Cardiac pacemaker mechanisms in the ostracod crustacean XXXX .

@entity73 @entity1022 @entity71006 @entity4524
The heart of the ostracod crustacean @entity71006 has a single intrinsic neuron that morphologically appears to innervate the myocardium. We, therefore, examined the heart activity electrophysiologically to determine whether the heartbeat is neurogenic. Each heartbeat is associated with a myocardial action potential composed of a spike potential followed by a plateau potential. The frequency of the action potential is not stable but changes successively over a wide range. The action potential is not preceded by a pacemaker potential and has an inflection in its rising phase. The myocardial cells couple electrically and fire almost simultaneously. The frequency of the action potential was unchanged by injection of depolarizing or hyperpolarizing current into the myocardium. However, @entity73 potentials appeared during the depolarization and its frequency was higher with increasing current intensity. Application of 1-microM @entity1022 ( @entity4524 ) depolarized the myocardial membrane and completely prevented the action potential. During this depolarization, @entity73 potentials often appeared spontaneously. These results suggest that, although the myocardium has a property of conditional oscillator, the heartbeat is driven by the single cell cardiac ganglion that has both pacemaker and motor functions.
