The effects of monoamines on tarantula skeletal muscle.

1. The effects of various monoamines (dopamine, epinephrine, octopamine and 5-hydroxytryptamine) on the contractility of tarantula leg muscle were measured.2. All monoamines resulted in increases in the apmlitude of nerve-evoked muscle contraction.3. The presence of cAMP in tarantula muscle was confirmed and the concentration of cAMP found to increase with the application of monoamines.4. Dibutyryl cAMP caused an increase in contraction amplitude similar to that observed with monoamines.5. It is concluded that monoamines do affect muscle contractility in the tarantula. The possibility of additional modulatory mechanisms was not eliminated.