Involvement of inositol 1,4,5-triphosphate and protein kinase C in thrombin-induced contraction of porcine pulmonary artery

Abstract

The role of the intracellular messengers inositol 1,4,5-triphosphate (IP 3) 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 IP 3 to about 160% of the unstimulated control. Omission of extracellular Ca 2+ or preincubation with verapamil (10 μmol/L) reduced the maximum of contraction without significantly affecting the thrombin-induced increase in IP 3. 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 IP 3 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 IP 3 and the phasic component of contraction were still evident. These results suggest that IP 3 and PKC are involved in the thrombin-induced contraction. The phasic component of contraction is associated with the generation of IP 3; the tonic component might be due to the activation of PKC.