Effects of ouabain on human bronchial muscle in vitro.
The effects of ouabain, an inhibitor of the plasmalemmal Na(+)/K(+)-ATPase activity, were examined in human isolated bronchus. Ouabain produced concentration-dependent contraction with -logEC(50)=7.16+/-0.11 and maximal effect of 67+/-4% of the response to acetylcholine (1 mM). Ouabain (10 microM)-induced contraction was epithelium-independent and was not depressed by inhibitors of cyclooxygenase and lipoxygenase, antagonists of muscarinic, histamine H(1)-receptors and alpha-adrenoceptors, or neuronal Na(+) channel blockade. The inhibition of ouabain contraction in tissues bathed in K(+)-free medium, and the inhibition by ouabain of the K(+)-induced relaxation confirm that the contractile action of ouabain is mediated by inhibition of Na(+)/K(+)-ATPase. Furthermore, depolarization (16.4+/-0.9 mV) was observed in human isolated bronchus by intracellular microelectrode recording. Ouabain (10 microM)-induced contractions were abolished by a Ca(2+)-free solution but not by blockers of L-type Ca(2+) channels. In human cultured bronchial smooth muscle cells, ouabain (10 microM) produced a sustained increase in [Ca(2+)](i) (116+/-26 nM) abolished in Ca(2+)-free medium. Incubation with a Na(+)-free medium or amiloride (0.1 mM) markedly inhibited the spasmogenic effect of ouabain thus suggesting the role of Na(+)/Ca(2+) exchange in ouabain contraction while selective inhibitors of Na(+)/H(+)-antiport, Na(+)/K(+)/Cl(-)-antiport, or protein kinase C had no effect. Ouabain (10 microM) failed to increase inositol phosphate accumulation in human bronchus. Ouabain (10 microM) did not alter bronchial responsiveness to acetylcholine or histamine but inhibited the relaxant effects of isoprenaline, forskolin, levcromakalim, or sodium nitroprusside. These results indicate that ouabain acts directly to produce contraction of human airway smooth muscle that depends on extracellular Ca(2+) entry unrelated to L-type channels and involving the Na(+)/Ca(2+)-antiporter.
Cortijo
Julio
J
Departament de Farmacologia, Facultat de Medicina i Odontologia, Universitat de València, Avda. Blasco Ibáñez 17, 46010, Valencia, Spain.
Sarria
Benjamín
B
Mata
Manuel
M
Naline
Emmanuel
E
Advenier
Charles
C
Morcillo
Esteban J
EJ
D000109:Acetylcholine / Q000494:pharmacology; D001980:Bronchi / Q000187:drug effects* / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D019806:Cromakalim / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000096:biosynthesis; D007545:Isoproterenol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D009599:Nitroprusside / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D049994:Sodium Potassium Chloride Symporter Inhibitors; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors; D000254:Sodium-Potassium-Exchanging ATPase / Q000009:adverse effects*; D013997:Time Factors; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D002121:Calcium Channel Blockers; D007295:Inositol Phosphates; D049994:Sodium Potassium Chloride Symporter Inhibitors; D017923:Sodium-Hydrogen Exchangers; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D019806:Cromakalim; D009599:Nitroprusside; D005576:Colforsin; D010042:Ouabain; D006632:Histamine; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol; D000109:Acetylcholine; D002118:Calcium