  We investigate the equation of state of asymmetric nuclear matter and its
isospin dependence in various spin-isospin $ST$ channels within the framework
of the Brueckner-Hartree-Fock approach extended to include a microscopic
three-body force (TBF). It is shown that the potential energy per nucleon in
the isospin-singlet T=0 channel is mainly determined by the contribution from
the tensor SD coupled channel. At high densities, the TBF effect on the
isospin-triplet T=1 channel contribution turns out to be much larger than that
on the T=0 channel contribution. At low densities around and below the normal
nuclear matter density, the isospin dependence is found to come essentially
from the isospin-singlet SD channel and the isospin-triplet T=1 component is
almost independent of isospin-asymmetry. As the density increases, the T=1
channel contribution becomes sensitive to the isospin-asymmetry and at high
enough densities its isospin-dependence may even become more pronounced than
that of the T=0 contribution. The present results may provide some microscopic
constraints for improving effective nucleon-nucleon interactions in nuclear
medium and for constructing new functionals of effective nucleon-nucleon
interaction based on microscopic many-body theories.
