ABSTRACT
BACKGROUND: It is well established that vascular contraction is caused by not only an increase in cytosolic Ca2+ level but also activations of Ca2+-sensitizing mechanisms including protein kinase C (PKC) and low molecular GTP binding protein. However, the roles of PKC and RhoA, a low molecular GTP-binding protein, on the receptor agonist-mediated contraction in swine pulmonary artery has not been clarified. In the present study, we examined the contribution of PKC isoform and RhoA to the arterial stimulants-induced contraction in swine pulmonary artery. METHOD: The large (> 5 mm), medium (1-3 mm) and small (< 1 mm in outer diameter) sized pulmonary arteries were excised and the contractions were recorded isometrically. The contents and subcellular distribution of PKC isoforms and RhoA were detected using immunoblotting. RESULTS: In medium pulmonary artery, norepinephrine (NE, 10 nM-30micrometer) led contraction in a dose-dependent manner. In large and small pulmonary arteries, however, NE failed to induce a contraction. Adding of 12-deoxyphorbol 13-isobutyrate (DPB, 1micrometer), a PKC activator, developed muscle force in 1 mM EGTA-contained Ca2+-free physiological salt solution. The expressions of PKC alpha, elsilon were significantly increased in medium pulmonary artery. NE (10micrometer) evoked the translocation of RhoA from cytosol to the membrane but not those of PKC isoforms. In Ca2+-free physiological salt solution, DPB (1micrometer) caused a translocation of PKC isoforms. CONCLUSIONS: These results support that NE induces contraction via RhoA pathway but not PKC pathway in swine pulmonary artery.