how does blocking the potassium channel affect calcium release?

The K channels are used to return the ion concentration to normal. The influx of K+ into the neurone leads to repolarisation, so the membrane potential returns to normal. Blocking the K channels could possibly prolong the period of depolarisation. During depolarisation, the permeability of the presynaptic membrane to Ca2+ ions increases, stimulating the release of neurotransmitters into the synaptic cleft.  If the K channels are blocked, this would mean more Ca2+ is released, leading to excessive release of neurotransmitter.

Hope this helps a little. (: