CAN BARIUMSUPPORTTHERELEASE OFACETYLCHOLINEBYNERVEIMPULSES

techniques were used tostudy theeffects ofBaon therelease ofacetylcholine (ACh)fromfrogmotornerve terminals. Equimolar substitution ofBaforCaeliminated end-plate potentials (e.p.ps) without acorresponding decline intheamplitude ofthenerveterminal action potential. Miniature endplate potentials (m.e.p.ps) were readily detectable inBa solutions despite a depolarized musclemembrane. Studies on thee.p.pincurarized preparations bathed withdifferent concentrations ofCaandBasuggest that Ba may competewithCa intheprocessbywhich depolarization ofthenerveterminal leads totherelease ofACh.Repetitive nervestimulation at 1 Hz inBa solutions caused5-20 foldincreases in m.e.p.p frequencies (7experiments). Stimulation ofBa-bathed preparations at 1OHzelevated m.e.p.pfrequencies to veryhighlevels thatcould notbemeasured accurately (,100/s). Itissuggested that theasynchronous discharge ofm.e.p.psproduced byrepetitive nervestimulation is theelectrophysiological correlate oftheevoked AChoutflowinBasolutions detected previously bybioassay of theperfusion fluid.