Distribution of synaptophysin immunoreactivity in guinea pig heart

The distribution of synaptophysin, an integral polypeptide of presynaptic vesicle membranes, was investigated in guinea pig heart by immunohistochemistry using monoclonal antibodies. Synaptophysin immunoreactivity was found in varicose nerve terminals in all regions of the heart. Dense networks of immunoreactive varicosities were found to surround the vasculature and to be located within the subendocardial layers of the atria and ventricles, the highest levels being seen in the innervation of the conductive system. As synaptophysin is probably a component of the presynaptic vesicles of all synapses, its use as a marker of all nerve terminals within the heart is proposed.