Erspamer G F, Severini C
Arch Int Pharmacodyn Ther. 1987 Feb;285(2):324-34.
Extracts of the skin of the Australian frog Pseudophryne coriacea (PS) displayed a striking potentiating effect on contractions evoked in the isolated frog rectus abdominis muscle by direct electrical stimulation. There was both a conspicuous increase in twitch amplitude and a remarkable prolongation of twitch duration. High concentrations of PS also elicited an increase in tone. The effect on twitch was mainly due to direct stimulation of muscle fibres, the effect on tone to facilitation of acetylcholine release from the motor nerve terminals embedded in the musculature. Unlike the first effect, the second was blocked by tubocurarine and alpha-bungarotoxin. Tetrodotoxin inhibited both the basal and PS-stimulated twitch. Experiments with EGTA, a calcium chelating agent, suggest that activation of voltage-dependent calcium channels is involved in the response of the frog muscle to PS. Low concentrations of PS were ineffective on the non-stimulated muscle; high concentrations, on the contrary, generally caused an increase in tone. This was completely inhibited by the blockers of the nicotinic acetylcholine receptors, again suggesting a transmitter release from the nerve terminals.
澳大利亚蛙皮氏拟蟾（PS）的提取物对直接电刺激离体蛙腹直肌所诱发的收缩表现出显著的增强作用。抽搐幅度明显增加，抽搐持续时间显著延长。高浓度的PS还能引起张力增加。对抽搐的影响主要是由于对肌肉纤维的直接刺激，对张力的影响则是促进了嵌入肌肉组织中的运动神经末梢释放乙酰胆碱。与第一种效应不同，第二种效应被筒箭毒碱和α-银环蛇毒素阻断。河豚毒素抑制基础抽搐和PS刺激的抽搐。用钙螯合剂乙二醇双（2-氨基乙基醚）四乙酸（EGTA）进行的实验表明，电压依赖性钙通道的激活参与了蛙肌肉对PS的反应。低浓度的PS对未受刺激的肌肉无效；相反，高浓度通常会导致张力增加。这被烟碱型乙酰胆碱受体阻滞剂完全抑制，再次表明是神经末梢释放了递质。
