Pacemaker activity in the heart of a beetle, allomyrina dichotomus

1. 1. The heartbeat of an adult beetle, Allomyrina, initiates from the rear portion of the heart, the impulse propagating forward, however, sometimes generating from the anterior region, and taking a reversed direction. 2. 2. The heart is considered to be myogenic, because of the absence of neural deflection in the recorded action potential, the presence of typical slow diastolic depolarization and also that of spontaneity even in a small fragment of the heart. 3. 3. Between connected fragments, there is often an interaction which shortens or lengthens each beat interval, according to the action potential during the beating cycle of the other. 4. 4. The interaction shows a phase-response curve, and the same phenomenon is also revealed by electric stimulation. 5. 5. The rhythm of the heartbeat is suggested to be formed by integrative interaction among contiguous spontaneous myocardia.