A dihydropyridine-sensitive calcium channel in rodent osteoblastic cells

Rat osteogenic sarcoma cells (UMR 106-01) and normal rat trabecular bone osteoblasts (ROB) were studied using the whole cell version of the patch clamp technique to determine the existence of calcium (Ca²⁺) channels. Pipette and bath solutions were designed to separate Ca²⁺ channel currents from other voltage-dependent currents, and Ba²⁺ was used as the charge carrier. In both UMR 106-01 and ROB cells, a Ba²⁺ current was measured, which expressed the characteristics of an L-channel, such as activation range, dihydropyridine sensitivity, and little or no inactivation. In some cases, this channel was detectable only with BAY-K-8644 in the bath solution. The dihydropyridine agonist increased the current intensity and shifted the peak inward current to more negative potentials. This study, confirming previous observations, demonstrates the existence of a Ca²⁺ channel in both transformed and normal osteoblastic cells.