Influences of glycine and neuron R14 on contraction of the anterior aorta of Aplysia.

Firing neuron R14 in the Aplysia parietovisceral ganglion enhances the force of stimulated contractions and causes rhythmic contractions rather than individual contractions in response to a single stimulation of the anterior aorta of Aplysia. Bath application of 1.0 mM glycine to the artery causes a small depolarization, rhythmic contractions and enhances the force of individual, neurally induced contractions of the anterior aorta. These observations suggest that the physiological role of the innervation of the anterior aorta by R14 is to convert the mode of contraction of the anterior aorta from direct neural control to a myogenic mode. R14 activity does not produce classical junction potentials and inotophoretically applied glycine does not produce detectable potential changes in the anterior aorta muscle fibers. Glycine increases the force and frequency of Aplysia heart beat, and blood pressure. Glycine causes release of preloaded Ca2+ from the ventricle of the Aplysia heart, implying that glycine causes intracellular release of Ca2+. The similarity of the actions of glycine and electrical activity in R14 extend previous evidence that R14 may utilize glycine to modulate the contractility of Aplysia circulatory muscle.