Mapping of dihydropyridine binding residues in a less sensitive invertebrate L-type calcium channel (LCav1)

Abstract

Invertebrate L-type calcium channel, LCav1, isolated from the pond snail Lymnaea stagnalis is nearly indistinguishable from mammalian Cav1.2 (α1C) calcium channel in biophysical characteristics observed in vitro. These L-type channels are likely constrained within a narrow range of biophysical parameters to perform similar functions in the snail and mammalian cardiovascular systems. What distinguishes snail and mammalian L-type channels is a difference in dihydropyridine sensitivity: 100 nM isradipine exhibits a significant block of mammalian Cav1.2 currents without effect on snail LCav1 currents. The native snail channel serves as a valuable surrogate for validating key residue differences identified from previous experimental and molecular modeling work. As predicted, three residue changes in LCav1 (N_3o18, F_3i10, and I_4i12) replaced with DHP-sensing residues in respective positions of Cav1.2, (Q_3o18, Y_3i10, and M_4i12) raises the potency of isradipine block of LCaV1 channels to that of mammalian Cav1.2. Interestingly, the single N_3o18_Q mutation in LCav1 channels lowers DHP sensitivity even further and the triple mutation bearing enhanced isradipine sensitivity, still retains a reduced potency of agonist, (S)-Bay K8644.