AJP - Cell Physiology, Vol 267, Issue 4 C1103-C1111, Copyright © 1994 by American Physiological Society
Voltage-activated potassium currents of rabbit osteoclasts: effects of extracellular calcium
L. G. Hammerland, A. S. Parihar, E. F. Nemeth and M. C. Sanguinetti
NPS Pharmaceuticals, Salt Lake City, Utah 84108.
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.
