EFFECT OF CONTROLLABLE STRESS ON MYOSIN HEAVY-CHAIN EXPRESSION AND MUSCLE-SPECIFIC PROTECTION BY CLOMIPRAMINE

This study evaluated the influence of a controllable and painless stre ss, conditioned bright-light active-avoidance, on the expression of my osin heavy chain (MHC) protein isoforms in two nape and three masticat ory rat muscles: longissimus capitis (L), rectus capitis dorsalis majo r (R), anterior digastric (AD), anterior temporalis (AT) and masseter superficialis (MS). The effects of a concomitant antidepressant treatm ent with clomipramine (CMI) on the muscle structure were also investig ated. The three adult fast MHC isoforms were detected in all muscles s tudied: MHC 2A, 2X and 2B. The AT structure was not significantly modi fied by stress either under saline or under CMI treatment. In the othe r muscles studied, the stress situation induced a marked increase in t he relative expression of MHC 2B and a decrease in MHCs 2X and 2A, exc ept in L in which the MHC 2A decrease did not reach a statistically si gnificant level. Under controllable stress, the CMI treatment led to t he same MHC profile in AT, L, R and AD as saline, except in L where th e MHC 2X decrease was no longer statistically significant. However, in MS, under controllable stress and CMI treatment, the MHC distribution was significantly different from the stressed saline-treated group an d became comparable to the control again. MHC 2B has a higher shorteni ng velocity than MHC 2X, which has a higher one than MHC 2A. According to total MHC isoform expression, the controllable stress-induced tran sformations would thus lead to increased velocity of all five muscles studied except in AT. This latter seems, therefore, not very sensitive to environmental requirements. Our results indicate that controllable stress produces important changes in the contractile properties of na pe and masticatory muscles. Furthermore, this study demonstrates the p rotective effect of CMI against muscle structure transformations induc ed by controllable stress in MS, and that these effects are muscle typ e-specific. (C) Kluwer Academic Publishers.