Hi, no transistors, the arduino has a set of registers which enable or disable each pin for generating pin change interrupts. If you disable the interrupt at this level you can leave interrupts attached and disable specific pins until you need them. You can then enable/disable as often as you want with no overhead when they are not in use and no memory leaks from attach/detach
Im in Ethiopia today so no time to dig out the register names.
Duane B