Voltage-activated potassium currents of rabbit osteoclasts: effects of extracellular calcium.
The effects of increased extracellular Ca2+ concentration ([Ca2+]e) were examined on a delayed-rectifier K+ current (IK) and an inward-rectifier K+ current (IK1) in rabbit osteoclasts. Elevation of [Ca2+]e from 1.8 to 18 mM shifted the half point for IK activation by +11.5 mV and the voltage dependence of inactivation by +9.7 mV and slowed the rate of IK activation and deactivation. These effects of elevated [Ca2+]e on IK are consistent with screening of cell surface negative charge. However, elevation of [Ca2+]e increased the voltage-dependent kinetics of IK inactivation at all potentials tested, inconsistent with that predicted by simple surface charge theory. This finding suggests an additional, regulatory role for [Ca2+]e in the gating of IK channels. Some osteoclasts had an IK1, which was decreased when [Ca2+]e was raised from 1.8 to 18 mM. The physiological function of both types of K+ currents remains to be determined, and it is not clear whether these currents are involved with the coupling of cytosolic [Ca2+] to [Ca2+]e.
Hammerland
L G
LG
NPS Pharmaceuticals, Salt Lake City, Utah 84108.
Parihar
A S
AS
Nemeth
E F
EF
Sanguinetti
M C
MC
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D018999:Charybdotoxin; D004553:Electric Conductivity; D005110:Extracellular Space / Q000378:metabolism*; D006859:Hydrogen / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D009994:Osmolar Concentration; D010010:Osteoclasts / Q000502:physiology*; D011188:Potassium / Q000037:antagonists & inhibitors / Q000502:physiology*; D011817:Rabbits; D012604:Scorpion Venoms / Q000494:pharmacology
D012604:Scorpion Venoms; D018999:Charybdotoxin; D006859:Hydrogen; D008274:Magnesium; D011188:Potassium; D002118:Calcium