The human tandem P domain K+ channel hTREK-1 (KCNK2) is distributed widely through the CNS. Here, whole-cell patch clamp recordings were employed to investigate the effects of hypoxia on hTREK-1 channels stably expressed in human embryonic kidney cells. Acute hypoxia caused a rapid and reversible inhibition of whole-cell K+ current amplitudes; this was PO2 dependent with a maximal inhibition achieved at 60 mmHg and below. In accordance with previous studies, hTREK-1 current amplitudes were enhanced by arachidonic acid. This effect was concentration dependent, with maximal enhancement observed at a concentration of 10 microM. Membrane deformation by the crenator trinitrophenol (to mimic cell swelling) or the cup former chlorpromazine (to mimic cell shrinkage) caused robust activation and inhibition of currents, respectively. However, current augmentation by either arachidonic acid or trinitrophenol was completely prevented during hypoxia; conversely, hypoxia blunted the inhibitory action of chlorpromazine. The abilities of arachidonic acid to augment currents and of hypoxia to completely abrogate this effect were also observed in cell-attached patches. Our data indicate that hypoxia interacts with hTREK-1, and occludes its modulation by arachidonic acid and membrane deformation. These findings also suggest that the potential neuroprotective role of TREK channels, which has recently been proposed, requires reconsideration since hTREK-1 activation is unlikely when ambient PO2 is below 60 mmHg - a situation which normally pertains in the CNS even during systemic normoxia.

Miller, Paula, Chris Peers, and Paul J. Kemp. Polymodal regulation of hTREK1 by pH, arachidonic acid, and hypoxia: physiological impact in acidosis and alkalosis. Am J Physiol Cell Physiol 286: C272-C282, 2004. First published October 1, 2003 10.1152/ ajpcell.00334.2003.-Expression of the human tandem P domain K ϩ channel, hTREK1, is limited almost exclusively to the central nervous system, where ambient PO 2 can be as low as 20 Torr. We have previously shown that this level of hypoxia evokes a maximal inhibitory influence on recombinant hTREK1 and occludes the activation by arachidonic acid; this has cast doubt on the idea that TREK1 activation during brain ischemia could facilitate neuroprotection via hyperpolarizing neurons in which it is expressed. Using both whole cell and cell-attached patch-clamp configurations, we now show that the action of another potent TREK activator and ischemia-related event, intracellular acidification, is similarly without effect during compromised O2 availability. This occlusion is observed in either recording condition, and even the concerted actions of both arachidonic acid and intracellular acidosis are unable to activate hTREK1 during hypoxia. Conversely, intracellular alkalinization is a potent channel inhibitor, and hypoxia does not reverse this inhibition. However, increases in intracellular pH are unable to occlude either arachidonic acid activation or hypoxic inhibition. These data highlight two important points. First, during hypoxia, modulation of hTREK1 cannot be accomplished by parameters known to be perturbed in brain ischemia (increased extracellular fatty acids and intracellular acidification). Second, the mechanism of regulation by intracellular alkalinization is distinct from the overlapping structural requirements known to exist for regulation by arachidonic acid, membrane distortion, and acidosis. Thus it seems likely that hTREK1 regulation in the brain will be physiologically more relevant during alkalosis than during ischemia or acidosis. potassium channel; tandem P domain THE TANDEM P DOMAIN potassium channel TREK1 is localized almost exclusively to the central nervous system (CNS), where it is believed to play a key role in setting the resting membrane potential of the neurons in which it is expressed (4,12,16,17). Evidence also exists for its expression in the peripheral nervous system, in general and sensory neurons of the dorsal root ganglion in particular (12). On the basis of the ability of TREK to influence the resting membrane potential of neurons, coupled to evidence of its specific regulation by unsaturated fatty acids (4, 15, 23), membrane stretch (23), acidosis (12, 13), and inhalation anesthetics (22), it has been suggested that this background K ϩ channel may control neuronal excitability and play a neuroprotective role during brain ischemia, where local pH declines and arachidonic acid is released into the extracellular space (see, for example, Ref. 24). Further support for such an idea has come from the demonstration that the neuroprotecti...

The combination of studies in native tissues and immortalised model systems during the last decade has made possible a deeper understanding of the physiology and functional morphology of arterial and airway oxygen sensors. Complementary and overlapping information from these earlier studies has allowed a detailed description of the cellular events that link decreased environmental oxygen to the release of physiologically important vasoactive transmitters. Since these basic pathways have now been defined functionally, what remains to be determined is the molecular identity of the specific proteins involved in the signal transduction pathways, and how these proteins interact to produce a full physiological response. With these goals clearly in sight, we have embarked upon a strategy that is a novel combination of proteomics and functional genomics. It is hoped this strategy will enable us to develop and refine the initial models in order to understand more completely the process of oxygen sensing in health and disease. Anat Rec Part A 270A: 41-50, 2003.

Mares of mixed breeding (379 to 594 kg) were injected intramuscularly once with Prostin F2 alpha | (PGF20t) in doses ranging between 0 and 10 mg between days 6 and 9 after ovulation. Prostaglandin F2a caused luteolysis as measured by reduction in intervals between injection and either return to estrus or ovulation and by reduction in interovulatory intervals for four of eight, seven of nine, eight of nine, four of eight, seven of nine and eight of eight mares treated with .25, 1, 2.5, 3, 5 or 10 mg PGF2a, respectively. Duration for both estrus and the estrous cycle subsequent to administration of Prostin F2 alpha was within the range accepted as normal indicating no carryover effects of treatment. Sweating was not observed for mares treated with .25 mg PGF2a but was observed for mares treated with 1, 2.5, 3, 5 or 10 mg between 1/4 and 2 hr after injection. Most mares had ceased sweating within 1 hr after injection, but drying was not completed for up to 3 to 5 hr after injection. Rectal temperature was decreased significantly during the intervals 1/2 through 1, 1/2 through 4, 1/2 through 3", 1/2 through 5, or 1/4 through 5 hr after treatment of mares with 1, 2.5, 3, 5 or 10 mg PGF2a, respectively. Compared to appropriate controls, maximum temperature decrease of mares was on the order of .5 to .6 C for those treated with .25 or 1 mg, .9 to 1.2 C for those treated with 2.5, 3, or 5 mg, and 1.7 C for those treated with 10 mg PGF2a. Decreases in rectal temperature were associated with sweating and drying. Neither heart nor respiration rates were 1 Agricultural Research and Development. A portion of these data were presented at the 1975 A.S.A.S. meeting, Colorado State University. 2The authors express appreciation to E.

The tandem P domain potassium channels, TREK1 and TASK1, are expressed throughout the brain but expression patterns do not significantly overlap. Since normal pO 2 in central nervous tissue is as low as 20 mmHg and can decrease even further in ischemic disease, it is important that the behaviour of human brain ion channels is studied under conditions of acute and chronic hypoxia. This is especially true for brain-expressed tandem P-domain channels principally because they are important contributors to neuronal resting membrane potential and excitability. Here, we discuss some recent data derived from two recombinant tandem P-domain potassium channels, hTREK1 and hTASK1. Hypoxia represents a potent inhibitory influence on both channel types and occludes the activation by arachidonic acid, intracellular acidosis and membrane deformation of TREK1. This casts doubt on the idea that TREK1 activation during brain ischemia might facilitate neuroprotection via hyperpolarising neurons in which it is expressed. Interestingly, hypoxia is unable to regulate alkalotic inhibition of TREK1 suggesting that this channel may be more intimately involved in control of excitability during physiological or pathological alkalosis.