Ion-specific protein destabilization of the contractile proteins of cardiac muscle fibers

Abstract

 We investigated the inhibitory effects of increased salt concentrations on maximal calcium-activated force (F _max) of rabbit cardiac papillary muscle bundles skinned with Triton X-100. While other studies have reported a lack of ion-specific effects on F _max of cardiac muscle, we clearly demonstrated the presence of such effects when a wider variety of salts was investigated. In addition, like skeletal muscle, cardiac muscle was found to be sensitive to ionic strength and not to ionic equivalence. In support of our hypothesis that the ion-specific effects are due to protein destabilization, we found that a protein stabilizer (trimethylamine N-oxide, TMAO) completely abolished the ion-specific effects on F _max. The ion-specific effect is probably due to binding of ions to the contractile proteins. The general ionic effect is most likely due to electrostatic shielding that remains in the presence of TMAO. Neither 300 mM sucrose nor TMAO significantly altered F _max at physiological ionic strength indicating that the ion-specific depression of F _max was not due to a colligative/osmotic effect. Furthermore, adding sucrose to solutions with a supraphysiological ionic strength caused a further decrease in F _max indicating that certain osmolytes can alter F _max if the contractile proteins are initially destabilized.