis. However, it did increase inositol bisphosphate and inositol tetrakisphosphate production. The EGF-dependent increase in DNA synthesis was partially blocked by the addition of calcium channel blockers. Therefore, it appears that the mechanism of action of EGF-induced osteoblastic cell proliferation is mediated by changes in [Ca⁺⁺]_i primarily due to extracellular calcium influx.