Immunohistochemical Demonstration of Leu‐7 (HNK‐1), Neurone‐Specific Enolase (NSE) and Protein‐Gene Peptide (PGP) 9.5 in the Developing Camel (Camelus dromedarius) Heart

The development of the heart‐conducting system has been controversially discussed. The common opinion that these specialized myocytes originate from mesodermal precursors has been challenged when nerve‐specific antigens (Leu‐7, NF, G1N2) were demonstrated in embryonic hearts of various species, suggesting a neural crest contribution to the embryonic conducting tissue. Anti‐Leu‐7 (HNK‐1) antibodies were reported to reliably mark the conducting system in developing rat, chicken and human hearts. The present investigation was carried out on the hearts of 15 camel fetuses at 35, 45, 60, 75 and 100 cm crown‐rump length (three specimens for each stage), in addition to three adult hearts. We investigated the antigenicity of cardiac structures for Leu‐7, NSE (Neurone specific Enolase) and PGP (Protein Gene Peptide) 9.5. In all specimens investigated, both NSE and PGP 9.5 were expressed by cardiac nerves and conducting system components. The sinuatrial and atrioventricular nodes, the atrioventricular bundle as well as subendocardial and intramyocardial Purkinje fibers were stained. In contrast, the developing conducting system did not react with anti‐Leu‐7 antibody, although Leu‐7 antigenicity was strongly expressed by the developing cardiac nerves. In adult camel hearts, the same pattern of immunoreactivity for the markers studied was still retained. Our results show that the expression of marker proteins for the developing conducting system is species‐specific. Therefore, these markers are of little significance in discussions on the possible neurogenic nature of the heart conducting tissue.