Autoradiographic demonstration of hemoglobin in lysosomes of rabbit proximal tubule cells during experimental hemoglobinemia

The ultrastructural location of acid phosphatase in rabbit proximal tubule cells following intravenous injection of 3H-labeled or unlabeled homologous hemoglobin was investigated. Cytoplasmic bodies which were limited by a single triple-layered membrane about 90 Å in thickness (cytoplasmic bodies type II) were acid phosphatase-positive and are interpreted to be lysosomes. Cytoplasmic bodies limited by a single triple-layered membrane about 65 Å thick (cytoplasmic bodies type I, “microbodies”) did not contain acid phosphatase. To reveal simultaneously the location of radioactive homologous hemoglobin and acid phosphatase, kidney tissue was first incubated in a Gomori medium for acid phosphatase and then analyzed by electron microscopic autoradiography. The observations showed that the bulk of the absorbed radioactive hemoglobin was located in acid phosphatase-containing cytoplasmic bodies type II (lysosomes). Hemoglobin was not observed in any cytoplasmic bodies which were acid phosphatase negative. It is probable that the absorbed hemoglobin is degraded in some of the lysosomes in which it has been segregated. Comparisons with previous protein absorption studies suggest that the cellular and lysosomal handling of absorbed protein depends on which protein is absorbed, as well as on the amount taken up.