Abstract
This work presents evidence that the atrial specific granule (ASG) is one of the intracellular calcium stores (ICaSs). First, a high calcium (Ca) concentration up to 81 mmol/kg dry wt. in ASG was determined by using an electron microscopic x-ray microanalysis technique. Second, Ca2+-ATPase was observed on the membranes of ASG and of the sarcoplasmic reticulum (SR) by using the cytochemical technique. Third, the activities of the Ca2+-ATPase on both the ASG membrane and on the SR memebrane were inhibited by 0.1 mM quercetin, but not by 0.1mM oligomycin. Because SR is an established ICaS, the similarities found in the present work between ASG and SR led us to postulate that ASG may be an ICaS in atrial cardiocytes, and that the Ca2+-ATPase on ASG membrane may pump Ca2+ from cytosol into ASG and thus play a role in maintaining the high Ca concentration in it.
