Low-voltage-activated calcium channels in human retinoblastoma cells

Retinoblastoma cells represent pluripotent neural-progenitor cells which, if induced to differentiate, express many features of mature human retinal neurons. Ca channel currents were recorded from isolated, undifferentiated human retinoblastoma Y79 cells in a bath solution containing 20 mM BaCl2 using whole-cell patch-clamp pipettes containing CsCl. The transient, macroscopic currents inactivated with a time constant of about 20 ms at -20 mV and had other properties similar to low-voltage-activated calcium channels described in other cell types: Activation curves fit by the Boltzmann relation had a midpoint of -32 mV and a slope factor of 6.8 mV (-80 mV holding potential) and inactivation curves had a midpoint of -40 mV and a slope factor of 3.7 mV. Non-stationary fluctuation analysis of the currents performed over a 2 kHz bandwidth indicated that each channel contributed 0.44 pA to the macroscopic transient current at -20 mV, suggesting a unitary conductance of about 7 pS.