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On the sodium and potassium currents of a human neuroblastoma cell line.
Author(s) -
Ginsborg B L,
Martin R J,
Patmore L
Publication year - 1991
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.1991.sp018462
Subject(s) - depolarization , chemistry , potassium , repolarization , sodium , patch clamp , voltage clamp , time constant , biophysics , analytical chemistry (journal) , membrane potential , electrophysiology , medicine , chromatography , biochemistry , receptor , organic chemistry , engineering , electrical engineering , biology
1. The patch‐clamp method was applied to the study of ionic currents activated by depolarization of undifferentiated IMR‐32 human neuroblastoma cells. Whole‐cell sodium and potassium currents and single potassium ion channel currents from cell‐attached patches were investigated. 2. Cells had a mean resting potential of ‐38 mV and mean input resistance of 1.6 G omega. Single action potentials were evoked under current clamp during the injection of depolarizing currents. 3. A voltage‐dependent inward sodium current was observed which reversed at +44 mV. A Boltzmann fit to the activation curve gave a half‐maximal activation voltage of ‐41.6 mV and a 'slope' of 3.9 mV. The steady‐state inactivation curve had a half‐maximal inactivation voltage of ‐81 mV and a 'slope' of 9.7 mV. 4. The time‐dependent activation and inactivation of the current displayed classical Hodgkin‐Huxley kinetics. Values for the time constants tau m and tau h of 0.16 and 0.63 ms were calculated for a voltage jump from ‐80 to ‐10 mV; tau m and tau h decreased as the step potential was changed from ‐30 to +20 mV. 5. Outward currents were activated in bathing solutions substantially free of anions and could thus be attributed to potassium ions. The tail current reversed in direction on repolarization to ‐60 mV when the potassium concentration in the bathing solution was increased from 6 to 30 mM. When the bathing solution contained 145 mM‐potassium, and the patch pipette, 95 mM, a depolarization to ‐10 mV from a holding potential of ‐60 mV evoked an inward current. 6. Outward currents were examined by using voltage pulses which depolarized the cell to ‐20 mV, or more positive values, from a holding potential of ‐80 mV and by pulses which depolarized the cell to 0 mV, or to positive values, from a holding potential of ‐30 mV. A Boltzmann fit of typical activation data gave a half‐maximal activation voltage of 17 mV and a 'slope' of 14 mV. 7. The time course of the rising phase of the current was described by a function of the form A(1‐exp[‐(t‐delta t)/tau]), where delta t varied between 1 and 4 ms and tau varied between 4 and 27 ms, decreasing with increasing depolarization. There was no evidence for a fast transient component. 8. The amplitude of outward currents was reduced by extracellular calcium ions, cobalt ions, tetraethylammonium and 4‐aminopyridine.(ABSTRACT TRUNCATED AT 400 WORDS)