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Characterization of two types of calcium channels in mouse neuroblastoma cells
1. Two types of voltage-sensitive calcium channels were identified and studied in the neuroblastoma cell line N1E-115. Calcium channel currents as carried by Ba2+ (50 mM) were recorded using the whole-cell variation of the patch-electrode voltage-clamp technique. 2. A transient (type I) inward Ba2+...
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Published in: | The Journal of physiology 1987-02, Vol.383 (1), p.231-249 |
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Main Authors: | , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that cite this one |
Online Access: | Get full text |
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Summary: | 1. Two types of voltage-sensitive calcium channels were identified and studied in the neuroblastoma cell line N1E-115. Calcium
channel currents as carried by Ba2+ (50 mM) were recorded using the whole-cell variation of the patch-electrode voltage-clamp
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 microM): La3+, 1.5 much greater than Ni2+, 47 greater than Cd2+, 160 = Co2+, 160 for type I channels, and La3+,
0.9 greater than Cd2+, 7.0 much greater than Ni2+, 280 greater than 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 degrees C. The temperature
coefficient (Q10) value was estimated to be 3.0 between 20 and 30 degrees C, and 15.0 below 20 degrees C. Above 30 degrees
C, warming reduced the amplitude slightly. 10. External application of dibutyryl adenosine 3',5'-phosphate (dibutyryl cyclic
AMP) (1 mM) caused an increase in the amplitude of the type II current by 30-50%, while failing to enhance the type I component. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.1987.sp016406 |