  The nature of the out-of-plane dissipation was investigated in underdoped
$Y_{0.54}Pr_{0.46}Ba_{2}Cu_{3}O_{7-\delta}$ single crystals at temperatures
close to the critical temperature. For this goal, temperature and angle
dependent out-of-plane resistivity measurements were carried out both below and
above the critical temperature. We found that the Ambegaokar-Halperin
relationship [V. Ambegaokar, and B. I. Halperin, Phys. Rev. Lett. \textbf{22},
1364 (1969)] depicts very well the angular magnetoresistivity in the
investigated range of field and temperature. The main finding is that the
in-plane phase fluctuations decouple the layers above the critical temperature
and the charge transport is governed only by the quasiparticles. We also have
calculated the interlayer Josephson critical current density, which was found
to be much smaller than the one predicted by the theory of layered
superconductors. This discrepancy could be a result of the d-wave symmetry of
the order parameter and/or of the non BCS temperature dependence of the c-axis
penetration length.
