Characterization of two types of calcium channels in mouse neuroblastoma cells.

Abstract

SUMMARY1. Two types of voltage-sensitive calcium channels were identified and studied in the neuroblastoma cell line NIE-115. Calcium channel currents as carried by Ba2+ (50 mM) were recorded using the whole-cell variation of the patch-electrode voltageclamp technique.2. A transient (type I) inward Ba2+ current was evoked by a step depolarization from a holding potential of -80 mV to potentials more positive than -50 mV. The current amplitude became maximum around -20 mV.3. A depolarization to potentials more positive than -20 mV evoked a long-lasting (type II) component of the inward Ba2+ current. This component reached its maximum around + 10 mV and did not inactivate during a prolonged depolarizing pulse lasting 400 ms.4. When preceded by a 5 s conditioning pulse to -30 mV, step depolarization failed to evoke a transient current due to inactivation. However, it induced a long-lasting current.5. A transient current isolated as the component sensitive to conditioning depolarization became faster in its time course and smaller in its amplitude with membrane depolarization. The current direction was still inward at + 60 mV.6. From the differential voltage sensitivity and the independent channel activity described above, calcium channels responsible for the transient current (type I channel) and those responsible for the long-lasting current (type II channel) were considered to be two different entities.7. Cd2+ preferentially blocked type II channels, whereas La3+ was a highly potent blocker for both types of calcium channels.8. The relative potency for block by polyvalent cations was as follows (apparent dissociation constant in /LM): La3+, 15 > Ni2+, 47 > Cd2+, 160 = Co2+, 160 for type I channels, and La3+, 0 9 > Cd2+, 7 0 > Ni2+, 280 > Co2+, 560 for type II channels.9. The two types of calcium channels were equally sensitive to the temperature. The current amplitude was reduced by cooling below 30 'C. The temperature coefficient (Q10) value was estimated to be 3-0 between 20 and 30 0C, and 15-0 below 20 'C. Above 30 'C, warming reduced the amplitude slightly.

Calcium currents in pyramidal CA1 neurons in vitro after kindling epileptogenesis in the hippocampus of the rat

“…Firstly, it is harder to separate, in the slice, the sustained calcium current from the leak or residual outward current. Secondly, differences in temperature, 33 calcium concentration 41 and cell size predict the calcium current in the slice to be 10 times larger than in dissociated neurons, which is not the case. This discrepancy can be explained if we assume that current amplitude in the dissociated cells gives an indication of the maximum level of recruitment.…”

Molecular Physiology of Low-Voltage-Activated T-type Calcium Channels

“…Early studies found that LVA channels were more sensitive to block by 50 -100 M nickel than HVA channels (124,152,298). Subsequent studies found that many neuronal T-type channels required Ͼ10-fold higher concentrations for block, with many studies reporting IC 50 values of ϳ300 M ( Table 2).…”

“…The temperature sensitivity of T-type currents has been measured in thalamic neurons (85), DRG neurons (305), N1E-115 neuroblastoma cells (298), and GH 3 cells (343). Heating from 22 to 37°C caused over twofold increases in current amplitudes and accelerated channel activation and inactivation.…”

Impairment of the Ca2+‐Permeable AMPA/Kainate Receptors by Lead Exposure in Organotypic Rat Hippocampal Slice Cultures

“…The cobalt-permeable channels are probably not voltage-dependent Ca 2π channels, as several known voltage-dependent Ca 2π channel blockers had no effects on the accumulation of cobalt. In fact, cobalt itself is known to block voltage-dependent Ca 2π channels (Nachshen 1984;Narahashi et al 1987). The cobalt uptake procedure is largely used to detect the Ca 2π -permeable AMPA/ kainate receptors and reflects the Ca 2π entry through these receptors (Pruss et al 1991;Lu et al 1996).…”