A SUBPOPULATION OF INTRACARDIAC NEURONS FROM THE GUINEA-PIG HEART EXPRESSES SUBSTANCE-P BINDING-SITES

The distribution of binding sites for substance P labeled with [I-125] -Bolton-Hunter-reagent was studied in a mixed cell culture preparation from newborn guinea-pig atria and interatrial septum. A relatively sm all subpopulation of intracardiac neurons expressed substance P bindin g sites. These neurons exhibited a range of densities of labeling and could be heavily, moderately or lightly labeled with autoradiographic grains. In most cases, the autoradiographic grains were restricted to the neuronal cell body and more proximal regions of the neurites in cu lture. Intracardiac neurons expressing substance P binding sites were seen in close association with unlabeled neurons. The density of label ing and the distribution of autoradiographic grains over individual in tracardiac neurons did not appear to be related to whether they were m ono- or binucleate or their associated cell types. The possibility tha t the substance P binding sites demonstrated here represent functional receptors on intracardiac neurons and their potential role in the hea rt is discussed.