A method is presented to describe quantitatively the influences of electrostatic interactions on local conformational changes and to demonstrate their effect on the static chain flexibility. This was done within the rotational isomeric state scheme (RIS) by incorporating Coulomb interaction energies and introducing electrostatic statistical weights in the matrices of the conformational partition function. As a main result we found constant flexibilities for a wide range of counterion concentrations. The screening effect of counterions surrounding the individual charge carriers on the chain backbone starts only at concentrations where intercharge distances and the screening length of the ionic atmospheres are of the same order of magnitude. Electrostatic interactions between polyion charges are mainly determined by bare Coulomb forces.