The Effects of Osmoregulatory Solutes On Tension Generation by Dogfish Skinned Muscle Fibres

Abstract

Many marine organisms accumulate high concentrations of solutes in their tissues to maintain osmotic balance. Osmoregulatory solutes are usually end-products of metabolism rather than inorganic ions (Prosser, 1973). For example, skeletal muscle from marine elasmobranchs, holocephalans and the coelacanth contains high concentrations of both urea (300–600 mm) and methylamine compounds, such as trimethylamine oxide (175–250 mm) (Pang, Griffith & Atz, 1977). Urea is a potent protein destabilizer, and most elasmobranch enzymes examined are inhibited by urea (Yancey, 1978). However, it has recently been found that TMAO acts as a general protein stabilizer and can offset the effects of urea on enzyme Km and maximal velocity in vitro (Yancey & Somero, 1979, 1980).