PMID: 2510999Dec 1, 1989Paper

Evidence for an inhibitory effect of protein kinase C on G-protein-mediated repetitive calcium transients in hamster eggs

The EMBO Journal
K SwannS Miyazaki

Abstract

Hamster eggs undergo repetitive increases in cytoplasmic free calcium concentration ([Ca2+]i) at fertilization or after injecting guanosine-5'-0-(3-thiotriphosphate) (GTP[S]). We report the effects of protein kinase C (PKC) agonists and antagonists on these repetitive [Ca2+]i transients as measured by their associated membrane potential hyperpolarizing responses (HRs). Iontophoretic injection of GTP[S] into unfertilized eggs caused a series of repetitive HRs that declined in amplitude with time. Continuous injection of inositol 1,4,5-trisphosphate (InsP3) also caused a series of repetitive HRs, but these HRs declined in amplitude less markedly. GTP[S]-induced HRs were inhibited by the PKC agonists phorbol 12-myristate 13-acetate (TPA) (100 nM) and 1,2-dioctanoyl-glycerol (diC8) (250 microM). Conversely the PKC inhibitor sphingosine (10 microM) enhanced the number of large HRs after GTP[S] injection. TPA or sphingosine did not alter InsP3-induced HRs. We suggest that G-protein-mediated InsP3 production causes repetitive [Ca2+]i transients but that GTP[S] injection stimulates a negative feedback loop involving PKC. Adding TPA (100 nM) before insemination caused a reduction in the frequency of HRs at fertilization, but neither TPA...Continue Reading

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