  If the second Betti number b_2 of a Sasaki-Einstein manifold Y^7 does not
vanish, then M-theory on AdS_4 x Y^7 possesses "topological" U(1)^{b_2} gauge
symmetry. The corresponding Abelian gauge fields come from three-form
fluctuations with one index in AdS_4 and the other two in Y^7. We find black
membrane solutions carrying one of these U(1) charges. In the zero temperature
limit, our solutions interpolate between AdS_4 x Y^7 in the UV and AdS_2 x R^2
x squashed Y^7 in the IR. In fact, the AdS_2 x R^2 x squashed Y^7 background is
by itself a solution of the supergravity equations of motion. These solutions
do not appear to preserve any supersymmetry. We search for their possible
instabilities and do not find any. We also discuss the meaning of our charged
membrane backgrounds in a dual quiver Chern-Simons gauge theory with a global
U(1) charge density. Finally, we present a simple analytic solution which has
the same IR but different UV behavior. We reduce this solution to type IIA
string theory, and perform T-duality to type IIB. The type IIB metric turns out
to be a product of the squashed Y^7 and the extremal BTZ black hole. We discuss
an interpretation of this type IIB background in terms of the (1+1)-dimensional
CFT on D3-branes partially wrapped over the squashed Y^7.
