Is HCO(3) Transport in Anabaena a Na Symport?

Na(+) strongly promoted HCO(3) (-) transport in Anabaena variabilis. The effect was highly specific to this cation. Kinetic analysis indicated a progressive decrease in the K(m) (HCO(3) (-)) of the transport system with increasing Na(+) concentration. V(max) was also affected. We raise the possibility that the transport is a Na(+)-HCO(3) (-) symport; alternatively, that a Na(+)-H(+) antiport (or Na(+)-OH(+) symport) system mediates the efflux of the OH(-) ions derived from the entering HCO(3) (-) ions, and that this antiport can rate-limit HCO(3) (-) influx.