Kinetic characteristics of thrombin receptor-mediated responses in rat megakaryocytes

Kinetic characteristics of thrombin receptor-mediated responses on rat megakaryocytes were examined by the use of the perforated patch clamp combined with the rapid drug exchange system termed the 'Y-tube method'. The application of thrombin evoked repetitive Ca2+-activated K+ current (I-KCa) in a concentration-dependent manner. The characteristic features for thrombin-induced response compared with purinoceptor-induced response were the long latency, long washout time and fast desensitization. The similar I-KCa as thrombin was induced by trypsin. Thrombin- and trypsin-induced I-KCa were both inhibited by the protease inhibitor, SBTI, and the washout time for thrombin was markedly shortened (7.4 +/- 2.2 s) when thrombin was washed out by a solution containing soybean trypsin inhibitor. A synthetic thrombin receptor agonist peptide induced I-KCa oscillation with shorter latency than thrombin.