VILLARIN, J.J.*; SCHAEFFER, P.J.; CARLSEN, R.C.; Univ. of California, Davis; Washington Univ School of Medicine; Univ. of California, Davis: Non-Contractile Functions in Skeletal Muscle: Adaptation and Interactions

Vertebrate skeletal muscle is most often discussed in the context of contractile function, which provides a broad range of functions: locomotion, breathing, posture, feeding, sound production, and so on. Contractile properties of muscle have been convincingly shown to demonstrate adaptive plasticity when faced with altered demand. Here, we aim to extend discussion of skeletal muscle plasticity beyond the seemingly principle function of force production to the role of adaptation in the diverse non-contractile functions. Given that many of the structures involved in non-contractile functions are also involved in contraction and force production, it follows that plasticity should extend to these other functions as well. Further, the structural components responsible for individual functions may not be unique to that single role; thus giving rise to interaction. The resulting cross-adaptations may result in either beneficial or detrimental outcomes. The dominating effect is a function of the adaptive potential of the particular system along with the magnitude of the stimulus driving the relative adaptive responses. Three systems have been selected to illustrate this principle: thermogenesis, electrolyte homeostasis, and substrate flow (e.g. muscle catabolism feeding into injury-induced amino acid flow). For example, the drive towards increased thermogenic capacity in skeletal muscle influences the ability of those same muscles to perform locomotory tasks, and in some instances influences the ability to regulate ion gradients. Thus the plastic nature of skeletal muscle in response to altered functional demand affects numerous systems. Further, interactions between functional systems can lead to unexpected cross adaptation.