Receptor-Induced Diacylglycerol Formation in Permeabilized Platelets; Possible Role for a Gtp-Binding Protein
| Autor: | Richard J. Haslam, Monica M. L. Davidson |
|---|---|
| Rok vydání: | 1984 |
| Předmět: |
Blood Platelets
Serotonin G protein Receptors Cell Surface Stimulation In Vitro Techniques Guanosine Diphosphate Glycerides Diglycerides Thrombin Myosin medicine Humans Platelet Phosphorylation Receptor Diacylglycerol kinase Pharmacology Guanylyl Imidodiphosphate Chemistry Membrane Proteins Thionucleotides Biochemistry Guanosine 5'-O-(3-Thiotriphosphate) Biophysics Calcium Guanosine Triphosphate medicine.drug |
| Zdroj: | Journal of Receptor Research. 4:605-629 |
| ISSN: | 0197-5110 |
| DOI: | 10.3109/10799898409042576 |
| Popis: | Exposure of human platelets to 10 discharges from a 4.5 microF capacitor charged at 3 kV permitted isolation of a stable preparation of permeabilized platelets that, after equilibration with Ca2+ buffers (pCa less than 6) for 15 min at O degrees C, secreted 5-hydroxytryptamine (5-HT) at 25 degrees C. Thrombin enhanced the sensitivity to Ca2+ of the secretion of 5-HT by about 10-fold, whereas Arg -vasopressin and the prostaglandin endoperoxide analogue, U-46619, increased sensitivity to Ca2+ by 3 to 4-fold. This action of thrombin was associated with stimulation of diacylglycerol formation, a marked increase in phosphorylation of protein P47 and a smaller increase in phosphorylation of the P-light chain of myosin. Thrombin exerted these effects at a [Ca2+ free] of 0.1 microM, suggesting that the receptor-activated breakdown of platelet phosphoinositides to diacylglycerol may not require prior Ca2+ mobilization in intact platelets. In both the presence and absence of thrombin, a higher [Ca2+ free] was required for optimal secretion than for maximal phosphorylation of P47 and myosin light-chain, indicating that Ca2+ and possibly diacylglycerol have roles in the secretory mechanism additional to activation of the enzymes that phosphorylate these proteins. Stable GTP analogues such as guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S), and to a lesser extent GTP itself, enhanced the Ca2+ sensitivity of the secretion of 5-HT from permeabilized platelets. Moreover, GTP potentiated the stimulatory action of thrombin. These effects of GTP gamma S and GTP were associated with increased diacylglycerol formation and were inhibited by guanosine-5'-O-(2-thiodiphosphate) (GDP beta S) suggesting that a GTP-binding protein may play a role in the receptor-activated breakdown of phosphoinositides. However, as GDP beta S did not inhibit the potentiation of secretion caused by thrombin alone, a GTP-independent pathway of platelet activation may also exist. |
| Databáze: | OpenAIRE |
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