I-band periodicity in rabbit psoas muscle fibers measured using digital image-analysis techniques.

The fine periodicity of I-band was measured in single fibers of glycerinated rabbit psoas muscle, in relaxed, activated and rigor states at short (2.5 microns) and long (3.2 microns) sarcomere lengths. Measurements were carried out using fast Fourier transforms obtained from I-band regions of digitized electron micrographic images. The mean periodicity, averaged among all conditions, was 42.5 +/- 1.5 nm. Some differences were found among the different conditions, but they were too small to be conclusive. The observed periodicity value was considerably higher than the generally assumed value of 38.5 nm, and is surprisingly close to the myosin-repeat spacing.