Neuromuscular Facilitation in Crayfish: Dependence on Potassium and Strophanthidin

1. Long-term facilitation (LTF) and short-term facilitation (STF) at excitatory neuromuscular junctions were studied under conditions of varying [K+]0 and with the addition of strophanthidin. 2. The magnitude of LTF varied inversely with [K+]0, while STF was unaffected. 3. Strophanthidin concentrations greater than 10−5 M greatly increased LTF, but not STF. 4. Both LTF and STF were unaffected by large decreases in excitatory junctional potential amplitude produced by the addition of GABA or Mn+2. 5. The results support the hypothesis that LTF is a consequence of Na+ accumulation in presynaptic terminals and behaves independently of STF.