Mechanism of protein kinase c potentiation of airway β-adrenergic relaxation

Abstract

To evaluate the regulatory action of protein kinase C (PKC) on airway β-adrenergic function, the relaxant effects of isoproterenol (ISO) and 8 bromo-cyclic AMP (BrcAMP) were examined in tracheal smooth muscle (TSM) segments half-maximally contracted with acetylcholine in the absence (control) and presence of PKC activation with the phorbol ester, 12-deoxyphorbol 13-isobutyrate (DPS). Relative to control tissues, TSM treated with 0.1μM DPB depicted significantly enhanced maximal relaxation and sensitivity to ISO but not to BrcAMP. The enhancing effect of DPB on ISO responsiveness was completely inhibited in the presence of the PKC antagonist H-7. Inhibition of the Na+-K+ pump with either ouabain or K+-free buffer diminished the TSM relaxant response to ISO but not to BrcAMP. Inhibition of the Na+-K+ pump also ablated the DPB-induced potentiation of β-adrenoceptor responsiveness. Collectively, these data demonstrate that: 1) PKC activation enhances TSM relaxant responsiveness to β-adrenoceptor stimulation; 2) inhibition of the airway Na+-K+ pump markedly blunts the relaxant response to β-adrenoceptor stimulation; and 3) inhibition of the Na+-K+ pump abolishes the above potentiating effect of DPB on β-adrenoceptor-mediated relaxation of rabbit TSM. Thus, the above findings provide new evidence that PKC activation enhances the airway relaxant response to β-adrenoceptor stimulation, and that the latter effect is dependent on potentiated stimulation of the airway electrogenic Na+-K+ pump.