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.
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.
Poiraudeau
S
S
Institut National de la Santé et de la Recherche Médicale, Université Paris, V, Groupe Hospitalier Necker-Enfants, Malades, Paris, France.
Lieberherr
M
M
Kergosie
N
N
Corvol
M T
MT
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D002356:Cartilage / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002460:Cell Line; D002772:Cholera Toxin / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D005163:Factor Analysis, Statistical; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology; D009355:Neomycin / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D011817:Rabbits; D017526:Receptor, IGF Type 1 / Q000502:physiology*; D017527:Receptor, IGF Type 2 / Q000502:physiology*
D015220:Calcium Channels; D004963:Estrenes; D007328:Insulin; D011760:Pyrrolidinones; D017527:Receptor, IGF Type 2; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D002772:Cholera Toxin; D017526:Receptor, IGF Type 1; D009355:Neomycin; D002118:Calcium