Electrophysiological Investigations of the Heart of Squilla Mantis

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Abstract
1. There was a seasonal variation in the strength of the effect which extracts of the pericardial organs of Squilla mantis exert on the animal's heart. The extract was most effective in the spring and summer. 2. An investigation was made of the way in which the pericardial organ extract acts at a cellular level to increase the amplitude and frequency of the heart beat. 3. The extract did not affect the rate of impulse firing within the ganglionic nerve trunk burst. It increased the ratio of the number of impulses per burst: burst interval. 4. It initiated burst firing in complete g.n.t.'s which had become quiescent, and in those which had previously given only one impulse in response to an applied stimulus. 5. The junction potentials recorded intracellularly from Squilla heart muscle increased in height on adding pericardial extract. Some of this increase resulted from facilitation of the junction potentials at the increased heart rate, but 10-20% of the increase was rate-independent. 6. These results suggest that the extract acts at a minimum of two primary sites within the heart.

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