Tonic depolarization of excitatory nerve terminals in crayfish muscle by high concentrations of extracellular potassium.

At voltage-clamped fibres of the claw opener muscle of small crayfish, spontaneous quantal release of excitatory transmitter elicited by raising extracellular K+ to 100 mM was investigated. On application of the high K+ concentration, the rates of quantal release increased to n = 10,000-25,000 quanta/s within 10 s, and thereafter declined exponentially, either with a single (tau congruent to 15-40 s) or with two (tau 1 congruent to 15-40 s, tau 2 greater than 70 s) time constants. The total number of quanta released per trial ranged from s = 200,000 to 800,000 quanta. The results were derived by means of the fluctuation analysis technique.