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Ionic currents in cultured mouse neuroblastoma cells under voltage‐clamp conditions.
Author(s) -
Moolenaar W H,
Spector I
Publication year - 1978
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.1978.sp012303
Subject(s) - tetrodotoxin , reversal potential , depolarization , tetraethylammonium , chemistry , biophysics , conductance , membrane potential , voltage clamp , cardiac transient outward potassium current , resting potential , patch clamp , potassium , biochemistry , physics , biology , receptor , organic chemistry , condensed matter physics
1. Ionic currents in differentiated cells of mouse neuroblastoma clone N1E‐115 have been studied under voltage‐clamp conditions. 2. Depolarizing voltage steps from a holding potential of ‐85 mV to levels more positive than ‐40 mV produced fast transient inward currents followed by delayed outward currents. 3. The fast inward current is carried by Na+: it is blocked by tetrodotoxin and is absent in Na+‐free solutions. Its kinetic behaviour resembles that of the Na+ current in squid giant axon. A mean value of 85 mmho/cm2 was found for the maximum Na+ conductance (GNa).4. The delayed outward current is carried primarily by K+: it is blocked by externally applied tetraethylammonium (TEA, 15 mM) and has a reversal potential (mean ‐71 mV) close to the theoretical K+ equilibrium potential. Its instantaneous I‐‐V curve is linear. By analogy with the formulation of Hodgkin & Huxley (1952c), the outward current can be described by IK = ‐GKn2(V‐‐EK) where GK = 12 mmho/mc2. 5. During prolonged depolarizations the delayed outward current declines. This decline, which occurs in two phases, represents a partial inactivation of the K+ conductance. 6. A weak inward current with slow activation and inactivation kinetics appears in Na+‐free solution containing 10 mM‐Ca2+. It is activated at a membrane potential of ‐55 mV and reaches its maximum at ‐20 mV with a time to peak of about 10 msec. This current is tetrodotoxin‐resistant, reversibly blocked by Co2+ (5mM) and is suggested to be carried by Ca2+. 7. An increase in the external divalent cation concentration results in a parallel shift of the steady‐state I‐‐V curve along the voltage axis in positive direction. The activation of delayed outward currents is suggested not to depend on Ca2+ influx. 8. It is concluded that separate voltage‐dependent Na+, K+ and Ca2+ channels exist in the differentiated neuroblastoma membrane with kinetic and pharmacological properties similar to those observed in non‐mammalian preparations.