High Extracellular Ca2+ Stimulates Ca2+-Activated Cl− Currents in Frog Parathyroid Cells through the Mediation of Arachidonic Acid Cascade

by Yukio Okada, Kotapola G. Imendra, Toshihiro Miyazaki, Hitoshi Hotokezaka, Rie Fujiyama, Kazuo Toda

Elevation of extracellular Ca²⁺ concentration induces intracellular Ca²⁺ signaling in parathyroid cells. The response is due to stimulation of the phospholipase C/Ca²⁺ pathways, but the direct mechanism responsible for the rise of intracellular Ca²⁺ concentration has remained elusive. Here, we describe the electrophysiological property associated with intracellular Ca²⁺ signaling in frog parathyroid cells and show that Ca²⁺-activated Cl⁻ channels are activated by intracellular Ca²⁺ increase through an inositol 1,4,5-trisphophate (IP₃)-independent pathway. High extracellular Ca²⁺ induced an outwardly-rectifying conductance in a dose-dependent manner (EC₅₀∼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 Ca²⁺-induced and Ca²⁺ dialysis-induced currents reversed at the equilibrium potential of Cl⁻ and were inhibited by niflumic acid (a specific blocker of Ca²⁺-activated Cl⁻ channel). Gramicidin-perforated whole-cell recording displayed the shift of the reversal potential in extracellular Ca²⁺-induced current, suggesting the change of intracellular Cl⁻ concentration in a few minutes. Extracellular Ca²⁺-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 Ca²⁺-induced current. IP₃ 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 Ca²⁺-induced conductance. These results indicate that high extracellular Ca²⁺ raises intracellular Ca²⁺ concentration through the DAG lipase/lipoxygenase pathway, resulting in the activation of Cl⁻ conductance.

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High Extracellular Ca2+ Stimulates Ca2+-Activated Cl− Currents in Frog Parathyroid Cells through the Mediation of Arachidonic Acid Cascade
Syndicated from:PLoS ONE

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