STRETCH INDUCES NONUNIFORM ISOMYOSIN EXPRESSION IN THE QUAIL ANTERIORLATISSIMUS-DORSI MUSCLE

Stretch-overload has been shown to elevate muscle mass in the avian an terior latissimus dorsi (ALD) by increasing both fiber size and fiber number; however, it is not known if these adaptations result in unifor m regulation of myosin isoform expression along the length of the fibe rs in this slow tonic muscle. When a weight was added to the left wing of 20 adult quail for 30 days, ALD mass was increased by 161%. ALDs w ere divided into proximal, middle, and distal portions. Tissue cross-s ections from each muscle portion were reacted against monoclonal antib odies for either fast (FM) or slow myosin (SM), or processed for ident ification of native myosin isoforms. The number of fibers expressing F M increased by 190% in the distal region after stretch; however, most of these were small fibers. Electrophoretic analyses of stretched musc les demonstrated an upregulation of SM2 in all regions of the ALD. SM1 was only down-regulated in the proximal region of the ALD. FM isoform s had greater increases in the proximal region than other regions of t he overloaded ALD. These data indicate that stretch-induced hypertroph y induces a non-uniform increase in fast myosin isoforms and SM1 along the length of the fibers of the ALD. (C) 1993 Wiley-Liss, Inc.