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  • Title: Oscillation of cytoplasmic free calcium concentration induced by insulin-like growth factor I.
    Author: Kojima I, Mogami H, Ogata E.
    Journal: Am J Physiol; 1992 Mar; 262(3 Pt 1):E307-11. PubMed ID: 1550224.
    Abstract:
    The effect of insulin-like growth factor I (IGF-I) on cytoplasmic free calcium concentration ([Ca2+]c) was studied in single BALB/c 3T3 cells by monitoring fura-2 fluorescence. In primed competent cells, IGF-I (1 nM) increased [Ca2+]c in approximately 60% of the cells tested. IGF-I-mediated elevation of [Ca2+]c was observed after a 4- to 17-min lag period. Elevation of [Ca2+]c was only transient but was followed by repetitive increases in [Ca2+]c. The interval between each peak was quite constant in each cell at a given concentration of IGF-I. When the concentration of IGF-I was reduced, both the latent period and interval of each peak were prolonged, whereas amplitude of the increase in [Ca2+]c was not altered. In medium containing 10 microM extracellular calcium, IGF-I did not cause any increase in [Ca2+]c. Likewise, blockade of IGF-induced calcium entry by either cobalt or tetramethrin abolished IGF-I action on [Ca2+]c. IGF-I-mediated oscillation was not affected by either ryanodine or caffeine, compounds that affect calcium-induced calcium release. In addition, pretreatment of the cell with neomycin did not affect IGF-I-mediated oscillation. In agreement with this, IGF-I did not augment production of [3H]inositol trisphosphate in cells prelabeled with [3H]inositol. These results indicate that IGF-I induces oscillation of [Ca2+]c in a single primed competent cell and that the oscillation is totally dependent on IGF-I-mediated calcium entry.
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