Transporter that facilitates the transmembrane diffusion of water, dihydroxyacetone, glycerol, urea, H(2)O(2) and D/L-lactic acid. Is involved in the cellular racemization of lactate and lactate metabolism, but has likely a more general physiological role. The transported molecule is indeed lactic acid and not the lactate anion, in agreement with the assumption that, with very few exceptions, MIPs (major intrinsic proteins) only facilitate the transport of uncharged solutes. Cells lacking this gene show a decreased lactate transport ability. Belongs to the MIP/aquaporin (TC 1.A.8) family.