Osteoblastic cells have L-type calcium channels.

Whole cell patch clamp studies on osteoblast-like rat osteosarcoma cells (ROS 17/2.8) show the existence of L-type calcium channels in the cell membrane. Measurements were carried out at both 21 and 37 degrees C. With isotonic CsCl in the pipette and a bathing medium containing either 110 or 10 mM Ba2+, a strong depolarizing pulse was required to activate an inward current. The current-voltage relationship (I-V) of this inward current showed a maximum amplitude near +30 mV at 21 and 37 degrees C, with 110 mM Ba2+ in the bathing medium, and near +10 mV at 37 degrees C with 10 mM Ba2+. At both 21 and 37 degrees C the dihydropyridine, BAY K 8644 (2 microM), increased this current and shifted the I-V maximum to less positive potentials, while nifedipine (5 microM) reduced the current. Cd2+ (50 microM) and Co2+ (100 microM) blocked the current. At 21 degrees C the measured inward current showed a slow inactivation, with a time constant of some hundreds of milliseconds. At 37 degrees C, inactivation was considerably faster. The current was suppressed by holding the membrane potential more positive than -30 mV. These data are strong evidence that ROS 17/2.8 cells have a significant number of 'L-type' calcium channels.