Rough endoplasmic reticulum in the adult mammalian cardiac muscle cell.

The morphology, distribution and extent of rough endoplasmic reticulum (RER) was investigated in normal and ischaemic left ventricular 'working' myocytes of the adult rabbit. Continuity of RER with membranes of the Golgi apparatus, nuclear envelope and sarcoplasmic reticulum (SR) is documented, though 48% of RER profiles appear as discrete entities in the interfibrillar and perinuclear sarcoplasm. Of the RER intercalated in the SR, 31% of the segments occur adjacent to the Z-tubule, 15% in longitudinal elements of free SR and 5% adjacent to junctional SR. Quantitative analysis of profile lengths shows the RER to be more extensive than hitherto suspected, with 73% of profiles having lengths in excess of 200 nm and some (albeit uncommonly) in excess of 8 micron.