Article date: January 1984
By: I. Engberg, J.A. Flatman, J.D.C. Lambert in Volume 81, Issue 1, pages 215-224
QX‐222 (the trimethyl analogue of lignocaine), methylxylocholine, lignocaine and pentobarbitone were iontophoresed intracellularly into cat lumbosacral motoneurones. Iontophoresis and recording was either from a triple‐barrelled microelectrode unit or from two separately advanced microelectrodes.
QX‐222 and methylxylocholine caused a very slow reversible block of the current‐evoked and antidromic action potentials (AP) with no significant change of membrane potential (EM). Lignocaine had a minimal blocking effect on the AP.
No change, or only a small decrease, of membrane slope conductance (GM) was seen when the APs had been totally abolished.
QX‐222 and methylxylocholine reduced the massive Gm increase evoked by the passage of large depolarizing currents and converted the post‐current hyperpolarization (time constant 120–150 ms) into a depolarization of similar time course. It is suggested that the quaternary local anaesthetics can reduce the fast and slow voltage‐dependent potassium conductances.
Both agents totally blocked AP generation without decreasing the magnitude of the Ia e.p.s.p.
It is suggested that intracellularly iontophoresed QX‐222 (on account of its low lipid solubility) could be used as a pharmacological tool to block specifically the active Na and K channels in only the cell impaled by the microelectrodes.
QX‐222 (the trimethyl analogue of lignocaine), methylxylocholine, lignocaine and pentobarbitone were iontophoresed intracellularly into cat lumbosacral motoneurones. Iontophoresis and recording was either from a triple‐barrelled microelectrode unit or from two separately advanced microelectrodes.
QX‐222 and methylxylocholine caused a very slow reversible block of the current‐evoked and antidromic action potentials (AP) with no significant change of membrane potential (EM). Lignocaine had a minimal blocking effect on the AP.
No change, or only a small decrease, of membrane slope conductance (GM) was seen when the APs had been totally abolished.
QX‐222 and methylxylocholine reduced the massive Gm increase evoked by the passage of large depolarizing currents and converted the post‐current hyperpolarization (time constant 120–150 ms) into a depolarization of similar time course. It is suggested that the quaternary local anaesthetics can reduce the fast and slow voltage‐dependent potassium conductances.
Both agents totally blocked AP generation without decreasing the magnitude of the Ia e.p.s.p.
It is suggested that intracellularly iontophoresed QX‐222 (on account of its low lipid solubility) could be used as a pharmacological tool to block specifically the active Na and K channels in only the cell impaled by the microelectrodes.
DOI: 10.1111/j.1476-5381.1984.tb10763.x
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