Premium
The asymmetrical effects of some ionized n‐octyl derivatives on the sodium current of the giant axon of Loligo forbesi.
Author(s) -
Elliott J R,
Haydon D A,
Hendry B M
Publication year - 1984
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.1984.sp015210
Subject(s) - depolarization , sodium , chemistry , biophysics , extracellular , axon , intracellular , sodium channel , steady state (chemistry) , analytical chemistry (journal) , chromatography , anatomy , biochemistry , biology , organic chemistry
The effects of octyltrimethylammonium ions (OTMA+), octyl sulphate ions (OS‐) and octanoic acid (OA) on the sodium current of the voltage‐clamped squid giant axon have been investigated using intracellular and extracellular application of the test substances. OTMA+ applied externally at concentrations of 0.8‐5.0 mM produces a small reversible increase in the peak inward sodium current in both intact and CsF‐perfused axons. Intracellular application of OTMA+ at 0.8 mM to CsF‐perfused axons causes a reversible 50% suppression of peak inward sodium current. The inhibition of peak inward current by internal OTMA+ arises largely from a shift of the steady‐state activation parameter (m infinity) in the depolarizing direction along the voltage axis. There is little use dependence of the current suppression by OTMA+ OA applied either internally or externally is more effective at suppressing peak inward sodium current at pH 6.0 than at pH 7.4. At pH 6.0 external application of 5 mM‐OA to perfused axons causes approximately 60% suppression. This is associated with a depolarizing shift of m infinity of about 13 mV and a hyperpolarizing shift of the steady‐state inactivation (h infinity) curve of about 4 mV. The effects of internal and external OA are broadly similar except that the h infinity shift is not seen with internal application. OS‐ at concentrations above 2.0 mM produces complete irreversible loss of sodium current. At 2.0 mM, OS‐ produces 10% current suppression and a small depolarizing shift of the m infinity curve. Internal and external applications of OS‐ differ little except that external OS‐ causes a 25% increase in the time constant of activation (tau m). The possible origins of these effects are discussed. It is proposed that the shift of m infinity caused by internal OTMA+ is due to a diminution of the lipid dipole potential at the internal surface of the membrane caused by OTMA+ adsorption. This effect could also account for the m infinity shift caused by OA. The results showing that OA produces shifts of opposite sign in the voltage dependence of m infinity and h infinity are discussed with respect to their implications for models of sodium channel gating.