Protein kinase C induced changes in human airway smooth muscle tone: the effects of Ca2+ and Na+ transport.

Activation of protein kinase C by phorbol 12,13-dibutyrate (PDB) (1 nM-3 μM) caused a concentration-dependent contractile response in human isolated bronchus. The mean maximal contraction was 26 ± 4.4% (n = 11) of that induced by acetylcholine (1 mM). The contraction was increased by the presence of the Ca2+ ionophore (A23187) to 47 ± 6% (n = 7, P 0.05). The Ca2+ channel antagonist, verapamil (1 μM) significantly reduced the contraction from 32.3 ± 4.9 to 12.5 ± 1% (n = 4, P < 0.05) and in the presence of nifedipine (1 μM), the contractile response was abolished. A single concentration of 10 μM PDB produced a biphasic response-relaxation (6 ± 1%) followed by contraction (76 ± 4%, n = 4) which was greater than that produced when responses were obtained cumulatively. The relaxation response was inhibited by the addition of a Na+K+ exchange antagonist, ouabain (10 μM) which also markedly potentiated the contractile response to 110 ± 10% (n = 4, P < 0.05). These results suggest that the protein kinase C-mediated contraction in human airway smooth muscle is dependent on extracellular Ca2+ influx. Protein kinase C may also phosphorylate Na+K+-ATPase resulting in a relaxation response.