ATRIAL SPECIFIC GRANULES - AN INTRACELLULAR CALCIUM STORE

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, C a2+-ATPase was observed on the membranes of ASG and of the sarcoplasmi c reticulum (SR) by using the cytochemical technique. Third, the activ ities of the Ca2+-ATPase on both the ASG membrane and on the SR memebr ane were inhibited by 0.1 mM quercetin, but not by 0.1 mM oligomycin. Because SR is an established ICaS, the similarities found in the prese nt 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 p ump Ca2+ from cytosol into ASG and thus play a role in maintaining the high Ca concentration in it.