U.S. stocks ended mixed in a volatile session Wednesday. The Dow Jones industrial average rose 53.62, or 0.2 percent, to 33,730.89. The broader Standard & Poor's 500 index fell 16.93, or 0.4 percent, to 4,124.66. The technology-heavy Nasdaq composite index fell 138.26, or 1 percent, to 13,857.84.