  The isospin-dependent component of the effective nucleon-nucleon interaction
that causes the $\Delta T=1$ (p, p') and (p, n) reactions off nuclei is
studied. It is shown that the corrections to the impulse approximation comes
from the $g$-matrix type correction and the rearrangement term. They are
numerically estimated with the isospin-asymmetric nuclear-matter reaction
matrix approach. The analysis of the isobaric analog transitions
${}^{42}$Ca(p,n)${}^{42}$Sc and ${}^{48}$Ca(p,n)${}^{48}$Sc are presented.
