ULTRASTRUCTURE OF SARCOPLASMIC-RETICULUM IN ATRIAL MYOCARDIUM OF PATIENTS WITH MITRAL VALVULAR DISEASE

Abstract

Alterations observed in the sarcoplasmic reticulum of muscle cells in left and right atrial myocardium from 10 patients with mitral valvular disease consisted of: proliferation of rough-surfaced endoplasmic reticulum, which formed large cisterns in perinuclear areas of hypertrophied cells and was considered indicative of increased protein synthesis; proliferation of free sarcoplasmic reticulum (SR), a change that occurred in degenerated cells and appeared to be related to loss of contractile elements; 2 types of aggregates of tubules of free SR.cntdot.1 type was associated with abnormal Z-band material and was found only in cells showing loww of myofibrils and proliferation of free SR, whereas the other was not associated with either of these changes and occurred in less severely altered cells; and proliferation and enlargement of cisterns of extended junctional sarcoplasmic reticulum, which formed 2 distinct types of complexes (the 1st of these consisted of large, convoluted (Type A) cisterns that were wide (550-650 .ANG. in thickness) and did not have a central dense lamina; the 2nd was composed of stacks of concentric or parallel (Type B) cisterns that were narrower (220-300 .ANG. in thickness), had a central dense lamina and were separated from one another by layers of glycogen granules). The formation of these complexes of cisterns was regarded as an extreme form of overdevelopment of extended junctional sarcoplasmic reticulum in atrial muscle cells.