Is HCO₃⁻ transport in anabaena a Na⁺ symport?

Na⁺ strongly promoted HCO₃⁻ transport in Anabaena variabilis, The effect was highly specific to this cation. Kinetic analysis indicated a progressive decrease in the K_m (HCO₃⁻) of the transport system with increasing Na⁺ concentration. V_max was also affected. We raise the possibility that the transport is a Na⁺-HCO₃⁻ symport; alternatively, that a Na⁺-H+ antiport (or Na⁺-OH⁺ symport) system mediates the efflux of the OH⁻ ions derived from the entering HCO₃⁻ ions, and that this antiport can rate-limit HCO₃⁻ influx.