Expression of voltage-operated Ca2+ channels in rat bone marrow stromal cells in vitro.

The expression of voltage-operated Ca2+ currents (VOCCs) in bone marrow stromal cells cultured for 3-30 days has been studied by the use of the whole-cell patch-clamp technique. Both low-voltage-activated (LVA) and high-voltage-activated (HVA) VOCCs were recorded. LVA currents were first detectable after 6-7 days in culture and reached a peak of expression at 8 days, after which both the amplitude and frequency of expression of the current fell rapidly. The current was virtually undetectable in cells cultured for more than 15 days. The HVA current was detectable after 3 days in culture and reached a peak of both amplitude and frequency of expression after 1-2 weeks. This current was expressed consistently throughout the remaining culture period. In cultures treated with dexamethasone (10(-8) mol/L) peak expression of LVA currents still occurred at 7-8 days, but currents were enhanced approximately threefold. Expression of LVA currents was maintained to the end of the culture period. Expression of HVA currents was not significantly modified by treatment of cultures with dexamethasone. Examination of the biophysical and pharmacological (blockade by Ni2+ and diphenylhydantoin) properties of the LVA current in these cells suggests that they may have similarities with the LVA T currents of neuronal cells.