RESUMO
Blood plasma, serum and its fractions containing components of different molecular weights as well as some identified serum constituents were tested for their action on sodium currents of voltage-clamped, internally dialyzed neuroblastoma cells. Only components with a molecular weight over 50 kDa produced a persistent increase in sodium channel currents (stimulatory effect) and shifts in activation and inactivation curves along the voltage axis towards more negative or positive potentials, respectively (modifying effect). Both modulations taken together provide a somewhat higher level of sodium electro-excitable system activity. Among the identified serum components tested, including those possessing high physiological activity, albumin was the only one which reproduced the effects of whole blood serum both qualitatively and quantitatively. The data obtained allow to assume albumin to play a role of an active substance responsible for the blood plasma or serum effects on the potential-dependent transporting system in the neuroblastoma cell membrane. Albumin seems to be involved in holding the functional activity of sodium channels on a suitable level rather than being involved in any regulatory processes.
