  We use the double exchange (DE) model via degenerate orbitals and
tight-binding approximation to study the magnetoconductivity of a canted
A-phase of pseudo-cubic manganites. It is argued that the model is applicable
in a broad concentration range for manganites with the tolerance factor, t,
close to one. As for the substitutional disorder, scattering on random
Jahn-Teller distortions of MnO6 octahedra is chosen. We emphasize an intimate
correlation between the carrier concentration and resistivity value of metallic
manganites. Magnetoresistance as a function of magnetization is calculated for
a canted A-phase for both in-plane and out-of-plane current directions. A
contact between two manganite phases is considered and structure of the
transition region near the contact is discussed. Numerical calculations show
charge re-distribution near the contact and a large screening length of the
order of five inter-atomic distances. We employed our results to interpret data
obtained in recent experiments on La0.4Sr0.6MnO3/La0.55Sr0.45MnO3
superlattices. We also briefly discuss the relative importance of the
cooperative Jahn-Teller distortions, double exchange mechanism and
super-exchange interactions for the formation of the A-phase at increasing Sr
concentrations x>0.45 in LSMO to suggest that the Jahn-Teller contraction of
octahedra, c/a<1, plays a prevailing role.
