Neurohormonal Modulation of the Cardiac Outflow through the Cardioarterial Valve in the Lobster

1. Systolic pressure in the abdominal artery of the lobster Panulirus japonicus (Von Siebold) was decreased by contraction of the cardioarterial valve located at the posterior exit of the heart. Crustacean neurohormones, octopamine and proctolin, induced rhythmic contractions or contracture of the posterior valve but serotonin did not induce valve contracture. 2. Systolic pressure in the posterior artery was reduced when the anterior cardioarterial valves contracted at the same time as the posterior valve. Proctolin caused the anterior and posterior valves to contract. Octopamine caused only the posterior valve to contract and often caused the anterior valves to relax. 3. Proctolin induced depolarizing responses while serotonin often induced hyperpolarizing responses in muscle cells of the anterior and posterior valves. Octopamine hyperpolarized the resting membrane potential of muscle cells in the anterior valves and depolarized the membrane potential in the posterior valve. 4. In some intracellular recordings from the valve muscle cells, slow action potentials followed by a plateau were produced on slow sustained depolarization induced by proctolin or octopamine. The action potential was followed by a large contraction of the valve. Contracture of the valve was associated with a large sustained depolarization in single muscle cells of the valve.