  We present an estimate of the bolometric X-ray luminosity - velocity
dispersion L_x - sigma_v relation measured from a new, large and homogeneous
sample of 171 low redshift, X-ray selected galaxy clusters. The linear fitting
of log(L_x) - log(sigma_v) gives L_x = 10^{32.72 \pm 0.08} sigma^{4.1 \pm
0.3}_v erg s^{-1} h^{-2}_{50}. Furthermore, a study of 54 clusters, for which
the X-ray temperature of the intracluster medium T is available, allows us to
explore two other scaling relations, L_x -T and sigma_v -T. From this sample we
obtain L_x \propto T^{3.1 \pm 0.2} and sigma_v \propto T^{1.00 \pm 0.16}, which
are fully consistent with the above result for the L_x-sigma_v. The slopes of
L_x -T and sigma_v -T are incompatible with the values predicted by
self-similarity (L_x \propto T^{2} \propto \sigma_v^4), thus suggesting the
presence of non-gravitational energy sources heating up the intracluster
medium, in addition to the gravitational collapse, in the early stages of
cluster formation. On the other hand, the result on log(L_x) - log(sigma_v)
supports the self-similar model.
