Different mechanisms are involved in intracellular calcium increase by insulin-like growth factors 1 and 2 in articular chondrocytes: Voltage-gated calcium channels, and/or phospholipase C coupled to a pertussis-sensitive G-protein

Abstract

This study describes the mechanisms involved in the IGF-1 and IGF-2-induced increases in intracellular calcium concentration [Ca2+]i in cultured chondrocytes and the involvement of type 1 IGF receptors. It shows that IGF-1, IGF-2, and insulin increased the cytosolic free calcium concentration [Ca2+]i in a dose-dependent manner, with a plateau from 25 to 100 ng/ml for both IGF-1 and IGF-2 and from 1 to 2 micrograms/ml for insulin. The effect of IGF-1 was twice as great as the one of IGF-2, and the effect of insulin was 40% lower than IGF-1 effect. Two different mechanisms are involved in the intracellular [Ca2+]i increase. 1) IGF-1 and insulin but not IGF-2 involved a Ca2+ influx through voltage-gated calcium channels: pretreatment of the cells by EGTA and verapamil diminished the IGF-1 or insulin-induced [Ca2+]i but did not block the effect of IGF-2. 2) IGF-1, IGF-2, and insulin also induced a Ca2+ mobilization from the endoplasmic reticulum: phospholipase C (PLC) inhibitors, neomycin, or U-73122 partially blocked the intracellular [Ca2+]i increase induced by IGF-1 and insulin and totally inhibited the effect of IGF-2. This Ca2+ mobilization was pertussis toxin (PTX) dependent, suggesting an activation of a PLC coupled to a PTX-sensitive G-protein. Lastly, preincubation of the cells with IGF1 receptor antibodies diminished the IGF-1-induced Ca2+ spike and totally abolished the Ca2+ influx, but did not modify the effect of IGF-2. These results suggest that IGF-1 action on Ca2+ influx involves the IGF1 receptor, while part of IGF-1 and all of IGF-2 Ca2+ mobilization do not implicate this receptor.

Specific Activation of Insulin-like Growth Factor-1 Receptor by Ginsenoside Rg5 Promotes Angiogenesis and Vasorelaxation

“…Moreover, Rg5 promoted Ca 2ϩ -dependent eNOS dimerization and NO production, which were mediated by the G i -mediated PLC pathway. These data are consistent with previous results in which IGF-1R activated G i -mediated PLC activation and Ca 2ϩ mobilization (27,28). Inhibitors of these signal mediators suppressed Rg5-mediated FAK activation and angiogenesis, suggesting that G i protein-mediated elevation of [Ca 2ϩ ] i is responsible for FAK phosphorylation (35).…”

“…5A). Activation of the G i protein complex stimulates PLC activation and Ca 2ϩ mobilization, resulting in promotion of cell growth and migration (27,28). We next examined whether Rg5 regulates the G i protein-mediated PLC/Ca 2ϩ pathway.…”

Voltage-Dependent Calcium Channels in Chondrocytes: Roles in Health and Disease

“…Furthermore, in high-density primary cultures of human articular chondrocytes, application of verapamil or nifedipine abrogated the stimulatory effect of prostaglandin E2 (PGE2) on IGFBP-3, a protein that regulates the bioactivity and bioavailability of insulin-like growth factor-1 (IGF-1), an important mediator of chondrocyte metabolism [25]. In a followup study, IGF-1, IGF-2 and insulin all increased cytosolic Ca 2+ levels in cultured rabbit articular chondrocytes but through different mechanisms; Ca 2+ influx mediated by L-type VDCCs was involved downstream of IGF-1 and insulin, since verapamil diminished these responses [26].…”

Human growth hormone and insulin-like growth factor-I inhibit erythropoietin secretion from the kidneys of adult rats

“…An increase in intracellular calcium can be achieved by an influx of Ca 2+ through voltage-dependent Ca 2+ channels located in the plasma membrane or by mobilization of Ca 2+ from intracellular stores (Cruzalegui & Bading 2000). IGF-I also increases intracellular Ca 2+ (Kojima et al 1988, Poiraudeau et al 1997). An increase in the intracellular calcium concentration decreased EPO secretion.…”