A,B,C, ProTx I Dose response (left), steady state inactivation (middle) and current voltage relations (right) for hCav3.1, hCav3.2 and hCav3.3, respectively. Steady state inactivation and current voltage relations were recorded prior and after application of 1 μM ProTx I. Ensemble dose response curves for tonic channel inhibition by ProTx I were fitted via the Hill equation and IC50’s for hCav3.1, 3.2 and 3.3 were 0.64, 94.6 and 5.4 μM respectively. Insets are representative current traces of each calcium channel before and after (red trace) application of 1 μM ProTx I (Note that the trace for hCav3.1 is the same as in figure 1). All other data were fitted with the Boltzmann equation and are from multiple paired experiments [n = 5-6 per channel]. Note the negative shift in both the half activation and steady state inactivation potential in the presence of 1 μM ProTx I for hCav3.2 despite this concentration having minimal effect on tonic block.