The effect of serum albumin on the efflux of K42 from frog sartorius muscle

The effect of serum albumin on the washout of K42 from isolated frog sartorius muscles, previously labeled in vitro with this isotope, has been investigated. Incorporation of 1% serum albumin in the washout fluid has been found to cause a significant reduction in the rate constant for K42 loss from the muscle fibers. A similar reduction in the rat constant for K42 efflux was observed when the medium, though not containing protein, was exhaustively dialyzed before use against a solution containing serum albumin. Addition of 10−6 M HgCl2 to “dialyzed” Ringer increased the rate of loss of K42 from the fibers. Effects similar to those obtained with serum albumin were observed when 10−4 M cysteine was incorporated in the washout fluid. 3‐mercapto‐propanol gave rise to transient reductions in the rate of K42 efflux, but, following prolonged exposure to this agent, the efflux rate was increased. 2′3‐dimercapto‐propanol (BAL) increased the rate of K42 loss from the fibers. It is suggested that this effect of serum albumin is due to its sequestering action on toxic substances (tentatively identified as heavy metals) normally present in trace amounts in Ringer's solutions.