Catalysis of the transfer of a solute or solutes from one side of a membrane to the other according to the reaction: (R)-carnitine(out) + 4-(trimethylammonio)butanoate(in) = (R)-carnitine(in) + 4-(trimethylammonio)butanoate(out).
Catalysis of the transfer of a solute or solutes from one side of a membrane to the other according to the reaction: (R)-carnitine(out) + 4-(trimethylammonio)butanoate(in) = (R)-carnitine(in) + 4-(trimethylammonio)butanoate(out). (en)