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Fast inward‐rectifying current accounts for anomalous rectification in olfactory cortex neurones.
Author(s) -
Constanti A,
Galvan M
Publication year - 1983
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.1983.sp014526
Subject(s) - rectification , neuroscience , olfactory system , current (fluid) , biophysics , chemistry , biology , physics , voltage , quantum mechanics , thermodynamics
The somatic membrane of guinea‐pig olfactory cortex neurones in vitro (23 degrees C) was voltage clamped by means of a single‐micro‐electrode sample‐and‐hold technique. In most cells the current‐voltage (I‐V) relationship showed inward (anomalous) rectification with increasing hyperpolarization beyond the resting potential (ca. ‐80 mV). Under current‐clamp conditions a time‐dependent ‘sag’ of the hyperpolarizing electrotonic potentials was observed following an initial overshoot. No depolarizing after‐potential was seen on return to the resting potential. Inward rectification was activated between ‐100 and ‐110 mV (irrespective of pre‐set resting potential) and increased the membrane input conductance by up to three‐fold. The rectification was unaffected by tetrodotoxin or Cd2+. Under somatic voltage clamp, hyperpolarization beyond ‐110 mV activated a rapid inward relaxation fitted by a single exponential. The relaxation time constant (tau on) decreased e‐fold for a 40 mV hyperpolarization. (Typical values: 28 ms at ‐110 mV declining to 13 ms at ‐140 mV; external K+ concentration 3 mM, 23 degrees C). More extreme hyperpolarizations evoked a slower ‘inactivation’ phase (tau = 40‐60 ms). A transient outward‐decaying ‘tail’ current reflecting deactivation of inward rectification was seen on stepping from ‐140 mV to more positive potentials. tau off became slower with hyperpolarization. The tail current disappeared at a potential close to the expected VK but was rarely inverted to an inward‐decaying tail. It is proposed that the fast inward‐rectifying current of olfactory neurones (If.i.r.) is a K+ current analogous to the anomalous K+ rectifier of marine egg and frog muscle membranes. The behaviour of the inward rectifier was dependent on external K+ concentration in accordance with the unique ‘V‐‐VK’ dependence of classical anomalous rectification; however, of several agents tested (external Cs+, Ba2+, Rb+, Tl+ or tetraethylammonium), only Cs+ and Ba2+ blocked If.i.r. in a time‐ and voltage‐dependent manner. The effect of tetraethylammonium resembled that of an increase in external K+. The possible contribution of the inward rectifier to the passive cell membrane properties is discussed.