Ion-channel blocker sensitivity of voltage-gated calcium-channel homologue Cch1 in Saccharomyces cerevisiae

The Cch1 protein of the yeast Saccharomyces cerevisiae is a homologue of the pore-forming x(1) subunit of mammalian voltage-gated Ca2+, channels (VGCCs), and it constitutes a high-affinity Ca2+-influx system with the Mid1 protein in this organism. Here, we characterized the kinetic property of a putative Cch1-Mid1 Ca2+ channel overexpressed in S. cerevisiae cells, and showed that the L-type VGCC blockers nifedipine and verapamil partially inhibited Cch1-Mid1 activity, but typical P/Q-, N-, R- and T-type VGCC blockers did not inhibit activity. In contrast, a third L-type VGCC blocker, diltiazem, increased Cch1-Mid1 activity. Diltiazem did not increase Ca2+ uptake in the cch1 Delta and mid1 Delta single mutants and the cch1 Delta mid1 Delta double mutant, indicating that the diltiazem-induced increase in Ca2+ uptake is completely dependent on Cch1-Mid1. These results suggest that Cch1 is pharmacologically similar to L-type VGCCs, but the interactions between Cch1 and the L-type VGCC blockers are more complicated than expected.