[The effect of neostigmine and edrophonium on the MEPP frequency]

Edrophonium may have stronger effect on presynaptic site than neostigmine. Comparative study was done by measuring the miniature endplate potential (MEPP) frequency which reflect the presynaptic activity using rat phrenic nerve hemidiaphragm preparation. Preparations were placed in an organ bath, filled with Krebs solution and bubbled with 95% O2 and 5% CO2 at room temperature. A glass electrode filled with 3M KCL was inserted as close to the endplate as possible and 20 spots of MEPP were recorded for each drug. For recorded MEEP with amplification, frequency was analyzed with the signal processor. The highest effective level was different, being 10(-6)M in neostigmine and 10(-5)M in edrophonium. At these levels, MEPP frequencies of both drugs showed increases 2-4 times as high as the level in the control group and the degrees of increase were about the same with the two drugs. Our study revealed that both drugs have a strong effect on presynaptic sites and that these stimulating effects of edrophonium and neostigmine were about the same degree if 10 times as high a dosage as that of the former is used.