  We investigate the neutron and proton single particle (s.p.) potentials of
asymmetric nuclear matter and their isospin dependence in various spin-isospin
$ST$ channels within the framework of the Brueckner-Hartree-Fock approach. It
is shown that in symmetric nuclear matter, the s.p. potentials in both the
isospin-singlet T=0 channel and isospin-triplet T=1 channel are essentially
attractive, and the magnitudes in the two different channels are roughly the
same. In neutron-rich nuclear matter, the isospin-splitting of the proton and
neutron s.p. potentials turns out to be mainly determined by the
isospin-singlet T=0 channel contribution which becomes more attractive for
proton and more repulsive for neutron at higher asymmetries.
