Biophysical and Pharmacological Properties of Voltage-gated Calcium Channels in Osteoblastic MC3T3-E1 Cells

The electrophysiological and pharmacological properties of the voltage-gated Ca2+ channels in MC3T3-E1 cells were analyzed using the perforated whole-cell patch-clamp technique. When the voltage was depolarized by step pulses from a holding potential of -104mV, the cells displayed transient inward currents (-4.25±0.25pA/pF, n=16) in 10mM Ba2+ solution. The activation threshold for the inward Ba2+current was about -60mV and the peak existed between -40 and -20mV. The steady state activation and inactivation properties of the inward Ba2+ current generated a window current in the range of -70 to -40 mV. Gd2+ (0.1mM) inhibited the inward Ba2+ currents by about 60%. Ni2+ (0.1mM, a blocker for T-type and R-type Ca2+ channels at this concentration), nifedipine (5μM, L-type Ca2+ channel blocker), ω-conotoxin GVIA (3μM, N-type Ca2+ channel blocker) and ω-agatoxin TK (200nM, a P/Q-type Ca2+ channel blocker) did not inhibit the currents. Bay K 8644 (0.5μM, a dihydropyridine agonist for L-type Ca2+ channel) also did not affect the Ba2+ currents. The results suggest that Ca2+ channels with novel properties are expressed in MC3T3-E1 cells.