P64 Hydrogen sulfide inhibits Cav 3.2 T-type Ca2+ channels

H 2 S is emerging as an important regulator of ion channels [1] , effects which may account for many of this gasotransmitter’s biological actions. Here, we have explored its ability to modulate T-type Ca 2+ channels. H 2 S (applied as NaHS) caused a concentration-dependent inhibition of currents recorded in Cav3.2-expressing HEK293 cells using the whole-cell patch-clamp technique. Inhibition was voltage-independent and maximal inhibition ( ca. 35%) was observed at 1 mM NaHS. In contrast, Cav3.1 channel activity was unaffected, and Cav3.3 channel activity only modestly inhibited ( ca. 13%), over this concentration range. The redox-sensitive extracellular residue H191 [2] was essential for H 2 S sensitivity: currents evoked in mutant Cav3.2 (H191Q)-expressing cells were insensitive to NaHS, and the analogous reverse mutation in Cav3.1 (Q172H [3] ) conferred sensitivity to NaHS on Cav3.1. As previously reported [4] , the zinc chelator TPEN (10 μM) augmented Cav3.2 activity, but augmented currents were also inhibited by NaHS, suggesting H 2 S inhibition occurred independently of zinc binding by this channel. We also explored the ability of H 2 S to inhibit native T-type currents: in rat aortic smooth muscle (A7r5) cells currents were modestly ( ca. 20% were observed. We are currently exploring whether differential effects are attributable to differential channel isoform expression. Our data clearly indicate that H 2 S selectively inhibits Cav3.2 T-type Ca 2+ channels and requires the presence of H191.