Potentiation by thrombin of hyposmotic glutamate and taurine efflux from cultured astrocytes: signalling chains.
Activation of protein-activated receptor (PAR-1) by thrombin potentiates the hyposmotic efflux of (3)H-D-aspartate and (3)H-taurine from cultured cerebellar astrocytes. This effect is mediated by a thrombin-elicited increase in cytosolic Ca(2+) levels [Ca(2+)](i) and the activation of phosphoinositide-3-kinase (PI3K). These signalling pathways operate independently showing additive effects if prevented simultaneously. The contribution of the Ca(2+)-mediated pathway to thrombin-increased D-aspartate or taurine efflux, evaluated by the inhibitory effect of preventing [Ca(2+)](i) rise, was higher for D-aspartate (64% efflux decrease) than for taurine (40% decrease). The PI3K blocker decreased 48% and 36% D-aspartate and taurine efflux, respectively. Hyposmolarity increases phosphorylation of EGFR and c-src, but thrombin did not enhance this effect. Blockade of EGFR/src phosphorylation marginally reduced (11-14%) the hyposmolarity plus thrombin efflux of D-aspartate; taurine efflux was more sensitive to these blockers (18-26%). Since thrombin has no effect increasing EGFR/src phosphorylation in astrocytes, the contribution of this transactivation pathway may represent the inhibition of the hyposmotic efflux solely.
Cruz-Rangel
S
S
Departamento de Biofísica, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico, DF, 04510, Mexico.
Hernández-Benítez
R
R
Vázquez-Juárez
E
E
López-Dominguez
A
A
Pasantes-Morales
H
H
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D066246:ErbB Receptors / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D009994:Osmolar Concentration; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D015398:Signal Transduction / Q000502:physiology*; D013654:Taurine / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism
D002118:Calcium; D066246:ErbB Receptors; D018698:Glutamic Acid; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D013654:Taurine; D013917:Thrombin; D019061:src-Family Kinases