STRETCH-INDUCED TRANSFORMATIONS IN MYOSIN EXPRESSION OF QUAIL ANTERIOR LATISSIMUS-DORSI MUSCLE

We have previously found alterations in expression of native myosin is oforms during adaptations to 30 d of stretch-induced hypertrophy in th e quail anterior latissimus dorsi muscle (ALD). However, myosin heavy and light chain expression have not been studied during adaptations to stretch. In the current study, expression of myosin heavy and light c hains and native myosin isoforms were characterized after placing a we ight on one wing of Japanese quail for 0, 7, 14, or 21 d (N = 8 birds . d(-1)). ALD muscle mass was significantly greater at days 14 (67.0 /- 4.4%) and 21 (70.2 +/- 4.0%) of stretch compared to day 7 (53.6 +/- 2.9%) of stretch. Native slow myosin-2 (SM2) expression increased fro m 43.1 +/- 1.7% in control muscles to 55 +/- 1.2% in stretch muscles, relative to the total myosin pool. The increase in native SM2 expressi on (similar to 12%) was observed at all three time points of stretch. In contrast, native slow myosin-1 (SM1) expression significantly decre ased from 34.1 +/- 1.7% in the control muscles to 24.6 +/- 1.2% in the stretch muscles, relative to the total myosin pool. There was an incr eased expression of slow heavy chain-two (SHC2) concurrent with a down regulation of the slow heavy chain-1 (SHC1). There was no change in th e relative percentages of either slow or fast myosin Light chains in o verloaded muscles at any of the time points following stretch. These r esults demonstrate that changes in myosin heavy chain expression, but not myosin Light chain expression accompany stretch-induced hypertroph y in the quail ALD.