title: High extracellular Ca2+ stimulates Ca2+-activated Cl- currents in frog parathyroid cells through the mediation of arachidonic acid cascade.
abstract: Elevation of extracellular Ca(2+) concentration induces intracellular Ca(2+) signaling in parathyroid cells. The response is due to stimulation of the phospholipase C/Ca(2+) pathways, but the direct mechanism responsible for the rise of intracellular Ca(2+) concentration has remained elusive. Here, we describe the electrophysiological property associated with intracellular Ca(2+) signaling in frog parathyroid cells and show that Ca(2+)-activated Cl(-) channels are activated by intracellular Ca(2+) increase through an inositol 1,4,5-trisphophate (IP(3))-independent pathway. High extracellular Ca(2+) induced an outwardly-rectifying conductance in a dose-dependent manner (EC(50) ∼6 mM). The conductance was composed of an instantaneous time-independent component and a slowly activating time-dependent component and displayed a deactivating inward tail current. Extracellular Ca(2+)-induced and Ca(2+) dialysis-induced currents reversed at the equilibrium potential of Cl(-) and were inhibited by niflumic acid (a specific blocker of Ca(2+)-activated Cl(-) channel). Gramicidin-perforated whole-cell recording displayed the shift of the reversal potential in extracellular Ca(2+)-induced current, suggesting the change of intracellular Cl(-) concentration in a few minutes. Extracellular Ca(2+)-induced currents displayed a moderate dependency on guanosine triphosphate (GTP). All blockers for phospholipase C, diacylglycerol (DAG) lipase, monoacylglycerol (MAG) lipase and lipoxygenase inhibited extracellular Ca(2+)-induced current. IP(3) dialysis failed to induce conductance increase, but 2-arachidonoylglycerol (2-AG), arachidonic acid and 12S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12(S)-HPETE) dialysis increased the conductance identical to extracellular Ca(2+)-induced conductance. These results indicate that high extracellular Ca(2+) raises intracellular Ca(2+) concentration through the DAG lipase/lipoxygenase pathway, resulting in the activation of Cl(-) conductance.
authors.affiliation: Integrative Sensory Physiology, Graduate School of Biomedical Science, Nagasaki University, Nagasaki, Nagasaki, Japan. okada@nagasaki-u.ac.jp
authors.forename: Yukio
authors.initials: Y
authors.lastname: Okada
authors.forename: Kotapola G
authors.initials: KG
authors.lastname: Imendra
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Miyazaki
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Hotokezaka
authors.forename: Rie
authors.initials: R
authors.lastname: Fujiyama
authors.forename: Kazuo
authors.initials: K
authors.lastname: Toda
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides / Q000737:chemistry*; D004594:Electrophysiology / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015289:Leukotrienes / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D008954:Models, Biological; D009865:Oocytes / Q000378:metabolism; D010280:Parathyroid Glands / Q000378:metabolism*; D011898:Ranidae / Q000502:physiology*; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D002712:Chlorides; D004791:Enzyme Inhibitors; D015289:Leukotrienes; D016718:Arachidonic Acid; C021201:12-HPETE; D010738:Type C Phospholipases; D002118:Calcium