ANALYSIS OF MECHANISM OF LOCAL-ANESTHETIC INHIBITION OF PLATELET-AGGREGATION AND SECRETION

Abstract

Aggregation induced in human platelets by thrombin (TH), collagen [from bovine achilles tendon] (COLL) or the Ca2+ ionophore, A23187 [2-[3.beta.,9.alpha.,11.beta.-trimethyl)-8-(2-pyrrolecarboxymethyl)-1,7-dioxaspiro[6,6]undecyl-2.beta.-methyl]-5-methylaminobezoxazole-4-carboxylic acid], was blocked by dibucaine and tetracaine. COLL-induced aggregation was blocked at lower concentrations of anesthetics (0.01-0.5 mM) than TH- or A23187-induced aggregation (0.2-2.0 mM). The rate and magnitude of the release of ADP, Ca2+ and serotonin was decreased by anesthetics. Secretion due to COLL, but not to TH, required extracellular Ca2+ and was accompanied by increased 45Ca uptake which was inhibited by local anesthetics. A23187-induced secretion was partially dependent upon external Ca2+ and was accompanied by increased 45Ca uptake. Anesthetics increased 45Ca uptake when added before, but not after, A23187. This effect can be explained by postulating that the anesthetics prevent the release of an internal pool of Ca2+, thereby affecting the Ca2+ gradient between platelet cytoplasm and extracellular fluid. Platelets degranulated, but not aggregated, by exposure to TH in the presence of ethylene glycol bis(.beta.-aminoethyl ether)-N,N''-tetraacetic acid and human plasmin were isolated by Sepharose gel filtration. Such platelets did not aggregate with COLL or TH, but did aggregate with A23187, an effect blocked by local anesthetics. Platelet aggregation and secretion are independent Ca2+-requiring processes, each of which is inhibitable by local anesthetics, presumably by blocking Ca2+ influx or the mobilization of intracellular Ca2+ stores.