title: Levcromakalim and MgGDP activate small conductance ATP-sensitive K+ channels of K+ channel pore 6.1/sulfonylurea receptor 2A in pig detrusor smooth muscle cells: uncoupling of cAMP signal pathways.
abstract: Pharmacological studies have suggested the existence of ATP-sensitive K(+) (K(ATP)) channel as a therapeutic target in urinary bladders; however, electrical properties have not yet been shown. Patch-clamp techniques were applied to investigate the properties of K(ATP) channels in pig detrusor cells. In whole-cell configuration, levcromakalim, a K(ATP) channel opener, induced a long-lasting outward current in a concentration-dependent manner. The current-voltage curve of the levcromakalim-induced membrane current intersected at approximately -80 mV. This current was abolished by glibenclamide. Intracellular application of 0.1 mM GDP significantly enhanced the levcromakalim-induced membrane current, whereas cAMP did not. Furthermore, neurotransmitters related to cAMP signaling, such as calcitonin gene-related peptide, vasointestinal peptide, adenosine, and somatostatin, had little effect on the membrane current. In cell-attached configuration, levcromakalim activated K(+) channels with a unitary conductance of approximately 12 pS. When the patch configuration was changed to inside-out mode, the K(+) channel activity ran down. Subsequent application of 1 mM GDP reactivated the channels. The openings of the approximately 12 pS K(+) channels in the presence of 1 mM GDP was suppressed by ATP and glibenclamide. In reverse transcription-polymerase chain reaction, K(+) channel pore 6.1 and sulfonylurea receptor (SUR)2A were predominant in pig detrusor cells. The 12 pS K(+) channel activated by levcromakalim in pig detrusor smooth muscle cells is a K(ATP) channel. The predominant expression of SUR2A can account for the lack of effect of neurotransmitters related to cAMP.
authors.affiliation: University Department of Pharmacology, Oxford, United Kingdom.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Kajioka
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Nakayama
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Asano
authors.forename: Narihito
authors.initials: N
authors.lastname: Seki
authors.forename: Seiji
authors.initials: S
authors.lastname: Naito
authors.forename: Alison F
authors.initials: AF
authors.lastname: Brading
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000187:drug effects* / Q000502:physiology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D019806:Cromakalim / Q000494:pharmacology*; D000242:Cyclic AMP / Q000494:pharmacology*; D005905:Glyburide / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000494:pharmacology*; D054086:KATP Channels / Q000187:drug effects* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects* / Q000502:physiology; D011955:Receptors, Drug / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D064233:Sulfonylurea Receptors; D013552:Swine; D001743:Urinary Bladder / Q000187:drug effects* / Q000502:physiology
chemical_list: D018528:ATP-Binding Cassette Transporters; D054086:KATP Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; C092520:uK-ATP-1 potassium channel; D019806:Cromakalim; D006153:Guanosine Diphosphate; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D015740:Calcitonin Gene-Related Peptide; D005905:Glyburide