title: Arecoline inhibits intermediate-conductance calcium-activated potassium channels in human glioblastoma cell lines.
abstract: Arecoline (ARE) is an alkaloid-type natural product from areca nut. This compound has numerous pharmacological and toxicological effects. Whether this agent interacts with ion channels to perturb functional activity of cells remains unknown. The effects of ARE on ionic currents were studied in glioma cell lines (U373 and U87MG) using patch-clamp technique. Like TRAM-34(1-[(2-chlorophenyl)-diphenylmethyl]pyrazole), ARE suppressed the amplitude of whole-cell voltage-gated K(+) currents in U373 cells elicited by a ramp voltage clamp. In cell-attached configuration, ARE did not modify the single-channel conductance of intermediate-conductance Ca(2+)-activated K(+) (IKCa) channels; however, it did reduce channel activity. Its inhibition of IKCa channels was accompanied by a significant lengthening in the slow component of mean closed time of IKCa channels. Based on minimal kinetic scheme, the dissociation constant (KD) required for ARE-mediated prolongation of mean closed time was 11.2µM. ARE-induced inhibition of IKCa channels was voltage-dependent. Inability of ARE to perturb the activity of large-conductance Ca(2+)-activated K(+) (BKCa) channels was seen. Under current-clamp recordings, ARE depolarized the membrane of U373 cells and DCEBIO reversed ARE-induced depolarization. Similarly, ARE suppressed IKCa-channel activities in oral keratinocytes. This study provides the evidence that ARE block IKCa channels in a concentration, voltage and state-dependent manner. ARE-induced block of IKCa channels is unrelated to the binding of muscarinic receptors. The effects of ARE on these channels may partially be responsible for the underlying cellular mechanisms by which it influences the functional activities of glioma cells or oral keratinocytes, if similar findings occur in vivo.
authors.affiliation: Department of Anesthesia & Medical Research, China Medical University - An Nan Hospital, Tainan City, Taiwan; Department of Anesthesia, China Medical University, Taichung City, Taiwan; Department of Anesthesia, Nan Shan branch of Gilu Hospital, Shandong University, Shandong Province, PR China.
authors.forename: Edmund Cheung
authors.initials: EC
authors.lastname: So
authors.affiliation: Department of Physiology, National Cheng Kung University Medical College, No. 1 University Road, Tainan City 70101, Taiwan.
authors.forename: Yan-Ming
authors.initials: YM
authors.lastname: Huang
authors.affiliation: Department of Anesthesia, Chi Mei Medical Center, Tainan City, Taiwan.
authors.forename: Chung-Hsi
authors.initials: CH
authors.lastname: Hsing
authors.affiliation: Department of Physiology, National Cheng Kung University Medical College, No. 1 University Road, Tainan City 70101, Taiwan.
authors.forename: Yu-Kai
authors.initials: YK
authors.lastname: Liao
authors.affiliation: Department of Physiology, National Cheng Kung University Medical College, No. 1 University Road, Tainan City 70101, Taiwan. Electronic address: snwu@mail.ncku.edu.tw.
authors.forename: Sheng-Nan
authors.initials: SN
authors.lastname: Wu
mesh_terms: D001115:Arecoline / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D001562:Benzimidazoles / Q000494:pharmacology; D002460:Cell Line; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors*; D007700:Kinetics; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D061251:Primary Cell Culture; D011720:Pyrazoles / Q000494:pharmacology
chemical_list: C507351:5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one; D001562:Benzimidazoles; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C494841:KCNMA1 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D026902:Potassium Channel Blockers; D011720:Pyrazoles; C411671:TRAM 34; D001115:Arecoline
keywords: Arecoline; Glioma cells; Intermediate-conductance Ca(2+)-activated K(+) channel; K(+) current