Abstract

Contractile and metabolic activities of the isolated heart of Panulirus japonicus were recorded while thermal and hormonal stimuli were applied for 3–6 min. The heart beat was often augmented in amplitude with a fall in temperature from 20° to 17–15°C. With the augmented beat, a decrease of pO₂ in the ventricle indicated an increase in oxygen consumption rate of the heart. When serotonin (0.1 µM) and the cold stimulation were applied at the same time, pO₂ in the ventricle decreased, suggesting that the metabolic rate of the heart markedly rose. In contrast, octopamine (1 µM) raised the oxygen consumption rate of the heart only slightly. Octopamine greatly enhanced the membrane excitability and contraction force of the heart during cold treatment. A transient period of cooling in vivo may cause the pericardial organs to release octopamine and serotonin in P. japonicus. This may be relevant to the care of spiny lobsters during mariculture, capture, handling and transport.