Colic in horses. Pathophysiology, clinical examination and therapy
Hesselholt, M.
Nordisk Veterinaermedicin 37(4): 201-216
1985
ISSN/ISBN: 0029-1579 PMID: 4059045 Document Number: 260073
This paper reviews some of our most recent studies concerning the relationship between phospholipid metabolism and calcium mobilization in thrombin-stimulated platelets. Evidence is provided that phospholipase C activation does not require any increase in cytoplasmic calcium but is subsequent to a yet unknown membrane modification rendering the substrate accessible to the enzyme upon thrombin-receptor binding. In contrast, the much higher calcium dependence of phospholipase A2 led us to conclude that cytoplasmic free calcium might increase to in excess of 1.6 microM even in the absence of external calcium. This is supported by our estimation that calcium is present in dense tubular system in rather large excess, as measured on purified vesicles derived from this organelle. We thus suggest that the level of inositol-1,4,5-tris-phosphate is rate limiting in the process of calcium mobilization which implies that calcium influx through the plasma membrane might become a critical event with weak agonist poorly activating phospholipase C.