Figure 2. Electrophoretic (A) and immunohistochemical (B) characterization of single human jaw-muscle fibers obtained from the digastric and temporalis. Consecutive fibers (1–5) were immunolabeled with antibodies against MyHC-IIA+IIX, MyHC-IIA, and MyHC-I. MyHC composition of fragments of the same fibers was determined by gel electrophoresis. Fiber types are: pure type I (1), pure type IIA (4), pure type IIX (5), and hybrid type IIA+IIX (2 and 3). In a total 218 fibers, 118 were classified as pure and 100 as hybrid fibers. In the hybrid fibers, all combinations of isoforms were found; the proportions of these isoforms varied greatly (for more details, see Korfage and Van Eijden, 2003b).