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.
Leucine-enkephalin, methionine-enkephalin, and morphine caused a reversible block of Ca21 channel currents in neuroblastoma-glioma hybrid cells (NG108-15
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