Conduction in the cephalopod cardio-circulatory system and its neural control

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The paired auricles and systemic ventricle of the heart of octopus hummelincki were isolated together with the paired visceral nerves. Cut posteriorly to the first cardiac ganglion. Glass microelectrodes filled with 3M KCi were used to record intracellular myocardial potentials. Evoked in response to bathing in ACh or 5-HT (serotonin) solution. or by electrical stimulation of the visceral nerve.ACh induced hyperpolarization of ventricular muscle cells and bradycardia or cardiac arrest in beating hearts. Action potentials decreased in amplitude and duration during the AChhyperpolarization.On the other hand. 5-HT depolarized ventricular muscle cells and induced tachycardia in beating hearts. During a portion of the tachycardia. the action potentials increased in amplitude significantly.The intensity of nerve stimulation determined whether excitatory or inhibitory effects predominated. During nerve-induced tachycardia. There was an increase in rate of rise of the slow diastolic depolariza … More tion which preceded ventricular spike potentials. During nerve-induced bradycardia. or cardiac arrest. the membrane potential of ventricular muscle cells was hyperpolarzied beyond the maximum attained in a normal cardiac cycle.Both excitatory junctional plotentials (EJPs) and inhibitory junctional potentials (IJPs) were recordedfrom both auricular and ventricular myocardial cells. Pulses of electrical stimulation applied to the visceral nerve elicited EJPs or IJPs in a one-to-one ratio of stimulus to postjunctional potentials. It was discovered that the hyperpolarization or depolarization of myocardial membrane potential. in response to visceral nerve stimulation. resulted from summation of individual IJPs of EJPs.The presence of 5-HT and a peptide. CARP. was immunocytologically proved in the cardiovascular systems of a amphineuran. Liolophura; gastropods, Aplysia and Pleurobranchaea and a cephalopod. Octopus.5-HT produced excitatory effects on the systems. Effects of CARP on the systems remain to be examined. Less