Meeting Abstract

60.11  Tuesday, Jan. 6  Does urea affect the calcium binding properties of parvalbumin and thereby alter muscle relaxation in trout? COUGHLIN, D.J.; Widener University, Chester, PA djcoughlin@widener.edu

Parvalbumin (PV), a myoplasmic protein with multiple isoforms in fish muscle, is a low molecular weight protein (9-11 kD) that appears to aid in relaxation from contraction. PV binds free Ca²⁺, which reduces the intracellular concentration of the ion and leads to muscle relaxation. The impact of PV on muscle relaxation depends on both the rate of Mg²⁺ dissociation as well as the rate of Ca²⁺ binding. Work in elasmobranchs has shown that the binding properties of some isoforms of PV are labile to physiological concentrations of urea. For instance, marine elasmobranchs can have concentrations of urea in their tissues on the order of 200-300 mM. At such concentrations, urea reportedly leads to increased binding affinity of PV for Ca²⁺ (lower Ca²⁺ K_D). We tested this hypothesis by manipulating urea content of muscle in mechanics experiments. Using rainbow trout as the experimental subject, contractile properties were measured in white, fast-twitch muscle bundles in physiological saline containing zero, 200 and 400 mM urea. The time for muscle bundles to relax from contraction decreases with increasing urea content. Further, the effect is reversible lowering urea content leads to longer muscle relaxation times. These preliminary experiments suggest urea content influences muscle relaxation, perhaps by altering the binding properties of PV, and may therefore affect swimming behavior in some fishes.