High Extracellular Ca2 Stimulates Ca2 -Activated Cl− Currents in Frog Parathyroid Cells through the Mediation of Arachidonic Acid CascadeReport as inadecuate




High Extracellular Ca2 Stimulates Ca2 -Activated Cl− Currents in Frog Parathyroid Cells through the Mediation of Arachidonic Acid Cascade - Download this document for free, or read online. Document in PDF available to download.

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 12S-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.



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

Source: http://plos.srce.hr/



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