glutamate/gaba balance and calcium

Could you explain what affects glutamate and gaba balance and how they compete or balance? I.e. what could cause glutamate to be high, and would than in turn cause gaba to be low?

Also - what role does calcium play with glutamate, I heard the 2 were a bad combination, and some use an anolgy that glutamate is a gun and calciuma bullet, but what damage would it be causing? Tweet