ANNEXIN-V IN THE ADULT-RAT HEART - ISOLATION, LOCALIZATION AND QUANTITATION

Annexins are a family of proteins with calcium- and phospholipid-bindi ng properties, The present study was performed to identify which membe rs of the annexin family are present in rat heart and to determine the cellular and subcellular distribution of annexin V, the most prominen t annexin in rat cardiac tissue, in isolated ventricular myocytes and cultured endothelial and fibroblast-like cells. The presence of annexi n I plus II, Iii, TV, V and VI in rat cardiac tissue was positively es tablished with western blot analysis. Immunohistochemistry acid wester n blot analysis revealed that annexin V is present in both cardiomyocy tes and non-myocytal cells of the heart, In endothelial cells and fibr oblast-like cells annexin V is predominantly localized in the cytoplas m and in cardiac myocytes in close vicinity of the sarcolemma, This la st finding is confirmed by electron microscopy. Northern blot analysis demonstrated that all cell types investigated showed expression of an nexin V. Annexin V mRNA levels were highest in the fibroblast-like cel ls, followed by the endothelial cells, and a weak signal was observed in the cardiomyocytes. By means of a sandwich-type enzyme-linked immun osorbent assay (ELISA) annexin V content, in intact adult rat heart, i solated myocytes, cultured cardiac endothelial cells and fibroblast-li ke cells was found to be 0.70, 0.17, 1.63 and 3.84 mu g/mg total prote in, respectively. The differences in subcellular localization of annex in V in myocytes and non-myocytes suggest differences in biological fu nction of annexin V in the various cell types.