Abstract
1. In the nerve—muscle preparation, where catch was characteristically minimal, 5-hydroxytryptamine (5-HT) had no effect on resting membrane potential, junction potentials, spikes or contraction.
2. In muscle bundles, where catch was prominent, 5-HT did not change membrane potentials, but prolonged junction potentials and lowered the threshold for spike discharge and contraction.
3. In muscle bundles, exposed to high concentrations of 5-HT, depolarization evoked repetitive spikes, while in low 5-HT, spikes were seldom fired even with much greater depolarization.
4. In muscle bundles, the effective membrane resistance, Reff., decreased from 45-60 to 23-35 MΩ as 5-HT concentration was increased.
5. It is suggested that 5-HT may facilitate spike discharge by lowering the internal free Ca2+ concentration.
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Selected References
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