Introduction
We have previously cloned and characterized a novel hormone from the salmon (Salmo salar) which has a uniquely heart-specific distribution and has low structural similarity with any other known natriuretic peptide (Tervonen et al. 1998). The release of salmon cardiac peptide from heart ventricle in vitro responds to a mechanical load (Kokkonen et al. 2000). Here we report the localization of sCP in the salmon heart.
Methods
Immunohistochemistry, (Avidin-Biotin-peroxidase), electron microscopy, immunoelectron microscopy (protein A-gold), and specific radioimmunoassay.
Results
The sCP antiserum did not crossreact with rat ANP, porcine BNP, rat CNP, eel ANP, and rainbow trout VNP. Both atrial and ventricular myocytes of the salmon stained immunohistochemically. In the atrium, the immunostaining was stronger near the nucleus than elsewhere in the sarcoplasm but it was more uniformly distributed in the ventricle. Small granules with a diameter of 100 nm to 200 nm were found in the sarcoplasm. The granules were located near the nucleus, near the Golgi apparatus, between myofilament bundles, and in subsarcolemmal positions. The granules had an electron dense core with a halo. Gold particles, conjugated to the antibodies raised against sCP, were deposited on the granules found in transmission electron microscopy. A significantly (P < 0.05) higher concentration of sCP was found in atrium than in the ventricle, 16.2 (SEM 3.5) pmol/mg tissue (n=8) and 4.5 (SEM 1.7) pmol/mg tissue (n=8), respectively.
Conclusions
Salmon cardiac peptide is localized in secretory granules in salmon heart. The morphology of the granules support the notion that both the atrium and the ventricle utilize the regulatory pathway to release the salmon cardiac peptide.
References
Kokkonen, K., Vierimaa, H., Bergström, S., Tervonen, V., Arjamaa, O., Ruskoaho, H., Järvilehto, M. & Vuolteenaho, O. Am J Physiol 278, E285-E292
Tervonen, V., Arjamaa, O., Kokkonen, K., Ruskoaho, H. & Vuolteenaho, O. 1998. Endocrinology 139, 4021-4025