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 micromol/L), continuously increased the membrane conductance, and the reversal potential was -12.5+/-5.0 mV (n=5). Extracellularly applied neomycin (100 micromol/L) and Gd3+ (100 micromol/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.
Yoshida
N
N
Department of Orthodontics, Nagasaki University School of Dentistry, Sakamoto, Japan.
Sato
T
T
Kobayashi
K
K
Okada
Y
Y
D000199:Actins / Q000032:analysis; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000819:agonists*; D002712:Chlorides / Q000494:pharmacology; D004553:Electric Conductivity; D007473:Ion Channels / Q000187:drug effects*; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009355:Neomycin / Q000494:pharmacology; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
D000199:Actins; D002135:Calcium-Binding Proteins; D002712:Chlorides; D007473:Ion Channels; D007476:Ionophores; D011500:Protein Synthesis Inhibitors; D002104:Cadmium; D015759:Ionomycin; D003994:Bucladesine; D009355:Neomycin; D002118:Calcium