Awareness of H 2 S as an important, widespread signalling molecule is growing rapidly. It is known to influence, for example, proliferation of vascular smooth muscle cells and pain sensation [1] . Interestingly, both of these processes involve T-type Ca 2+ channel activity [2] , [3] , and ion channels are emerging as an important family of target proteins for modulation by H 2 S [4] . We have therefore investigated whether H 2 S modulates T-type Ca 2+ channels, using whole-cell patch clamp recordings from HEK293 cells over-expressing, separately, the three known type of T-type Ca 2+ channels, Cav3.1, Cav3.2 and Cav3.3 [5] . Cells were exposed to H 2 S by bath application of NaHS. This agent caused a concentration-dependent (10 μM to 1 mM) inhibition of currents in Cav3.2-expressing cells. Inhibition was observed at all activating test potentials applied, and all subsequent values detailed are taken from currents recorded at a test potential of −20 mV (holding potential −80 mV). Maximal inhibition of 35.3 ± 2.2%, n = 6, P t -test was observed at the NaHS concentration of 1 mM. By contrast, current carried by Cav3.1 channels were unaffected over the same concentration range, and those carried by Cav3.3 were only modestly inhibited (13.2 ± 3.6%, n = 5, P = 0.022) by 1 mM NaHS. Thus, H 2 S appeared to inhibit Cav3.2 channels selectively. Cav3.2 inhibition was only poorly reversible, but current amplitudes could be recovered by dithiothreitol (2 mM; n = 7), suggesting H 2 S acts via channel redox modulation. Given the high selectivity of H 2 S for Cav3.2, we examined its effects in H191Q mutant Cav3.2-expressing cells, since this extracellular histidine residue is known to be essential for redox-sensitive binding of divalent metals [3] . These mutant channels were insensitive to H 2 S (1 mM NaHS, n = 6). In agreement with previous studies (e.g. [6] ), the zinc chelator TPEN (10 μM) augmented Cav3.2 currents, by 150 ± 9.0% (n = 6), and in its presence NaHS was without significant effect on currents carried by Cav3.2 channels. Our data indicate that H 2 S selectively inhibits Cav3.2 T-type Ca 2+ channels heterologously expressed in HEK293 cells. Inhibition requires the extracellular histidine residue H191. Our results do not, however, support the previous suggestion that H 2 S might augment T-type Ca 2+ channel activity by acting as a zinc chelator (reviewed in [3] ).