You do not mention the conductance of your channel. The problems with most
'animal' calcium channels are that they are of too small conductance to be
reliably recorded at physiological calcium ion concentrations. Some
improvement is seen when barium is used as the permeant ion but even then
the largest single channel conductance, with 90 mM Ba, is about 25 pS.
Furthermore, these channels are prone to very short, flickery openings so
that a clear open channel conductance is often difficult to obtain. The
best shot for doing a concentration/conductance relation is to examine the
L-type channel in the presence of BayK (a dihydropyridine inhibitor of
deactivation) but even then the conductance window is small.
What are the characteristics of your channel - conductance, open channel