High extracellular Ca2+ and Ca2+-sensing receptor agonists activate nonselective cation conductance in freshly isolated rat osteoclasts

The effects of an increase of extracellular and intracellular Ca2+ on the membrane properties were examined in freshly isolated rat osteoclasts using the perforated patch-clamp method. Spread-type osteoclasts plated on a cover glass predominantly displayed an inwardly rectifying K+ current in a normal saline solution. Application of an extracellular high-Ca2+ solution transiently increased the membrane conductance in 15 (71%) of 21 osteoclasts. The external high Ca2+- induced current reversed at the membrane potential of -4.8 +/- 2.4 mV (n = 8), The change of intracellular Cl- concentration did not affect the reversal potential, suggesting that the response was due to a nonselective cation conductance, Application of a calcium ionophore, ionomycin (3 mu mol/L), continuously increased the membrane conductance, and the reversal potential was -12.5 +/- 5.0 mV (n = 5), Extracellularly applied neomycin (100 mu mol/L) and Gd3+ (100 mu mol/L), which are agonists of Ca2+-sensing receptor (CaR), also increased the membrane conductance, These results suggest that rat osteoclasts detect high extracellular Ca2+ by an extracellular Ca2+-sensing mechanism functionally similar to the CaR in the cell surface, release Ca2+ from the internal stores, and display the activation of Ca2+-dependent cation channels in the cell membrane. (C) 1998 by Elsevier Science Inc. All rights reserved.