Hemoglobin absorption by proximal tubule cells of the rabbit kidney. A study by electron microscopic autoradiography

Hemoglobin absorption in proximal tubule cells of the rabbit kidney was studied by means of combined autoradiography and electron microscopy and using radioisotope-labeled hemoglobin. The hemoglobin was labeled with tritiated dl-leucine during in vitro synthesis of hemoglobin by rabbit reticulocytes and injected intravenously in small amounts. The bulk of the labeled hemoglobin, after 150 minutes, is located in specific cytoplasmic bodies in the proximal tubule cells. Of all grains observed, 63.4 % lay directly over three varities of the type II cytoplasmic bodies. Of the remaining grains, the majority lay within 0.4 μ of the limiting membrane of these cytoplasmic bodies. Totally, approximately 85 % of all grains were found over or immediately adjacent to the type II cytoplasmic bodies. A small percentage of grains was found in apical vacuoles containing little or no electron dense material. This and other observations indicate that electron dense material in sections of proximal tubule cells during hemoglobinuria cannot be specifically equated with the presence or absence of hemoglobin.