The values of the Young's modulus of bilayer membranes (BLM) in transverse direction E perpendicular low compared to the same E parallel in BLM plane, may be determined by the capacity method only for membranes with alternative thickness. The measured values of thickness change characterize in general the striction of thin regions of the BLM. In the case of large transverse dimensions of microinhomogeneities the BLM reflectivity change is a function of the dilation of thick BLM regions but not striction of its thin regions induced with electrical potential.