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Background [K.sup.+] channels of the TASK family are believed to participate in sensory transduction by chemoreceptor (glomus) cells of the carotid body (CB). However, studies on the systemic CB-mediated ventilatory response to hypoxia and hypercapnia in TASK1- and/or TASK3-deficient mice have yielded conflicting results. We have characterized the glomus cell phenotype of TASK-null mice and studied the responses of individual cells to hypoxia and other chemical stimuli. CB morphology and glomus cell size were normal in wild-type as well as in [TASK1.sup.-/-] or double [TASK1/3.sup.-/-] mice. Patch-clamped TASK1/3-null glomus cells had significantly higher membrane resistance and less hyperpolarized resting potential than their wild-type counterpart. These electrical parameters were practically normal in [TASK1.sup.-/-] cells. Sensitivity of background currents to changes of extracellular pH was drastically diminished in TASK1/3-null cells. In contrast with these observations, responsiveness to hypoxia or hypercapnia of either [TASK1.sup.-/-] or double [TASK1/3.sup.-/-] cells, as estimated by the amperometric measurement of catecholamine release, was apparently normal. TASK1/3 knockout cells showed an enhanced secretory rate in basal (normoxic) conditions compatible with their increased excitability. Responsiveness to hypoxia of TASK1/3-null cells was maintained after pharmacological blockade of maxi-[K.sup.+] channels. These data in the TASK-null mouse model indicate that TASK3 channels contribute to the background [K.sup.+] current in glomus cells and to their sensitivity to external pH. They also suggest that, although TASK1 channels might be dispensable for [O.sub.2]/C[O.sub.2] sensing in mouse CB cells, TASK3 channels (or TASK1/3 heteromers) could mediate hypoxic depolarization of normal glomus cells. The ability of [TASK1/3.sup.-/-] glomus cells to maintain a powerful response to hypoxia even after blockade of maxi-[K.sup.+] channels, suggests the existence of multiple sensor and/or effector mechanisms, which could confer upon the cells a high adaptability to maintain their chemosensory function. doi/10.1085/jgp.200910302

The virulence of the opportunistic pathogen Pseudomonas aeruginosa involves the coordinate expression of many virulence factors, including type IV pill, which are required for colonization of host tissues and for twitching motility. Type IV pilus function is controlled in part by the Chp chemosensory system, which includes a histidine kinase, ChpA, and two CheY-like response regulators, PilG and PilH. How the Chp components interface with the type IV pilus motor proteins PilB, PilT, and PilU is unknown. We present genetic evidence confirming the role of ChpA, PilG, and PilB in the regulation of pilus extension and the role of PilH and PilT in regulating pilus retraction. Using informative double and triple mutants, we show that (i) ChpA, PilG, and PilB function upstream of PilH, PilT, and PilU; (ii) that PilH enhances PilT function; and (iii) that PilT and PilB retain some activity in the absence of signaling input from components of the Chp system. By site-directed mutagenesis, we demonstrate that the histidine kinase domain of ChpA and the phosphoacceptor sites of both PilG and PilH are required for type IV pilus function, suggesting that they form a phosphorelay system important in the regulation of pilus extension and retraction. Finally, we present evidence suggesting that pilA transcription is regulated by intracellular PilA levels. We show that PilA is a negative regulator of pill transcription in P. aeruginosa and that the Chp system functionally regulates pilA transcription by controlling PilA import and export. doi:10.1128/JB.01390-09

Hypoxia activates chemoreceptor cells of the carotid body (CB) promoting an increase in their normoxic release of neurotransmitters. Catecholamine (CA) release rate parallels the intensity of hypoxia. Coupling of hypoxia to CA release requires cell depolarization, produced by inhibition of [O.sub.2]-regulated [K.sup.+] channels, and [Ca.sup.2+] entering the cells via voltage-operated channels. In rat chemoreceptor cells hypoxia inhibits large-conductance, calcium-sensitive K channels (maxiK) and a two-pore domain weakly inward rectifying [K.sup.+] channel (TWIK)-like acid-sensitive [K.sup.+] channel (TASK)-like channel, but the significance of maxiK is controversial. A proposal envisions maxiK contributing to set the membrane potential ([E.sub.m]) and the hypoxic response, but the proposal is denied by authors finding that maxiK inhibition does not depolarize chemoreceptor cells or alters intracellular [Ca.sup.2+] concentration or CA release in normoxia or hypoxia. We found that maxiK channel blockers (tetraethylammonium and iberiotoxin) did not modify CA release in rat chemoreceptor cells, in either normoxia or hypoxia, and iberiotoxin did not alter the [Ca.sup.2+] transients elicited by hypoxia. On the contrary, both maxiK blockers increased the responses elicited by dinitrophenol, a stimulus we demonstrate does not affect maxiK channels in isolated patches of rat chemoreceptor cells. We conclude that in rat chemoreceptor cells maxiK channels do not contribute to the genesis of the [E.sub.m], and that their full inhibition by hypoxia, preclude further inhibition by maxiK channel blockers. We suggest that full inhibition of this channel is required to generate the spiking behavior of the cells in acute hypoxia. hypoxia; catecholamine; iberiotoxin; intracellular calcium

The Aer and Tsr chemoreceptors in Escherichia coli govern tactic responses to oxygen and redox potential that are parts of an overall behaviour known as energy taxis. They are also proposed to mediate responses to rapidly utilized carbon sources, glycerol and succinate, via the energy taxis mechanism. In this study, the Aer and Tsr proteins were individually expressed in an 'all-transducer-knockout' strain of E. coli and taxis was analysed in gradients of various oxidizable carbon sources. In addition to the known response to glycerol and succinate, it was found that Aer directed taxis towards ribose, galactose, maltose, malate, proline and alanine as well as the phosphotransferase system (PTS) carbohydrates glucose, mannitol, mannose, sorbitol and fructose, but not to aspartate, glutamate, glycine and arabinose. Tsr directed taxis towards sugars (including those transported by the PTS), but not to organic acids or amino acids. When a mutated Aer protein unable to bind the FAD cofactor was expressed in the receptor-less strain, chemotaxis was not restored to any substrate. Aer appears to mediate responses to rapidly oxidizable substrates, whether or not they are effective growth substrates, whereas Tsr appears to mediate taxis to substrates that support maximal growth, whether or not they are rapidly oxidizable. This correlates with the hypothesis that Aer and Tsr sense redox and proton motive force, respectively. Taken together, the results demonstrate that Aer and Tsr mediate responses to a broad range of chemicals and their attractant repertoires overlap with those of specialized chemoreceptors, namely Trg (ribose, galactose) and Tar (maltose).

Olfactory receptor (OR) genes constitute the basis for the sense of smell and are encoded by the largest mammalian gene superfamily of >1,000 genes. In humans, >60% of these are pseudogenes. In contrast, the mouse OR repertoire, although of roughly equal size, contains only [approximately equal to] 20% pseudogenes. We asked whether the high fraction of nonfunctional OR genes is specific to humans or is a common feature of all primates. To this end, we have compared the sequences of 50 human OR coding regions, regardless of their functional annotations, to those of their putative orthologs in chimpanzees, gorillas, orangutans, and rhesus macaques. We found that humans have accumulated mutations that disrupt OR coding regions roughly 4-fold faster than any other species sampled. As a consequence, the fraction of OR pseudogenes in humans is almost twice as high as in the non-human primates, suggesting a human-specific process of OR gene disruption, likely due to a reduced chemosensory dependence relative to apes.

Research has been conducted on inflammatory cells. The influx of these cells to injury sites has been investigated in studying the cell ability to form chemotactic gradients, and the details are reported.

Research has been conducted on the receptor methylation in Escherichia coli chemotaxis. The role of this receptor in adaptation has been investigated and the details are reported.

Research has been conducted on CheZ phosphatase. The authors report that they have investigated the conditions required for CheZ phosphatase polar localization via the use of CheZ green fluorescent fusion protein, and that CheZ localization requires the truncated C-terminal portion of P1 domain in CheA-short.