Effect of lithium on veratridine-induced quantal and non-quantal release from inhibitory nerve terminals in crayfish muscle.

Muscle fibres of small crayfish were voltage clamped and superfused for about 10 min with Li+ saline (Na+ replaced by Li+) which contained 5 mmol/l glutamate to desensitize excitatory postsynaptic receptors. Then 100 mumol/l veratridine were added to the superfusate which caused strong asynchronous quantal release of inhibitory transmitter. However, in the presence of Li+ strong inhibitory quantal release was only transient. It could be activated a second time by removal of Li+ and readministration of Na+. From the total of 0.7 to 1.1 million quanta released by veratridine only about 30-35% could be released in Li+ saline. The voltage clamp DC-currents recorded during veratridine-induced quantal release suggested that a non-quantal release component is additionally involved. This non-quantal release component was most prominent during the period of quantal release in Li+ superfusate while it was less obvious during the second enhancement of quantal release in normal saline. Together with previous results (Martin and Finger 1988) it may be concluded that quantal release, but not non-quantal release, is decreased by Li+ in the nerve terminals.