How can I rid a mattress of cat urine smell?

You sure are having a lot of trouble with mattresses...

http://able2know.org/user/michaelbevan/

When this happened to me I simply got Bingo, the dog, to piss all over the bed. I then rolled around in the middle where most of the previous drenching had occurred to mix the aromas together as much as possible.

Bingo accommodated me on several occasions until I was sure I couldn't smell cat urine any more. Lucky, the cat, has never been near the bed since thank goodness, although it did take quite some weeks to dry completely and I spent some sleepless nights tossing and turning what with the nightmares and the residual dankness.

Unfortunately, Bingo has had to be kept outside from that time on for one reason or another.

I drew quite some solace from the realisation that for this problem there was a solution.

If you've already had it professionally cleaned and that didn't work, then I think that's the most you can do. You'll probably have to get a new mattress...