Age-related changes of elements in the human sinoatrial nodes

Introduction To elucidate compositional changes of the sinoatrial node (SAN) with aging, the authors investigated age-related changes of elements in the SANs of Thai subjects with a wide range of ages. Materials and methods The Thai subjects consisted of 37 men and 36 women, ranging in age from 35 to 91 years (average age=67.713.3 years). The samples of the SANs were obtained by dissecting the tissue perpendicular to the terminal crest. After incinerating with nitric acid and perchloric acid, element contents were determined by inductively coupled plasma-atomic emission spectrometry. Results Although the P content tended to decrease in the SANs with aging, there were no significant correlations between age and seven element contents, such as Ca, P, S, Mg, Zn, Fe, and Na, in the SANs. However, on the examination separated into the men and women’s SANs, a significant inverse correlation was found between age and P content only in the men’s SANs, but it was not found in the women’s ones. Conclusion The P content of tissue is mostly determined by the nucleic acid content (DNA and RNA) and the phospholipid content of the tissue. Nucleic acids in the cell nucleus and the cytosol and phospholipids in the cell membrane are indicators of metabolically active cells. Taking into consideration, it is reasonable to presume that the P content indicates the active cell density in the SAN, i.e. the number of active cells per volume. Therefore, there is a possibility that the active cell density of the SAN decreases significantly in men with aging. Regarding the relationships among elements, extremely or very significant direct correlations were found among the Ca, P, S, and Mg contents in the SANs.