The response of cat spinal motoneurones to the intracellular application of agents with local anaesthetic action.
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 channels in only the cell impaled by the microelectrodes.
D000200:Action Potentials / Q000187:drug effects; D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D002415:Cats; D002794:Choline / Q000494:pharmacology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D008012:Lidocaine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D008839:Microelectrodes; D009046:Motor Neurons / Q000187:drug effects*; D009431:Neural Conduction / Q000187:drug effects
D000779:Anesthetics, Local; C006072:QX-222; C008515:methylxylocholine; D008012:Lidocaine; D002794:Choline