Effects of goniopora toxin on bullfrog atrial muscle are frequency-dependent

Mami Noda, Ikunobu Muramatsu, Motohatsu Fujiwara, Katsuro Ashida

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6 Citations (Scopus)


When goniopora toxin (GPT), a marine toxin isolated from coral, was applied to the bullfrog atrial muscle, the duration of action potential (APD) was prolonged, and a positive inotropic effect was produced. Such effects of GPT were influenced by stimulus frequency. At lower frequencies of 0.1 Hz, GPT (10 to 100 nmol/l) produced a moderate prolongation of APD and positive inotropic effect. At higher prequencies (1.0 Hz), however, the effects of GPT on both APD and contraction were suppressed. In contrast, APD and duration of contraction were prolonged with long intervals of stimulation (1-3 min), in the presence of GPT. The rested-state contraction was also markedly increased and prolonged by GPT. When the membrane potential was conditioned by voltage clamp pulses, the prolonged action potential in GPT-treated muscle was shortened in proportion to the increase in conditioning depolarization. However, the shortening effect of conditioning depolarization was attenuated by lengthening the resting period after the conditioning depolarization. These results, in conjunction with our previous results, suggest that the frequency-dependent effects of GPT on APD and contraction reflect time-and membrane potential-dependent changes of the toxin-modified sodium channels.

Original languageEnglish
Pages (from-to)59-66
Number of pages8
JournalNaunyn-Schmiedeberg's Archives of Pharmacology
Issue number1
Publication statusPublished - Jul 1985
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Pharmacology


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