Stimulation by octopamine of the sodium efflux in barnacle muscle fibres

1. The behaviour of the ouabain-insensitive Na efflux in barnacle muscle fibres towards dl-octopamine has been investigated.2. It is found that these fibres are quite often sensitive to external application of octopamine. A concentration as low as 10⁻⁹ M is effective.3. The kinetic results indicate that the stimulatory response develops within 5–10 min of exposure of the fibre to octopamine and is transitory in nature.4. The response to octopamine is greater in size in the presence of l-isoamyl-3-isobutylxanthine (IAX) than in the presence of l-propyl-3-methyl-7-(5-hydroxyhexyl)-xanthine (PMX). But neither IAX nor PMX stops the response from decaying.5. The response to octopamine is highly dependent on the presence of external Ca²⁺.6. The provisional conclusion is that the barnacle muscle fibre may be a useful preparation for studying the hormonal function of octopamine.