Enables the transfer of lactate from one side of a membrane to the other. Lactate is 2-hydroxypropanoate, CH3-CHOH-COOH; L(+)-lactate is formed by anaerobic glycolysis in animal tissues, and DL-lactate is found in sour milk, molasses and certain fruit juices.
monocarboxylate (lactate, pyruvate, mevalonate) uptake/efflux porter activity