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P S Jackson

Publications and source records attributed to P S Jackson.

At least 19 recordsLinked to original sources
PubMed1997

Identification of the volume-sensitive organic osmolyte/anion channel in human glial cells.

Cellular use of small organic solutes known as organic osmolytes for regulation of the volume of the cell is a universal biological phenomenon. During swelling, cells open an anion channel which allows for efflux of these solutes. This channel is known as the volume-sensitive organic osmolyte/anion channel (VSOAC). Anion channels with properties identical to VSOAC were found in human brain cells obtained following pediatric neurosurgical procedures. The tissues examined included tumors as well as putatively normal gray and white matter astrocytes. The cells activated an anion conductance when swollen by hypotonic shock. Baseline currents in these cells were generally small and increased up to 30-fold within 10 min following the onset of swelling. The anion channel activated by swelling was outwardly rectified and inactivated by depolarization, both characteristic of the VSOAC. These observations indicate that human glial cells and tumor cells activate VSOAC following cellular swelling. This suggests that organic osmolyte efflux can be modulated during brain swelling by pharmaceuticals which modulate VSOAC.

Anion Transport Proteins↗
PubMed1996

Single channel properties of a volume sensitive anion channel: lessons from noise analysis.

Swelling activated anion channels have recently been recognized to play an important role in not only volume regulatory electrolyte movement, but also in organic osmolyte transport. A swelling-activated, outwardly rectifying anion channel termed VSOAC (volume-sensitive organic osmolyte/anion channel) is a major pathway for swelling-induced loss of organic osmolytes and organic anions from mammalian cells. VSOAC has been described in numerous cell types. Until recently, however, the unitary conductance and gating kinetics of VSOAC were uncertain. Stationary noise analysis and single channel measurements have produced estimates for the unitary conductance of swelling-activated, outwardly rectifying anion channels that vary by > 15-fold. This review describes our current understanding of the single channel properties of VSOAC.

Animals↗
PubMed1996

Swelling-activated anion conductance in skate hepatocytes: regulation by cell Cl- and ATP.

Cell swelling activates an outwardly rectifying anion conductance in mammalian cells. The channel responsible for this conductance mediates volume-regulatory efflux of organic osmolytes such as taurine. We observed a similar conductance in hepatocytes from the skate Raja erinacea. Whole cell Cl- conductance was increased > 100-fold by a 2-fold increase in hepatocyte volume. The conductance was outwardly rectifying and had a relative cation permeability of approximately 0.2. Cation permeability was increased by reductions in patch pipette CsCl concentration, suggesting that the channel pore contains saturable anion and cation binding sites with different anion and cation affinities. The conductance had a broad anion selectivity and a relative taurine permeability of 0.17. Activation of the conductance required intracellular ATP or a nonhydrolyzable ATP analogue. Elevation of intracellular Cl- from 20 to 155 mM reduced current activation while the rate and extent of cell swelling were unaffected. Reduction of intracellular Cl- concentration to 5-10 mM caused spontaneous current activation without cell swelling. These results suggest that increases in cell Cl- levels increase the volume set point of the channel. We propose that the main function of the outwardly rectifying anion channel is nonselective transport of organic solutes.

Adenosine Triphosphate↗
PubMed1996

Cellular and molecular physiology of volume-sensitive anion channels.

Maintenance of a constant cell volume in the face of osmotic stress is an evolutionarily ancient homeostatic process. Over the last two decades physiologists have gained an impressive understanding of the "volume-sensitive" channels, cotransporters, exchangers, metabolic pathways, and genes that are responsible for modulating intracellular solute content and cell volume. This review focuses on one part of this story, the characteristics and osmoregulatory functions of volume-sensitive anion channels. Three distinct types of swelling-activated anion channels have been observed and studied extensively in animal cells. These channels include 1) ClC-2, which is a member of the ClC family of voltage-gated anion channels, 2) an outwardly rectifying intermediate conductance channel, and 3) a large-conductance or "maxi" channel. In addition to these three channels, several other less well-characterized anion channels have been observed. This review discusses the electrophysiological and molecular biological characteristics and regulation of these channels. The possible roles different types of anion channels might play in cell volume homeostasis are also discussed.

Amino Acid Sequence↗
PubMed1995

Performance prediction for Olympic kayaks.

This paper sets out the effects of the various factors which determine the speed of racing kayaks and canoes, with the aim of identifying the areas most likely to lead to improvements. The friction, wave and aerodynamic components of hull drag are first described in terms of the hull parameters, in order to provide accurate predictions of propulsive power as a function of hull speed. The generation of thrust by paddling is described via the mechanics of vortex-ring wakes, in order to determine the propulsive efficiency in terms of the parameters describing the blade and stroke. Equating the thrust and drag then leads to reliable estimates of the mechanical power actually delivered by a canoeist. The earlier analysis then leads to a predictive model for hull speed in terms of all the parameters describing the hull and blade performance. This is used to determine the sensitivity of hull speed to small changes in each parameter, enabling the most important factors to be identified. The paper concludes with a discussion of the various improvements to kayaks that have actually appeared in recent years, and uses the earlier analysis to explain and predict the resulting speed changes.

Biophysical Phenomena↗
PubMed1995

Single-channel properties of a volume-sensitive anion conductance. Current activation occurs by abrupt switching of closed channels to an open state.

Swelling-induced loss of organic osmolytes from cells is mediated by an outwardly rectified, volume-sensitive anion channel termed VSOAC (Volume-Sensitive Organic osmolyte/Anion Channel). Similar swelling-activated anion channels have been described in numerous cell types. The unitary conductance and gating kinetics of VSOAC have been uncertain, however. Stationary noise analysis and single-channel measurements have produced estimates for the unitary conductance of swelling-activated, outwardly rectified anion channels that vary by > 15-fold. We used a combination of stationary and nonstationary noise analyses and single-channel measurements to estimate the unitary properties of VSOAC. Current noise was analyzed initially by assuming that graded changes in macroscopic current were due to graded changes in channel open probability. Stationary noise analysis predicts that the unitary conductance of VSOAC is approximately 1 pS at 0 mV. In sharp contrast, nonstationary noise analysis demonstrates that VSOAC is a 40-50 pS channel at +120 mV (approximately 15 pS at 0 mV). Measurement of single-channel events in whole-cell currents and outside-out membrane patches confirmed the nonstationary noise analysis results. The discrepancy between stationary and nonstationary noise analyses and single-channel measurements indicates that swelling-induced current activation is not mediated by a graded increase in channel open probability as assumed initially. Instead, activation of VSOAC appears to involve an abrupt switching of single channels from an OFF state, where channel open probability is zero, to an ON state, where open probability is near unity.

Animals↗
PubMed1995

Characterization of the voltage-dependent properties of a volume-sensitive anion conductance.

Outwardly rectified, swelling-activated anion conductances have been described in numerous cell types. The major functional variable observed amongst these conductances is the extent and rate of depolarization-induced inactivation. In general, the conductances can be divided into two broad classes, those that show rapid inactivation in response to strong depolarization and those that show little or no voltage dependence. The swelling-activated anion conductance in rat C6 glioma cells is inactivated nearly completely by membrane depolarization above +90 mV and reactivated by membrane hyperpolarization. The kinetics of inactivation and reactivation are fit by single and double exponentials, respectively. Voltage-dependent behavior is well described by a simple linear kinetic model in which the channel exists in an open or one of three inactivated states. pH-induced changes in voltage-dependent gating suggest that the voltage sensor contains critical basic amino acid residues. Extracellular ATP blocks the channel in a voltage-dependent manner. The block is sensitive to the direction of net Cl- movement and increases open channel noise indicating that ATP interacts with the channel pore. Blockage of the channel with ATP dramatically slows depolarization-induced inactivation.

Adenosine Triphosphate↗
PubMed1995

ATP depletion and inactivation of an ATP-sensitive taurine channel by classic ion channel blockers.

Cell volume regulation in different cell types is mediated in part by plasma membrane channel(s) that allow taurine and other important intracellular organic osmolytes to efflux from the cell. Previous studies have demonstrated that intracellular ATP is required for activation of a volume-sensitive taurine-permeable channel. The present study examined the relation between cellular ATP and ADP concentrations and swelling-induced [14C]taurine efflux and anion current (whole-cell patch-clamp) after exposure of isolated skate (Raja erinacea) hepatocytes to metabolic poisons and a series of ion channel blockers. When intracellular ATP content was lowered with gradually increasing concentrations of 2,4-dinitrophenol, a sigmoidal relation between ATP content and volume-activated [14C]taurine efflux was observed. Taurine efflux was progressively inhibited over a relatively narrow range of intracellular ATP levels, indicating that physiologic alterations in cellular nucleotides may modulate the opening of the channel. Surprisingly, the inhibition of [14C]taurine efflux by a number of ion channel blockers [glibenclamide, 5-nitro-2-(3-phenylpropylamino)benzoate, diphenylamine-2-carboxylate, ketoconazole, gossypol, niflumic acid, and quinine] was related to a decrease in cellular ATP concentrations and ATP/ADP ratios, rather than to a direct interaction with the channel. In contrast, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid and pyridoxal-5-phosphate inhibited volume-activated anion channels but had no effect on cellular ATP levels. These findings suggest multiple sites for regulation of volume-sensitive osmolyte channels and indicate that some putative ion channel blockers may actually alter the activity of ATP-regulated transporters by depleting cellular ATP.

2,4-Dinitrophenol↗
PubMed1995

Two factors secreted by the goldfish optic nerve induce retinal ganglion cells to regenerate axons in culture.

Unlike mammals, lower vertebrates can regenerate an injured optic nerve and other pathways of the CNS throughout life. We report here that in dissociated cell culture, goldfish retinal ganglion cells regenerate their axons in response to two factors derived from the sheath cells of the optic nerve. Axogenesis factor 1 (AF-1) is a small peptide (700-900 Da) that is inactivated by treatment with proteinase K but heat stable. A second factor, AF-2, is a polypeptide of ca 12 kDa. In the absence of these factors, dissociated retinal cells remained viable in serum-free, defined media for at least a week but showed little outgrowth, as visualized using the vital dye 5,6-carboxyfluorescein diacetate (5,6-CFDA). The addition of AF-1 induced up to 25% of cells in culture to extend processes > 75 microns in length by 6 d; AF-2 had a lesser but highly significant effect. To verify that neurite outgrowth was from retinal ganglion cells per se, we applied the lipophilic dye 4-Di-10-ASP to the optic tectum and allowed it to diffuse up the optic nerve for several days before culturing the retina. A far greater percentage of cells containing the dye showed axonal outgrowth than was observed from the overall cell population, indicating that ganglion cells are selective targets of the factors. The effects of AF-1 or AF-2 were not secondary to enhanced viability, since neither overall cell survival nor the number of retinal ganglion cells remaining in culture after 6 d was affected by the presence of the factors. The activity of AF-1 and AF-2 was not mimicked by several defined factors tested over a broad concentration range, for example, NGF, BDNF, NT-3, CNTF, taurine, retinoic acid, acidic or basic fibroblast growth factors. The concentration of AF-1 is considerably higher in CM than in optic nerve homogenates, suggesting that it is actively secreted; AF-2 has a similar concentration intra- and extracellularly. Insofar as AF-1 and AF-2 derive from cells of the optic nerve and act upon retinal ganglion cells, they are likely to be important in inducing optic nerve regeneration in vivo.

Animals↗
PubMed1994

The volume-sensitive organic osmolyte-anion channel VSOAC is regulated by nonhydrolytic ATP binding.

Efflux of intracellular organic osmolytes to the external medium is a ubiquitous response to cell swelling. Accumulating evidence indicates that volume regulatory loss of structurally unrelated organic osmolytes from cells is mediated by a relatively nonselective volume-sensitive anion channel. In C6 cells, we have termed this channel VSOAC for volume-sensitive organic osmolyte-anion channel. Swelling-induced activation of VSOAC required the presence of ATP or nonhydrolyzable ATP analogues [adenosine 5'-O-(3-thiotriphosphate), adenylylmethyl-enediphosphonate (AMP-PCP), or 5'-adenylylimidodiphosphate] in the patch pipette. Sustained activation of VSOAC also required ATP. Channel rundown was observed when cellular ATP levels were lowered by intracellular dialysis with the patch pipette solution. Rundown was prevented by the ATP analogue AMP-PCP. Passive swelling-induced myo-[3H]inositol and [3H]taurine efflux was blocked by metabolic inhibitors that decreased cellular ATP levels. Titration of cellular ATP levels with azide demonstrated that the apparent dissociation constant (Kd) for ATP of both myo-inositol and taurine efflux was approximately 1.7 mM. The high Kd for ATP indicates that cellular metabolic state plays an important role in modulating organic osmolyte loss. Regulation of VSOAC activity by ATP prevents depletion of metabolically expensive organic osmolytes when cellular energy production is reduced. In addition, ATP-dependent regulation provides essential feedback to minimize the loss of energy-producing carbon sources such as pyruvate, short-chain fatty acids, ketone bodies, and amino acids, which readily permeate this channel.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Volume-sensitive anion channels mediate swelling-activated inositol and taurine efflux.

C6 glioma cells accumulate the organic osmolyte inositol in response to chronic hypertonic stress. Upon return to isotonic conditions, cell swelling activates a Na(+)-independent passive low-affinity inositol efflux mechanism that is inhibited 80-100% by a number of anion transport blockers, certain lipoxygenase blockers, and various polyunsaturated fatty acids. Taurine efflux is also enhanced by cell swelling. The taurine efflux pathway has characteristics that are identical to those of the inositol efflux mechanism, including kinetics of activation and inactivation, osmotic sensitivity, pharmacological sensitivity, and inhibition by certain Na+ and Cl- substitutes. These results suggest strongly that volume-sensitive inositol and taurine efflux are mediated by a common transport mechanism. The inhibition of the transport pathway by anion transport blockers and unsaturated fatty acids suggests indirectly that efflux of these solutes may be mediated by an anion channel. Whole cell patch clamp measurements in CsCl solutions were used to test this hypothesis. Under hypertonic conditions, C6 cells had an extremely low membrane conductance (approximately 0.02 nS/pF). After cell swelling, however, whole cell anion conductance was activated rapidly to values up to 1.5-2 nS/pF. This conductance was outwardly rectified and selective for anions and was inhibited 80-100% by blockers of swelling-activated inositol and taurine efflux. The relative taurine permeability (i.e., Ptaurine/PCl) of the conductance was 0.20. Isosmotic replacement of raffinose in the external medium with inositol or sorbitol induced a transient inward current, suggesting that Cl- and these polyols compete for common binding sites on the channel. We conclude that a volume-sensitive anion channel mediates the efflux of structurally diverse organic osmolytes such as taurine and inositol from the cell.

Animals↗
PubMed1993

Stereotypical changes in the pattern and duration of long-term potentiation expressed at postnatal days 11 and 15 in the rat hippocampus.

1. Extracellular recordings from hippocampal area CA1 lasting 2-8 h posttetanus were used to evaluate the duration of long-term potentiation (LTP) at two key developmental ages. 2. At day 11 LTP consistently endured for approximately 1 h before declining to baseline by 2.5 h posttetanus. The response could then be repotentiated, and in some cases, the repotentiation lasted longer than the original potentiation. 3. At day 15 two patterns of potentiation were observed. The first pattern was similar to that observed at day 11 in that the potentiation did not persist; however, it did endure for approximately 2-2.5 h before declining to baseline by 4 h posttetanus. In the second pattern the potentiation persisted indefinitely; these responses were monitored for 6-8 h posttetanus. 4. These patterns are similar to the temporal phases of LTP that have been revealed in adult rat hippocampus through pharmacological manipulations. They may reflect developmental changes during which the different cellular mechanisms underlying LTP become sequentially activated. 5. These findings are important for several reasons. First, because the different temporal phases of LTP seem to be added stepwise during development, animals of different ages could be used explicitly to elucidate the underlying cellular mechanisms of these phases in LTP. Second, because LTP is a candidate mechanism for some forms of learning and memory, these results have implications for sequential steps in the ontogeny of learning and memory. Finally, because studies of LTP have used animals of widely varying ages, including these two ages, it is important to consider whether differences in the developmental properties of LTP could influence experimental observations.

2-Amino-5-phosphonovalerate↗
PubMed1991

GDP beta S antagonizes whole-cell current responses to excitatory amino acids.

Guanine nucleotides have been predicted to be NMDA antagonists in tissue binding studies. Using the patch-clamp technique, we now show that the guanine nucleotide GDP beta S produces a rapidly reversible antagonism of NMDA, kainate, and, less potently, quisqualate whole-cell current responses. Furthermore, it does not appear that this antagonism is effected intracellularly. Our results suggest a novel extracellular role for guanine nucleotides apart from their traditional intracellular actions on G-proteins.

Animals↗
PubMed1985

Analysis of nucleoproteins by direct injection of dissolved nuclei or chromosomes into a high-performance liquid chromatographic system.

This work describes the development of a method for fractionating the total nuclear proteins of Chinese hamster cells (line CHO) by high-performance liquid chromatography of whole nuclei or chromosomes. Nuclei or chromosomes were dissolved for 2 h in 6 M guanidine hydrochloride containing 0.2% trifluoroacetic acid (TFA). Residual particulates were removed by centrifugation, and a sample of the solution was passed through a Bio-Sil TSK guard column, followed by a Bio-Sil TSK 400 column, equilibrated with water containing 0.2% TFA. These columns fractionated the sample by adsorbing the DNA, passing the proteins near the exclusion limit, passing the guanidine at the inclusion limit, and passing an unidentified non-protein/non-DNA material after the inclusion limit. The protein peaks from the TSK columns were collected directly on a muBondapak CN reversed-phase column. The protein fractions were then eluted from the CN column with an acetonitrile gradient containing 0.2% TFA. Three other reversed-phase columns were examined for use with the TSK columns. The muBondapak C18 Radial-Pak column produced the best resolution of histone variants, while the Zorbax C8 column produced a better resolution of the non-histone proteins. The Nova-Pak C18 Radial-Pak column was found to be unsatisfactory for both classes of nucleoproteins.

Animals↗