Calcium influx and release in isolated rat osteoclasts.
Intracellular and extracellular sources of cytosolic [Ca2+] elevation in isolated rat osteoclasts were explored by a comparison of fura-2 signals in response to application of the Ca2+ ionophore, ionomycin, in Ca(2+)-containing and in Ca(2+)-free bathing solutions. Cytosolic [Ca2+] transients persisted in osteoclasts bathed in Ca(2+)-free, EGTA-containing solutions. They consisted of a peak cytosolic [Ca2+bd elevation followed by a full decay to baseline and were refractory to manipulations of surface membrane potential through changes in extracellular [K+]. They disappeared upon intracellular Ca2+ store depletion through repeated ionophore applications. They were therefore attributable solely to intracellularly stored Ca2+. In contrast, the fura-2 peaks in osteoclasts exposed to Ca(2+)-containing solutions decayed to sustained levels. Cytosolic [Ca2+] responses then persisted with repeated ionomycin application. These latter phenomena are accordingly attributable to extracellular Ca2+ entry. Finally, restoration of extracellular [Ca2+] to 1.25 mM following the depletion of intracellular Ca2+ stores by treatment with ionomycin elicited a cytosolic [Ca2+] 'overshoot' consistent with capacitative Ca2+ entry via a cytosolic route. These results demonstrate a refillable intracellular source of cytosolic Ca2+ that could function in osteoclastic regulation.
Shankar
V S
VS
Bone Research Unit, St George's Hospital Medical School, London.
Huang
C L
CL
Adebanjo
O A
OA
Pazianas
M
M
Zaidi
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D017136:Ion Transport; D015759:Ionomycin / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D004533:Egtazic Acid; D015759:Ionomycin; D011188:Potassium; D002118:Calcium