ENDOTHELIN-1 INDUCED SUSTAINED CONTRACTIONS OF TRACHEAL SMOOTH-MUSCLEINVOLVE AN ACTIVATION OF PROTEIN-KINASE-C

Endothelin-1, a potent vasoconstrictor peptide produces concentration dependent contractions in lamb tracheal smooth muscle. These contracti ons are not inhibited by low doses (up to 20 mu M) of trifluoroperazin e and W-7, the calmodulin/myosin light chain kinase (MLCK) inhibitors. At higher concentrations (200 mu M), a delayed and poor reversal of i sometric tensions results. These relaxations are coupled with a partia l dephosphorylation of regulatory myosin light chain (MLC). Preincubat ion of fiber strips in MLCK inhibitors (200 mu M) results in a delayed and attenuated contractile response but without a dephosphorylation o f MLC. H-7, a putative protein kinase C antagonist (25-100 mu M) aboli shes endothelin-1 induced contractile effects rapidly (50% relaxation within 1-3 min). Moreover, such relaxations are accompanied by complet e dephosphorylation of MLC. Phorbol 12, 13-dibutyrate, an exogenous ac tivator of protein kinase C potentiates the endothelin induced contrac tions. Inactive phorbol ester, 4 alpha-phorbol ester does not elicit a ny contractile response in the muscle. The down regulation of protein kinase C, on the other hand suppresses such potentiated contractile re sponses. These results suggest that endothelin-1 induced contractile t ensions in tracheal smooth muscle are mediated by a mechanism that inv olves an activation of enzyme protein kinase C.