title: Effects of exogenous hydrogen sulphide on calcium signalling, background (TASK) K channel activity and mitochondrial function in chemoreceptor cells.
abstract: It has been proposed that endogenous H(2)S mediates oxygen sensing in chemoreceptors; this study investigates the mechanisms by which H(2)S excites carotid body type 1 cells. H(2)S caused a rapid reversible increase in intracellular calcium with EC(50) ≈ 6 μM. This [Ca(2+)](i) response was abolished in Ca-free Tyrode. In perforated patch current clamp recordings, H(2)S depolarised type 1 cells from -59 to -35 mV; this was accompanied by a robust increase in [Ca(2+)](i). Voltage clamping at the resting membrane potential abolished the H(2)S-induced rise in [Ca(2+)](i). H(2)S inhibited background K(+) current in whole cell perforated patch and reduced background K(+) channel activity in cell-attached patch recordings. It is concluded that H(2)S excites type 1 cells through the inhibition of background (TASK) potassium channels leading to membrane depolarisation and voltage-gated Ca(2+) entry. These effects mimic those of hypoxia. H(2)S also inhibited mitochondrial function over a similar concentration range as assessed by NADH autofluorescence and measurement of intracellular magnesium (an index of decline in MgATP). Cyanide inhibited background K channels to a similar extent to H(2)S and prevented H(2)S exerting any further influence over channel activity. These data indicate that the effects of H(2)S on background K channels are a consequence of inhibition of oxidative phosphorylation. Whilst this does not preclude a role for endogenous H(2)S in oxygen sensing via the inhibition of cytochrome oxidase, the levels of H(2)S required raise questions as to the viability of such a mechanism.
authors.affiliation: Department of Physiology Anatomy & Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK. keith.buckler@dpag.ox.ac.uk
authors.forename: Keith J
authors.initials: KJ
authors.lastname: Buckler
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D002344:Carotid Body / Q000187:drug effects / Q000378:metabolism; D002628:Chemoreceptor Cells / Q000187:drug effects* / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism; D006862:Hydrogen Sulfide / Q000494:pharmacology*; D000860:Hypoxia / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009419:Nerve Tissue Proteins; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010100:Oxygen / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D024683:Potassium Channels, Tandem Pore Domain / Q000378:metabolism*; D051381:Rats
chemical_list: D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D024683:Potassium Channels, Tandem Pore Domain; D009243:NAD; C420132:potassium channel subfamily K member 3; D003576:Electron Transport Complex IV; D008274:Magnesium; D011188:Potassium; D010100:Oxygen; D002118:Calcium; D006862:Hydrogen Sulfide