Abstract
Parathyroid cells directly monitor extracellular Ca2+ concentration using Ca receptors (CaR). In isolated frog parathyroid cells, high extracellular Ca2+ concentration induces a large increase in chloride conductance. In the present study, we investigated how extracellular Ca2+ increases parathyroid chloride conductance while recording the whole cell current. High extracellular Ca2+ induced an increase of the inward current at -50 mV in a dose-dependent manner. The apparent EC50 for Ca2+ was about 6 mM. When either U73122 (an inhibitor of PLC), tetrahydrolipstatin (an inhibitor of DAG lipase), methyl arachidonyl fluorophosphonate (MAFP, an inhibitor of MAG lipase) or eicosateraynoic acid (ETYA, an inhibitor of lipoxygenase) was applied extracellularly, the magnitude of extracellular Ca2+-induced current decreased significantly. External MS-PPOH (an inhibitor of epoxygenase) did not affect the current response. Internal dialysis of 2-arachidonyl glycerol (2-AG) induced a Gd3+-sensitive inward current, but internal 2-AG ether did not elicit any response. Internal dialysis of arachidonic acid also induced ETYA-sensitive inward current. The results suggest that the arachidonic acid metabolite is involved in the extracellular Ca2+-sensing of frog parathyroid cells. [J Physiol Sci. 2008;58 Suppl:S199]
