title: The effect of sodium transport and calcium channel inhibitors on phorbol ester-induced contraction of bovine airway smooth muscle.
abstract: We studied the role of sodium transport and calcium channels in protein kinase C mediated signal-transduction pathways in bovine airway smooth muscle. 4-beta phorbol 12,13 dibutyrate (PDB), an activator of protein kinase C, caused dose-related slowly developing contraction in bovine bronchial rings with a peak effect at 60-90 min. 4-alpha PDB, an inactive analogue, was without effect. Mean peak PDB-induced contraction (measured as a percentage of the maximum response to methacholine) was reduced from 122% to 20% when experiments were carried out in calcium-free fluids +EDTA (10(-3) M). Similar reductions were seen in the presence of nifedipine and verapamil, inhibitors of voltage-dependent calcium channels. Amiloride at high concentrations (10(-3) M) reduced the contractile response to PDB from 87% to 20%, but at a concentration which inhibits the sodium entry channel (10(-6) M), amiloride was without effect. 5-N,N-hexamethylene amiloride (10(-5) M), a specific inhibitor of Na+/H+ exchange, did not alter the contraction produced by PDB. Frusemide (10(-5) M), an inhibitor of Na(+)-K(+)-Cl- cotransport, was without effect on PDB contractions. We conclude that phorbol ester-induced contraction of bovine airway smooth muscle is dependent on calcium entry via voltage-dependent calcium channels but is independent of Na+ entry, Na+/H+ exchange or Na(+)-K(+)-Cl- cotransport.
authors.affiliation: Respiratory Medicine Unit, City Hospital, Nottingham, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Knox
authors.forename: D R
authors.initials: DR
authors.lastname: Baldwin
authors.forename: E J
authors.initials: EJ
authors.lastname: Cragoe
authors.forename: P
authors.initials: P
authors.lastname: Ajao
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001980:Bronchi / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002417:Cattle; D004347:Drug Interactions; D004492:Edetic Acid / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D010455:Peptides / Q000494:pharmacology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000502:physiology; D014325:Tromethamine / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; C074097:Krebs-Henseleit solution; D010455:Peptides; D015222:Sodium Channels; C029311:serum sodium transport inhibitor; D014325:Tromethamine; C057360:5-(N,N-hexamethylene)amiloride; D015240:Phorbol 12,13-Dibutyrate; D000584:Amiloride; D005665:Furosemide; D004492:Edetic Acid; D012964:Sodium; D005947:Glucose; D002118:Calcium