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Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) channel, an ATP binding cassette (ABC) transporter. CFTR gating is linked to ATP binding and dimerization of its two nucleotide binding domains (NBDs). Channel activation also requires phosphorylation of the R domain by poorly understood mechanisms. Unlike conventional ligand-gated channels, CFTR is an ATPase for which ligand (ATP) release typically involves nucleotide hydrolysis. The extent to which CFTR gating conforms to classic allosteric schemes of ligand activation is unclear. Here, we describe point mutations in the CFTR cytosolic loops that markedly increase ATP-independent (constitutive) channel activity. This finding is consistent with an allosteric gating mechanism in which ligand shifts the equilibrium between inactive and active states but is not essential for channel opening. Constitutive mutations mapped to the putative symmetry axis of CFTR based on the crystal structures of related ABC transporters, a common theme for activating mutations in ligand-gated channels. Furthermore, the ATP sensitivity of channel activation was strongly enhanced by these constitutive mutations, as predicted for an allosteric mechanism (reciprocity between protein activation and ligand occupancy). Introducing constitutive mutations into CFTR channels that cannot open in response to ATP (i.e., the G551D CF mutant and an NBD2-deletion mutant) substantially rescued their activities. Importantly, constitutive mutants that opened without ATP or NBD2 still required R domain phosphorylation for optimal activity. Our results confirm that (i) CFTR gating exhibits features of protein allostery that are shared with conventional ligandgated channels and (ii) the R domain modulates CFTR activity independent of ATP-induced NBD dimerization.ATP binding cassette transporter | cystic fibrosis | ligand | constitutive | mutant C ystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP binding cassette (ABC) transporter superfamily, although it is the only known ion channel in this transporter family (1). Like other ABC transporters, CFTR uses ATP binding to its two nucleotide binding domains (NBDs) to drive conformational rearrangements of its transmembrane domains (2, 3). CFTR channel opening is linked to ATP binding to each of two sites at the interface of an NBD1-NBD2 dimer (2, 3). Subsequent hydrolysis, typically at site 2 (primarily composed of sequences from NBD2), promotes channel closure by clearing ligand from this site (4, 5). The coupling between ATP binding and pore opening is presumably mediated by the cytosolic loops that physically link the NBDs to the transmembrane domains (6, 7).Because CFTR is an enzyme that normally hydrolyzes its ligand as part of the channel gating cycle, the extent to which its properties are similar to those of more conventional ligand-gated channels is an interesting issue. Ligand-gated channels such as acetylcholine receptors obey the principles of protein alloster...

ATP-sensitive K؉ (K ATP ) channels may be regulated by protons in addition to ATP, phospholipids, and other nucleotides. Such regulation allows a control of cellular excitability in conditions when pH is low but ATP concentration is normal. However, whether the K ATP changes its activity with pH alterations remains uncertain. In this study we showed that the reconstituted K ATP was strongly activated during hypercapnia and intracellular acidosis using whole-cell recordings. Further characterizations in excised patches indicated that channel activity increased with a moderate drop in intracellular pH and decreased with strong acidification. The channel activation was produced by a direct action of protons on the Kir6 subunit and relied on a histidine residue that is conserved in all K ATP . The inhibition appeared to be a result of channel rundown and was not seen in whole-cell recordings. The biphasic response may explain the contradictory pH sensitivity observed in cell-endogenous K ATP in excised patches. Site-specific mutations of two residues showed that pH and ATP sensitivities were independent of each other. Thus, these results demonstrate that the proton is a potent activator of the K ATP . The pH-dependent activation may enable the K ATP to control vascular tones, insulin secretion, and neuronal excitability in several pathophysiologic conditions. Hypercapnia and acidosis affect vascular tone, skeletal muscle contractility, insulin secretion, epithelial transport, and neuronal excitability, which may be mediated by K ATP 1 (1-5). However, previous studies on the pH sensitivity of these K ϩ channels were controversial and even contradictory. In the absence of ATP, acidic pH was shown to stimulate cell-endogenous K ATP (6, 7), inhibit it (8, 9), and have little or no effect (10, 11). This inconsistency is further complicated by the indirect effect of ATP or Mg 2ϩ and tissue-specific K ATP species (8 -12). Consequently, it is unclear whether K ATP is modulated during hypercapnia and acidosis and what molecular mechanisms are underlying the modulations. The cloned K ATP channels are ideal for addressing these questions because they allow for fine dissection of the modulatory mechanisms and elaborate manipulation of PCO 2 and pH in an expression system (13,14). Therefore, we studied the modulation of the cloned K ATP (Kir6 with SUR, Ref. 15) by CO 2 and acidic pH. To locate the pH sensors, we also studied Kir6.2 with a truncation of 36 amino acids at the C terminus (Kir6.2⌬C36) because it expresses functional channel without the SUR subunit and retains fair ATP sensitivity (16). MATERIALS AND METHODSOocytes from Xenopus laevis were used in the present studies. Frogs were anesthetized by bathing them in 0.3% 3-aminobenzoic acid ethyl ester. A few lobes of ovaries were removed after a small abdominal incision (ϳ5 mm). Then, the surgical incision was closed and the frogs were allowed to recover from the anesthesia. Xenopus oocytes were treated with 2 mg/ml collagenase (Type I, Sigma) in an OR2 solution consistin...

There is growing evidence that ketone bodies, which are derived from fatty acid oxidation and usually produced in fasting state or on high-fat diets have broad neuroprotective effects. Although the mechanisms underlying the neuroprotective effects of ketone bodies have not yet been fully elucidated, studies in recent years provided abundant shreds of evidence that ketone bodies exert neuroprotective effects through possible mechanisms of anti-oxidative stress, maintaining energy supply, modulating the activity of deacetylation and inflammatory responses. Based on the neuroprotective effects, the ketogenic diet has been used in the treatment of several neurological diseases such as refractory epilepsy, Parkinson's disease, Alzheimer's disease, and traumatic brain injury. The ketogenic diet has great potential clinically, which should be further explored in future studies. It is necessary to specify the roles of components in ketone bodies and their therapeutic targets and related pathways to optimize the strategy and efficacy of ketogenic diet therapy in the future.

Sleep is a fundamental homeostatic process, and disorders of sleep can greatly affect quality of life. Parkinson's disease (PD) is highly comorbid for a spectrum of sleep disorders and deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been reported to improve sleep architecture in PD. We studied local field potential (LFP) recordings in PD subjects undergoing STN-DBS over the course of a full-night's sleep. We examined the changes in oscillatory activity recorded from STN between ultradian sleep states to determine whether sleep-stage dependent spectral patterns might reflect underlying dysfunction. For this study, PD (n=10) subjects were assessed with concurrent polysomnography and LFP recordings from the DBS electrodes, for an average of 7.5 hours in 'off' dopaminergic medication state. Across subjects, we found conserved spectral patterns among the canonical frequency bands (delta 0-3 Hz, theta 3-7 Hz, alpha 7-13 Hz, beta 13-30 Hz, gamma 30-90 Hz and high frequency 90-350 Hz) that were associated with specific sleep cycles: delta (0-3 Hz) activity during non-rapid eye movement (NREM) associated stages was greater than during Awake, whereas beta (13-30 Hz) activity during NREM states was lower than Awake and rapid eye movement (REM). In addition, all frequency bands were significantly different between NREM states and REM. However, each individual subject exhibited a unique mosaic of spectral interrelationships between frequency bands. Our work suggests that LFP recordings from human STN differentiate between sleep cycle states, and sleep-state specific spectral mosaics may provide insight into mechanisms underlying sleep pathophysiology.

Abstract-ATP-sensitive K ϩ channels (K ATP ) couple intermediary metabolism to cellular activity, and may play a role in the autoregulation of vascular tones. Such a regulation requires cellular mechanisms for sensing O 2 , CO 2 , and pH. Our recent studies have shown that the pancreatic K ATP isoform (Kir6.2/SUR1) is regulated by CO 2 /pH. To identify the vascular K ATP isoform(s) and elucidate its response to hypercapnic acidosis, we performed these studies on vascular smooth myocytes (VSMs). Whole-cell and single-channel currents were studied on VSMs acutely dissociated from mesenteric arteries and HEK293 cells expressing Kir6.1/SUR2B. Hypercapnic acidosis activated an inward rectifier current that was K ϩ -selective and sensitive to levcromakalim and glibenclamide with unitary conductance of Ϸ35pS. The maximal activation occurred at pH 6.5 to 6.8, and the current was inhibited at pH 6.2 to 5.9. The cloned Kir6.1/SUR2B channel responded to hypercapnia and intracellular acidification in an almost identical pattern to the VSM current. In situ hybridization histochemistry revealed expression of Kir6.1/SUR2B mRNAs in mesenteric arteries. Hypercapnia produced vasodilation of the isolated and perfused mesenteric arteries. Pharmacological interference of the K ATP channels greatly eliminated the hypercapnic vasodilation. These results thus indicate that the Kir6.1/SUR2B channel is a critical player in the regulation of vascular tones during hypercapnic acidosis. Although these K ϩ channels are sensitive to ATP, studies have shown that they are also modulated by other nucleotides and phospholipids. [3][4][5][6][7][8][9] Previous studies have shown that K ATP channels in myocardium and insulin-secreting cell line are activated by intracellular acidification. 10,11 Similar activation was observed in the cloned pancreatic K ATP isoform (Kir6.2/ SUR1) during hypercapnic acidosis. [12][13][14][15] The regulation of K ATP by protons is particularly significant, because pH alterations occur in a large variety of physiological and pathophysiological conditions and are more frequently seen than sole energy depletion.The pH sensitivity may allow the K ATP channels to play a role in autoregulation of vascular tones. Experimental evidence suggests that the K ATP channels may be involved in reactive hyperemia, as sulfonylurea blocks hyperemic vasodilation. 16,17 The autoregulation occurs in most tissues including the heart and brain in which it underlies the cardioprotective effect of ischemic preconditioning and the activitydependent regulation of cerebral circulation. 18 -21 The reactive hyperemia is produced by hypoxia, hypercapnia, acidosis, and accumulation of other metabolic products in local tissues.Because under most physiological and pathophysiological conditions, ATP levels may not readily drop to submillimolar concentrations in cells to activate K ATP channels, 1,2 demonstration of the CO 2 /pH sensitivity of the K ATP channels becomes critical for understanding the molecular basis of the autoregulation of vascular to...

Several inward rectifier K(+) (Kir) channels are inhibited by hypercapnic acidosis and may be involved in CO(2) central chemoreception. Among them are Kir1.1, Kir2.3, and Kir4.1. The Kir4.1 is expressed predominantly in the brainstem. Although its CO(2) sensitivity is low, coexpression of Kir4.1 with Kir5.1 in Xenopus oocytes greatly enhances the CO(2)/pH sensitivities of the heteromeric channels. If these Kir channels play a part in the central CO(2) chemosensitivity, they should be expressed in neurons of brainstem cardio-respiratory nuclei. To test this hypothesis, we performed in-situ hybridization experiments in which the expression of Kir1.1, Kir2.3, Kir4.1 and Kir5.1, and coexpression of Kir4.1 and Kir5.1 were studied in brainstem neurons using non-radioactive riboprobes. We found that mRNAs of these Kir channels were present in several brainstem nuclei, especially those involved in cardio-respiratory controls. Strong labeling was observed in the locus coeruleus, ventralateral medulla, parabrachial-Kölliker-Fuse nuclei, solitary tract nucleus, and area postrema. Strong expression was also seen in several cranial motor nuclei, including the nucleus of ambiguus, hypoglossal nucleus, facial nucleus and dorsal vagus motor nucleus. In general, the expression of Kir5.1 and Kir4.1 was much more prominent than that of Kir1.1 and Kir2.3 in all the nuclei. Evidence for the coexpression of Kir4.1 and Kir5.1 was found in a good number of neurons in these nuclei. The expression and coexpression of these CO(2)/pH-sensitive Kir channels suggest that they are likely to contribute to CO(2) chemosensitivity of the brainstem neurons.

Key points• The Na + -bicarbonate cotransporter NBCe1 regulates cell and tissue pH, as well as ion movement across cell layers in organs such as kidney, gut, and pancreas.• We previously showed that the signalling molecule PIP 2 stimulates the cloned A variant of NBCe1 in a patch of biological membrane. • In the current study, we characterize the effect of injecting PIP 2 into intact oocytes expressing an NBCe1 variant (A, B, or C).• PIP 2 stimulates the B and C variants, but not the A variant, through hydrolysis to IP 3 .Stimulation requires an intracellular Ca 2+ store and kinase activity.• The results will contribute to our understanding of multiple HCO 3 − -dependent transporters with different modes of regulation, as well as how molecules that stimulate specific membrane receptors lead to changes in cell/tissue pH, and perhaps how pathologies such as stroke and ischaemia that lead to energy deficiency cause tissue acidosis. Abstract Electrogenic Na+ -bicarbonate cotransporter NBCe1 variants contribute to pH i regulation, and promote ion reabsorption or secretion by many epithelia. Most Na + -coupled bicarbonate transporter (NCBT) families such as NBCe1 contain variants with differences primarily at the cytosolic N and/or C termini that are likely to impart on the transporters different modes of regulation. For example, N-terminal regions of NBCe1 autoregulate activity. Our group previously reported that cytosolic phosphatidylinositol 4,5-bisphosphate (PIP 2 ) stimulates heterologously expressed rat NBCe1-A in inside-out macropatches excised from Xenopus laevis oocytes. In the current study on whole oocytes, we used the two-electrode voltage-clamp technique, as well as pH-and voltage-sensitive microelectrodes, to characterize the effect of injecting PIP 2 on the activity of heterologously expressed NBCe1-A, -B, or -C. Injecting PIP 2 (10 μM estimated final) into voltage-clamped oocytes stimulated NBC-mediated, HCO 3 − -induced outward currents by >100% for the B and C variants, but not for the A variant. The majority of this stimulation involved PIP 2 hydrolysis and endoplasmic reticulum (ER) Ca 2+ release. Stimulation by PIP 2 injection was mimicked by injecting IP 3 , but inhibited by either applying the phospholipase C (PLC) inhibitor U73112 or depleting ER Ca 2+ with prolonged thapsigargin/EGTA treatment. Stimulating the activity of store-operated Ca 2+ channels (SOCCs) to trigger a Ca 2+ influx mimicked the PIP 2 /IP 3 stimulation of the B and C variants. Activating the endogenous G q protein-coupled receptor in oocytes with lysophosphatidic acid (LPA) also stimulated the B and C variants in a Ca on NBCe1-C-expressing oocytes, LPA increased the NBC-mediated pH i -recovery rate from a CO 2 -induced acid load by ∼80%. Finally, the general kinase inhibitor staurosporine completely inhibited the IP 3 -induced stimulation of NBCe1-C. In summary, injecting PIP 2 stimulates the activity of NBCe1-B and -C expressed in oocytes through an increase in IP 3 /Ca 2+ that involves a staurosporine-sensitive kinase. In ...