DIFFERENCES IN SENSITIVITY TO THE SPECIFIC PROTEIN-KINASE-C INHIBITOR RO31-8220 BETWEEN SMALL AND LARGE BRONCHIOLES OF THE RAT

1 The involvement of protein kinase C (PKC) in constriction of small bronchioles has never been investigated. In this study we have examined the effects of the specific PKC inhibitors Ro31-8220 and Ro31-7549 and the non-specific inhibitor H7 on carbachol-, 5-hydroxytryptamine (5-HT)- and 4 beta-phorbol dibutyrate (4 beta-PDBu)-induced contractions in large and small bronchioles. 2 The study was performed on isolated bronchioles of the rat with internal diameters of 574 mu m +/- 11 (small, n = 128), and 1475 mu m +/- 32 (large, n = 93), using a Mulvaney-Halpen small vessel myograph. 3 In these preparations 4 beta-PDBu had no effect if added on its own. However, after precontracting with 30 mM K+, 0.5 mu M 4 beta-PDBu caused a contractile response of 110.4 +/- 7.0% T-K (T-K = maximum response to 75 mM K+ in small and 69.3 +/- 6.5% T-K in large bronchioles. Ro31-8220, Ro31-7549 and H7 all showed concentration-dependent inhibition of this response. 4 In small bronchioles 10 mu M Ro31-8220 shifted both the carbachol and 5-HT concentration- response curves to the right, and reduced the maximum response. In contrast, 10 mu M Ro31-8220 had no significant effect on the EC(50) to carbachol of larger bronchioles, although the maximum response was reduced, and had no significant effect on the 5-HT concentration- response curve. 200 mu M H7. shifted the carbachol concentration- response curve to the right as well as reducing the maximal response in both small and large bronchioles. 5 Large bronchioles exhibited a greater rate of decay of carbachol-induced contraction than did small bronchioles. Pretreatment with Ro31-8220 accelerated the rate of decay. 6 Pretreatment with 10 mu M Ro31-8220 caused a small reduction in the response to 75 mM K+ in both small and large bronchioles (small: to 87.8 +/- 3.0% T-K; large: to 94.1 +/- 0.8% T-K). H7 at 200 mu M caused a much larger reduction in both preparations (small: to 75.1 +/- 3.0% T-K); large: to 82.7 + 0.6% T-K) 7 Small bronchioles were more sensitive than larger bronchioles to agonists and phorbol ester. The protein kinase inhibitor Ro31-8220 could reduce agonist-induced constriction in small and large bronchioles, as well as reducing or abolishing phorbol ester-induced contractions. Small bronchioles were more sensitive than large bronchioles to Ro31-8220. These results suggest that there is a significant PKC involvement in constriction of bronchioles to carbachol and 5-HT, and that the proportion of the contractile response that can be attributed to PKC is greater in smaller than larger bronchioles.