Fig. 6. Quantitation of costameric organization in K19^–/– myofibers. Longitudinal sections tangential to the sarcolemma of myofibers were labeled with antibodies against βI-spectrin, and costameres were scored as extensively disrupted (category 1, panel 1; see also Fig. 5D,G), moderately disrupted, with only one set of costameric domains remaining (category 2, panel 2), or normal, with costameres present over Z- and M-lines and oriented longitudinally as well (category 3, panel 3; see also Fig. 5A). Costameres in the K19^–/– fibers (gray bars) were significantly more disrupted than in controls (striped bars; see text).