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 contraction of endothelium-denuded porcine pulmonary arteries was investigated. 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 mumol/L) reduced the maximum of contraction without significantly affecting the thrombin-induced increase in IP3. To evaluate the role of PKC for the contractile response, the PKC was activated directly by phorbol 12,13-dibutyrate (PDBu, 50 nmol/L). The phorbol ester produced a slowly increasing tonic contraction without any changes in the basal IP3 level. There was a moderate inhibition of PDBu-induced contractions in Ca(2+)-free solution, while they were not inhibited after preincubation with verapamil. Preincubation with the PKC inhibitor staurosporine (50 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 and the phasic component of contraction were still evident. These results suggest that IP3 and PKC are involved in the thrombin-induced contraction. The phasic component of contraction is associated with the generation of IP3; the tonic component might be due to the activation of PKC.