Re: 1. What is the calcuim ion concentration in the standard muscle cell

The extracellular Calcium concentration for mammalian skeletal muscle is 
1.5 mM, the intracellular concentration is 10-7 M.  For your experiments, 
you will probably only be able to change the extracellular calcium 
concentation, so I would use concentrations ranging 100 fold in either 
direction of 1.5 mM.

Ref: Hille, B., Ion channels of excitable membranes, 1992, 2nd ed., 
Sinauer Associates, Inc, page 15.