Pharmacological control of muscular activity in the sea urchin larva—IV. Effects of monoamines and adenosine

Abstract

1. The muscular activity of the sea urchin pluteus is affected by catecholamines. α-Agonists in high concentrations bring about a strong, temporary, stimulation. 2. The stimulation by β-agonists tends to be masked by different mechanisms. 3. Serotonin brings about a strong stimulation of long duration, even at 10 −7M.It reactivates larvae where the activity has declined after exposure to catecholamines. A dopamine-effect at 10 −5−5 × 10 −6M is similar to that of serotonin. The effect of adenosine is similar to that of dc-c-AMP. 4. The action of the α-and β-agonists and adenosine appears to involve an increased respectively excessive Ca 2+-influx, directly or indirectly mediated by c-AMP. 5. It is suggested that a strong Ca 2+-influx induces an outflux of K + leading to hyperpolarization. Serotonin may decrease the K +-outflux.