Action potentials in primary osteoblasts and in the MG-63 osteoblast-like cell line

Abstract

Whole-cell patch-clamp analysis revealed a resting membrane potential of -60mV in primary osteoblasts and in the MG-63 osteoblast-like cells. Depolarization-induced action potentials were characterized by duration of 60ms, a minimal peak-to-peak distance of 180ms, a threshold value of -20mV and a repolarization between the spikes to -45mV. Expressed channels were characterized by application of voltage pulses between -150mV and 90mV in 10mV steps, from a holding potential of -40mV. Voltages below -60mV induced an inward current. Depolarizing voltages above -30mV evoked two currents: (a) a fast activated and inactivated inward current at voltages between -30 and 30mV, and (b) a delayed-activated outward current that was induced by voltages above -30mV. Electrophysiological and pharmacological parameters indicated that hyperpolarization activated strongly rectifying K(+) (K(ir)) channels, whereas depolarization activated tetrodotoxin sensitive voltage gated Na(+) (Na(v)) channels as well as delayed, slowly activated, non-inactivating, and tetraethylammonium sensitive voltage gated K(+) (K(v)) channels. In addition, RT-PCR showed expression of Na(v)1.3, Na(v)1.4, Na(v)1.5, Na(v)1.6, Na(v)1.7, and K(ir)2.1, K(ir)2.3, and K(ir)2.4 as well as K(v)2.1. We conclude that osteoblasts express channels that allow firing of action potentials.