functional defects in the L type calcium channel.
low extracellular calcium
increased space between the L type channel and ryanodine receptor
abnormalities in the ryanodine receptor
there are three mechanisms to lead to a decrease in SR calcium content:
1. One was reduced uptake in the calcium and to the SR
2. if we have more extrusion from the cell, and leaving less calcium that can be taken up into the SR
3. ryanodine receptors that are not fully closed in diastole so they actually are leaking calcium in diastole and therefore, there's less calcium in the SR that can be released when it's really needed.