Occurrence of Z-band widening in human atrial cells

Fifty-four biopsies of human auricular appendages have been studied under the electron microscope. In 24% of the cases, various degrees of broadening of the Z-lines were observed. There was a relation between the changes of the Z-line, the age of the patient, and the surgical diagnosis. The structures observed in the Z-disc had a diameter corresponding to that of the I-band filaments and appeared to be in continuity with them. These periodic structures were oriented parallel to the long axis of the fiber, but in one case they were oblique. The reported anomalies of the Z-line do not correspond exactly to those previously described in cats and dogs, nor to the rods of the "nemaline myopathy." The present findings cannot be explained by the existing theories on the structural organization of the Z-line.