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Dihydropyridine‐sensitive and omega‐conotoxin‐sensitive calcium channels in a mammalian neuroblastoma‐glioma cell line.
Author(s) -
Kasai H,
Neher E
Publication year - 1992
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1992.sp019035
Subject(s) - chemistry , nifedipine , dihydropyridine , calcium channel , patch clamp , biophysics , omega , voltage dependent calcium channel , calcium , biochemistry , receptor , biology , physics , organic chemistry , quantum mechanics
1. Pharmacological and kinetic properties of high‐voltage‐activated (HVA) Ca2+ channel currents were studied using the whole‐cell and perforated patch‐clamp methods in a mouse neuroblastoma and rat glioma hybrid cell line, NG108‐15, differentiated by dibutyryl cyclic AMP or by prostaglandin E1 and theophylline. 2. The HVA currents were separated into two components by use of two organic Ca2+ channel antagonists, omega‐conotoxin GVIA (omega CgTX) and a dihydropyridine (DHP) compound, nifedipine. One current component, IDHP, was blocked by nifedipine (Kd = 8.2 nM) and was resistant to omega CgTX. Conversely, the other component, I omega CgTX, was irreversibly blocked by omega CgTX and was resistant to DHPs. Thus, IDHP could be studied in isolation by a short application of omega CgTX, while I omega CgTX could be studied in the presence of nifedipine. 3. The voltage for half‐activation of IDHP was smaller than that of I omega CgTX by 13 mV. IDHP was activated at potentials that were subthreshold for voltage‐dependent K+ currents of the cell, whereas I omega CgTX was not. 4. Time courses of activation and deactivation of IDHP were faster than those of I omega CgTX. 5. Voltage‐dependent inactivation was small for both IDHP and I omega CgTX at any potential. 6. Ca(2+)‐dependent inactivation of IDHP was faster and more prominent than that of I omega CgTX. The time course of the Ca(2+)‐dependent inactivation of IDHP, but not I omega CgTX, was slowed as the membrane potential was made more positive between ‐20 and 30 mV, although amplitude of the current was increased. 7. Alkaline earth metal ions carried the two components of IHVA in the same order: Ba2+ greater than Sr2+ greater than Ca2+. 8. Metal ions blocked the two components of IHVA in the same order of potency: Gd3+ greater than La3+ greater than Cd2+ greater than Cu2+ greater than Mn2+ greater than Ni2+. 9. An alkylating agent, N‐ethylmaleimide (NEM, 0.1 mM), selectively augmented IDHP by 30%. 10. During the course of cellular differentiation induced by dibutyryl cyclic AMP, IDHP appeared earlier than I omega CgTX. 11. These results indicate that two classes of Ca2+ channels contribute to the HVA currents of this cell line. The DHP‐sensitive channel is more apt to generate Ca2+ spikes and Ca2+ plateau potentials than the omega CgTX‐sensitive channel.