Okays, thanks.
However it does not exactly meet my needs:

Not all pins will be triggered when they go from High to Low.

My program gets an IR signal on a sensor connected to a PORTA pin and this triggers an INT. In the int routine, I check what pin received the IR signal and then I poll the pin to get a signal that is encoded.
On pin RA5, I set no WPU because the default state will be 0V and once 5V gets to this pin, it triggers an INT.

(I'm developping software and hardware for a lasergame).

Anyway thank you very much for your help.