Steroid anaesthetics: inhibition of depolarization-secretion coupling at the mouse motor nerve terminal

The coupling between nerve terminal depolarization and quantal secretion of acetylcholine at the mouse neuromuscular junction was estimated by measuring the multiplication of the frequency of miniature end-plate potentials (m.e.p.p.s) produced by increasing the concentration of calcium in the medium from 0.1 to 1.0 mM in the presence of 15 mM potassium. Depolarization-secretion coupling was inhibited by the anaesthetic steroids progesterone, pregnanedione, and alphaxalone. The nonanaesthetic steroid delta 16-alphaxalone also inhibited depolarization-secretion coupling with the same potency as alphaxalone. This results indicates that inhibition of depolarization-secretion coupling in nerve terminals is unlikely to play a major role in the production of anaesthesia.