Electron Microscopic Autoradiographic Study on the Secretion of Atrial Specific Granules from Atrial Cardiocytes in Dehydrated Rats

Shin, Hae Young; Song, Chang Ho; Kim, Hyoung Tae; Han, Eui Hyeog; Lim, Jae Won; Lee, Moo Sam

Abstract

This study was performed to investigate for the effect of dehydration on the synthesis, secretion and secreted pathway of atrial specific granules contained ANP by electron microscopic autoradiography. Male Sprague-Dawley rats, body weigh of about 50 g (range 47 to 53 g), were divided into control, 1 day dehydration and 3 days dehydration groups. Each group was divided into four groups according to sacrificed time on 20 min, 60 min and 240 min after the injection of L-leucine 3 H. Tissues of the right atrium obtained from animals were processed for typical electron microscopic procedure, and then embedded in Epon 812. Ultrathin sections were followed for electron microscopic autoradiographic method. Atrial specific granules were various in size, and some granules had a lower electron densities and indistinct granular membrane in the dehydration groups compared with the control group. In the electron microscopic autoradiographs of atrial wall, silver grains indicated by means of the positions of labelled L-leucine 3 H over the cell inclusion included atrial specific granules, cell organelles, intercellular spaces and blood vesseles. In the control group, high specific radioactivity was observed in the Golgi apparatus at 20 min, and in the rough endoplasmic reticulums and atrial specific granules at 60 min after the injection of L-leucine3H. And high level of radioactivities were observed in the cell membranes and blood vesseles at 240 min after the injection of L-leucine3H. In the 1 day and 3 days dehydration groups, radioactivities of Golgi apparatus, atrial specific granules, cell membranes and intercellular spaces were high level at 20 min, and radioactivities of rough endoplasmic reticulums and blood vesseles were high level at 60 min after isotope injection. Stored atrial specific granules were increased to 34.1% in the 1 day dehydration group, 27.4% in the 3 days dehydration group compared with the control group. In the 3 days dehydration group, newly formed granules increased 85.02% at 20 min, but those decreased rapidly to 36.87% at 60 min, 20.45% at 240 min after the injection of L-leucine3H in atrial cardiocytes. This results suggest that total ANP increased rapidly in the atrial cardiocytes, and newly formed ANP secreted rapidly into the intercellular space in the condition of dehydration, and ANP from atrial cardiocytes remain in intercellular space for dehydration period.