RESUMO
sn-1,2-Diacylglycerol (DAG) mass and translocation of protein kinase C alpha and beta to a membrane fraction increased approximately 7 min after insemination of Xenopus laevis eggs. The DAG mass increase of 48 pmol (from 62 to 110 pmol/cell) was greater than that for inositol 1,4,5-trisphosphate (IP3; an increase of approximately 170 fmol or approximately 280-fold smaller than the DAG increase), and DAG peaks approximately 5 min after IP3. Choline mass (a measure of phosphatidyl choline-specific phospholipase D) also peaked before DAG and the choline increase (134 pmol/cell) was greater than that of DAG. There was no detectable change in phosphocholine mass (a measure of phosphatidylcholine-specific phospholipase C). During first cleavage, DAG decreased, PKC translocation was low, and choline increased and peaked (whereas published work shows an increase in IP3 mass). Artificial elevation of intracellular calcium ([Ca2+]i) increased DAG levels but prevention of the [Ca2+]i increase after fertilization did not block DAG production. Thus, sperm stimulate production of DAG and choline through [Ca2+]i-independent and [Ca2+]i-dependent paths.
Assuntos
Colina/metabolismo , Diglicerídeos/metabolismo , Fertilização/fisiologia , Xenopus laevis/fisiologia , Animais , Transporte Biológico , Cálcio/metabolismo , Membrana Celular , Embrião não Mamífero/metabolismo , Feminino , Inositol 1,4,5-Trifosfato/metabolismo , Inseminação , Ionomicina/farmacologia , Masculino , Óvulo/metabolismo , Fosforilcolina/metabolismo , Proteína Quinase C/metabolismo , Espermatozoides/metabolismo , Fatores de Tempo , ZigotoRESUMO
Our prior work suggested that the antidiabetic metformin must enter the cell to act and that the drug stimulates tyrosine kinase activity. We now report that therapeutic concentrations (approximately 1 microg/mL) of metformin stimulated the tyrosine kinase activity of the intracellular portion of the beta-subunit of the human insulin receptor (IPbetaIRK), the intracellular portion of the epidermal growth factor receptor and pp60-src, but not cAMP-dependent protein kinase. A derivative of metformin unable to lower glucose was ineffective in stimulating IPbetaIRK. Two derivatives more effective than metformin in patients were also more effective than metformin in stimulating IPbetaIRK. Higher levels (10-100 microg/mL) of metformin or methylglyoxyl bis(guanylhydrazone) inhibited the tyrosine kinases, and this inhibition may be responsible for the ability of these two drugs to block cell proliferation.