CFTR: transport HCO3- ions?

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I would like to know if the Cystic Fibrosis Trans-membrane Regulator protein is also involved in HCO3- ion transport in addition to Cl- ion transport?

I was doing an A level question - and the data in the question seemed to suggest that HCO3- ion transport decreased upon a mutation in the CFTR.
But i was confused as i thought the mutation affects Cl- ion transport.

Any theories?

If you want, I can post the question here too.