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

• Published in: The Journal of pharmacology and experimental therapeutics 2008-10, Vol.327 (1), p.114-123
• Main Authors: Kajioka, Shunichi, Nakayama, Shinsuke, Asano, Haruhiko, Seki, Narihito, Naito, Seiji, Brading, Alison F
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - pharmacology; Animals; ATP-Binding Cassette Transporters - drug effects; ATP-Binding Cassette Transporters - physiology; Calcitonin Gene-Related Peptide - pharmacology; Cromakalim - pharmacology; Cyclic AMP - pharmacology; Glyburide - pharmacology; Guanosine Diphosphate - pharmacology; KATP Channels - drug effects; KATP Channels - physiology; Potassium Channels, Inwardly Rectifying - drug effects; Potassium Channels, Inwardly Rectifying - physiology; Receptors, Drug - drug effects; Receptors, Drug - physiology; Signal Transduction - physiology; Sulfonylurea Receptors; Swine; Urinary Bladder - drug effects; Urinary Bladder - physiology
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.108.140269

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 ∼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 ∼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.