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The influence of charge on the effects of n‐octyl derivatives on sodium current inactivation in rat sensory neurones.
Author(s) -
Elliott A A,
Elliott J R
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.sp018694
Subject(s) - depolarization , chemistry , sodium , steady state (chemistry) , molar concentration , current (fluid) , biophysics , analytical chemistry (journal) , physics , thermodynamics , chromatography , biology , organic chemistry
1. The whole‐cell patch‐clamp technique was used to determine the actions of n‐octyl sulphate (OS‐) anions and n‐octyl trimethylammonium (OTMA+) cations on sodium current steady‐state inactivation and peak amplitude in cells isolated from dorsal root ganglia of neonatal rats and maintained in short‐term tissue culture. This paper concentrates on the effects of external addition but the actions of internal OS‐ and OTMA+ are briefly considered. 2. The main action of external OS‐ was to cause a hyperpolarizing shift in the voltage dependence of the steady‐state inactivation parameter, h infinity. At 1‐6 mM OS‐ caused a shift in the mid‐point of the h infinity curve of around ‐30 mV. The shape of the h infinity curve was altered in a concentration‐dependent manner. Internal OS‐ had no discernible effect on the shape or position of the h infinity curve. 3. External OS‐ produced a relatively small (less than 25%) reduction in the maximum current achieved following pre‐pulses sufficiently negative to remove resting steady‐state inactivation. 4. By contrast, external OTMA+ had little effect on the voltage dependence of h infinity and produced a small, but significant, increase in the maximum sodium current. 2 mM‐external OTMA+ moved the mid‐point of the h infinity curve (Vh) 5 mV in the depolarizing direction (relative to the mean of control and reversal curves) and increased the maximum current by 13%. One millimolar internal OTMA+ induced a frequency‐dependent current block. 5. Raising the external calcium concentration from 2 to 20 mM (in the presence of 2 mM‐magnesium and 5 mM‐cobalt) caused an 18 mV depolarizing shift in Vh, consistent with a reduction in the negativity of an external surface charge. The maximum current was reduced by 22%. 6. One millimolar OS‐ reduced the surface potential of egg phosphatidylcholine (EPC) monolayers (at an air‐0.5 M‐NaCl interface) by 35 mV but 1 or 2 mM‐OTMA+ produced only a 2‐3 mV increase. The quantitative agreement between the effects of OS‐, on Vh in the rat and on monolayer surface potential, decreased with increasing concentration.(ABSTRACT TRUNCATED AT 400 WORDS)