INVOLVEMENT OF INOSITOL 1,4,5-TRIPHOSPHATE AND PROTEIN-KINASE-C IN THROMBIN-INDUCED CONTRACTION OF PORCINE PULMONARY-ARTERY

The role of the intracellular messengers inositol 1,4,5-triphosphate ( IP3) and protein kinase C (PKC) in the thrombin (3 U/mL)-induced contr action of endothelium-denuded porcine pulmonary arteries was investiga ted. Thrombin induced a sustained contractile response with an initial transient increase in IP3 to about 160% of the unstimulated control. Omission of extracellular Ca2+ or preincubation with verapamil (10 mu mol/L) reduced the maximum of contraction without significantly affect ing the thrombin-induced increase in IP3. To evaluate the role of PKC for the contractile response, the PKC was activated directly by phorbo l 12,13-dibutyrate (PDBu, 50 nmol/L). The phorbol ester produced a slo wly increasing tonic contraction without any changes in the basal IP3 level. There was a moderate inhibition of PDBu-induced contractions in Ca2+-free solution, while they were not inhibited after preincubation with verapamil. Preincubation with the PKC inhibitor staurosporine (5 0 nmol/L) significantly reduced the PDBu-induced contraction (by about 80%). In thrombin-stimulated vessels staurosporine only inhibited the tonic phase of the contractile response whereas the increase in IP3 a nd the phasic component of contraction were still evident. These resul ts suggest that IP3 and PKC are involved in the thrombin-induced contr action. The phasic component of contraction is associated with the gen eration of IP3; the tonic component might be due to the activation of PKC.