Hypocalcemia causes a decrease in threshold potential, explaining why you get all those hyperexcitability signs with a low serum Ca2+. Hypercalcemia does the opposite. My understanding was that the threshold potential is the point where Na+ conductance (and influx) just exceed K+ conductance (and efflux). Based on this, these serum calcium levels must be having some sort of effect on the sodium or potassium channels. I looked through a bunch of texts and online and couldn't find any explanation as for how changes in serum calcium alter the threshold potential. Is this just because nobody has any idea?