ROLE OF PROTEIN-KINASE-C IN NONSENSITIZED AND PASSIVELY SENSITIZED HUMAN ISOLATED BRONCHIAL SMOOTH-MUSCLE

To examine the role of protein kinase C (PKC) activation in the contro l of the mechanical activity of human isolated bronchial smooth muscle obtained at thoracotomy, the effect of the phorbol ester phorbol 12,1 3-dibutyrate (PDB) was evaluated. PDB produced slowly developing and s ustained contractions that were reduced 1) by the PKC inhibitor stauro sporine and 2) after long-term (12 h) exposure to PDB, which downregul ates PKC. Moreover, the inactive phorbol ester 4 alpha-phorbol 12,13 d idecanoate had no contractile effect. Removal of external Ca2+ or addi tion of the Ca2+ -channel antagonist verapamil reduced the PDB-induced contraction. Passive sensitization of human isolated bronchial rings, i.e., incubation overnight of tissues in serum from atopic asthmatic patients, decreased the maximal response to PDB to 28.9 +/- 8% of the maximal response to acetylcholine (ACh) when compared with that of pai red nonsensitized rings, i.e., tissues incubated overnight in serum fr om normal subjects (46.7 +/- 9.4% of the maximal response to ACh, n = 5, P < 0.05). The decrease in the response to PDB induced by either lo ng-term preexposure to PDB or passive sensitization was reversed when both types of tissues were allowed to recover unstimulated for 3 h bef ore PDB application. These results show that 1) PKC activation induces maintained contractions in human isolated airway smooth muscle that a re largely dependent on extracellular calcium; 2) passive sensitizatio n alters the PKC-mediated response in a way similar to that induced by prolonged stimulation of PKC.