| Abstract: | Dorsal root ganglion cells (DRGs) exhibit 3 types of voltage-dependent calcium channels. We have cultured DRGs from 2- to 4-day-old rat pups and obtained whole-cell patch-clamp recordings of calcium-channel currents after 1–5 days in culture. The calcium-channel currents (carried by barium) were recorded with tetrodotoxin (TTX) in the external solution. A cesium-based solution containing Na-ATP, HEPES and EGTA was used in the recording pipette. Cells were held at −80 mV and calcium channel currents were evoked by stepping to depolarized voltages. The divalent cation zinc (Zn2+) blocked sustained and transient voltage sensitive calcium channel currents. Onset of the blockade was fast and a steady-state was reached within 5–15 min, depending upin the concentration used. The IC50 for inhibition of the peak current evoked by a step depolarization from −80 mV to 0 mV (N plus L channels) for 80 ms was 69 μM Zn2+ and the Hill slope about 1. The calcium current evoked by a voltage step from −80 mV to voltages between −40 mV and −15 mV (T-type current) was more sensitive (> 80% block with 20 μM Zn2+). During wash the effect was only partly reversible in 50% of the neurons. Thus, Zn2+ is a potent blocker of voltage dependent calcium currents in mammalian neurons, especially of T-type currents. |
