Hydrogen Sulfide Inhibits Human BKCa Channels

Abstract

Hydrogen sulfide (H(2)S) is produced endogenously in many types of mammalian cells. Evidence is now accumulating to suggest that H(2)S is an endogenous signalling molecule, with a variety of molecular targets, including ion channels. Here, we describe the effects of H(2)S on the large conductance, calcium-sensitive potassium channel (BK(Ca)). This channel contributes to carotid body glomus cell excitability and oxygen-sensitivity. The experiments were performed on HEK 293 cells, stably expressing the human BK(Ca) channel alpha subunit, using patch-clamp in the inside-out configuration. The H(2)S donor, NaSH (100microM-10 mM), inhibited BK(Ca) channels in a concentration-dependent manner with an IC(50) of ca. 670microM. In contrast to the known effects of CO donors, the H(2)S donor maximally decreased the open state probability by over 50% and shifted the half activation voltage by more than +16mV. In addition, although 1 mM KCN completely suppressed CO-evoked channel activation, it was without effect on the H(2)S-induced channel inhibition, suggesting that the effects of CO and H(2)S were non-competitive. RT-PCR showed that mRNA for both of the H(2)S-producing enzymes, cystathionine-beta-synthase and cystathionine-gamma-lyase, were expressed in HEK 293 cells and in rat carotid body. Furthermore, immunohistochemistry was able to localise cystathionine-gamma-lyase to glomus cells, indicating that the carotid body has the endogenous capacity to produce H(2)S. In conclusion, we have shown that H(2)S and CO have opposing effects on BK(Ca)channels, suggesting that these gases have separate modes of action and that they modulate carotid body activity by binding at different motifs in the BK(Ca)alphasubunit.

Hydrogen sulfide (H2S) and hypoxia inhibit salmonid gastrointestinal motility: evidence for H2S as an oxygen sensor

“…P O2 , (4) inhibitors of H 2 S synthesis inhibit hypoxic responses, and (5) potential sulfide donors augment the hypoxic responses. Recent studies on the mammalian carotid body Peng et al, 2010;Telezhkin et al, 2009;Telezhkin et al, 2010) and kidney (Beltowski, 2010) have supported this hypothesis and our assertion that this is a phylogenetically ancient and ubiquitous O 2 -sensing mechanism. The present study extends these observations to the fish GI tract and supports the hypothesis that O 2 -dependent H 2 S metabolism is a fundamental oxygen-sensing mechanism.…”

“…the 'O 2 sensor' . Evidence for this mechanism has been found in systemic and respiratory vascular smooth muscle Olson et al, 2008a;, urinary bladder smooth muscle , chromaffin cells (Perry et al, 2009) and O 2 -sensing chemoreceptor cells Olson et al, 2008b;Peng et al, 2010;Telezhkin et al, 2009;Telezhkin et al, 2010).…”

Hydrogen sulfide as an oxygen sensor

“…2B) (60,139). In the carotid body, it has been proposed that hypoxia inhibits constitutive CO production by hemeoxygenase 2 (HO-2), which then relieves the heretofore tonic inhibitory effect of CO on cystathionine c-lyase (CSE) and H 2 S levels increase, closing largeconductance Ca 2 + -dependent K + channels (BK Ca ) (87,162,163) or TWIK-related acid-sensitive potassium (TASK) (15) channels. This depolarizes glomus cells and releases neurotransmitter.…”

“…5B) (87,162,163) or TASK channels (15). Li et al (87) showed that in whole cell recordings of mouse glomus cells, both hypoxia and H 2 S inhibited BK Ca channels and AOA could inhibit the hypoxic affect.…”

“…Conversely, hypoxic hyperventilation is not affected in HO-2 null mice (131). H 2 S appears to have more of a direct effect on BK Ca channels, whereas CO appears modulatory (162,163) and HO inhibitors such as zinc protoporphyrin IX directly bind to H 2 S (33). Obviously, this field needs an additional study.…”