title: Activation by levcromakalim and metabolic inhibition of glibenclamide-sensitive K channels in smooth muscle cells of pig proximal urethra.
abstract: 1. The effects of levcromakalim (BRL 38227) on ionic currents recorded from pig proximal urethra were investigated by use of tension measurement and patch clamp techniques (conventional whole-cell configuration, nystatin perforated patch, and cell-attached configuration). 2. Levcromakalim (1 microM) caused a relaxation in the resting tone. This levcromakalim-induced relaxation was inhibited by the pretreatment with 1 microM glibenclamide. 3. The resting membrane potential recorded from single cells in current-clamp mode was-36.1 +/- 4.4 mV (n = 5). 4. Levcromakalim induced a concentration-dependent hyperpolarization with a maximum (at > or = 10 microM) close to the theoretical equilibrium potential of potassium (EK). The membrane hyperpolarization caused by 1 microM levcromakalim (24.7 +/- 5.8 mV, n = 4) was abolished by 1 microM glibenclamide. 5. Levcromakalim (100 microM) caused an outward K current in whole-cell recordings which was unaffected by iberiotoxin (300 nM) but abolished by glibenclamide (10 microM). 6. In cell-attached patches, levcromakalim activated a 43 pS K channel which was inhibited by the application of glibenclamide. 7. The metabolic poison, cyanide (CN), also activated a 43 pS K channel which was suppressed by the application of 10 microM glibenclamide. 8. These results indicate that levcromakalim and metabolic inhibition activate the same 43 pS K channel in pig proximal urethra. The resultant urethral hyperpolarization might reduce the usefulness of K channel openers in the treatment of detrusor instability, but be of value in treating outflow obstruction.
authors: University Department of Pharmacology, Oxford.
authors: N
authors: N
authors: Teramoto
authors: A F
authors: AF
authors: Brading
mesh_terms: D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology*; D019806:Cromakalim; D004305:Dose-Response Relationship, Drug; D005260:Female; D005905:Glyburide / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology*; D013552:Swine; D014521:Urethra / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D001578:Benzopyrans; D015221:Potassium Channels; D011758:Pyrroles; D014665:Vasodilator Agents; D019806:Cromakalim; D005905:Glyburide