Ten year performance evaluation of a field-scale zero-valent iron permeable reactive barrier installed to remediate trichloroethene contaminated groundwater.

The Monkstown zero-valent iron permeable reactive barrier (ZVI PRB), Europe's oldest commercially-installed ZVI PRB, had been treating trichloroethene (TCE) contaminated groundwater for about 10 years on the Nortel Network site in Northern Ireland when cores from the reactive zone were collected in December, 2006. Groundwater data from 2001-2006 indicated that TCE is still being remediated to below detection limits as the contaminated groundwater flows through the PRB. Ca and Fe carbonates, crystalline and amorphous Fe sulfides, and Fe (hydr)oxides have precipitated in the granular ZVI material in the PRB. The greatest variety of minerals is associated with a approximately 1-2 cm thick, slightly cemented crust on top (up-gradient influent entrance) of the ZVI section of the PRB and also with the discontinuous cemented ZVI material ( approximately 23 cm thick) directly below it. The greatest presence of microbial communities also occurred in the up-gradient influent portion of the PRB compared to its down-gradient effluent section, with the latter possibly due to less favorable conditions (i.e., high pH, low oxygen) for microbial growth. The ZVI filings in the down-gradient effluent section of the PRB have a projected life span of >10 years compared with ZVI filings from the continuous to discontinuous cemented up-gradient ZVI section (upper approximately 25 cm) of the PRB, which may have a life span of only approximately 2-5 more years. Supporting Information from applied, multi-tracer testing indicated that restricted groundwater flow is occurring in the upper approximately 25 cm of the ZVI section and preferential pathways have also formed in this PRB over its 10 years of operation.

cAMP-regulated whole cell chloride currents in pancreatic duct cells.

Using the whole cell configuration of the patch-clamp technique, we have identified an adenosine 3',5'-cyclic monophosphate (cAMP)-regulated chloride conductance in pancreatic duct cells. Basal whole cell currents in single isolated cells were very low (approximately 5 pA/pF) but could be stimulated 17-fold by elevation of intracellular cAMP. The cAMP-activated currents exhibited 1) a high chloride selectivity, 2) a near linear current-voltage relationship, 3) time and voltage independence, 4) block by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) but not by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 5) an anion selectivity sequence based on permeability ratios of SCN > NO3 > Br > Cl > I > HCO3 > F > ClO4 > gluconate. Currents in single cells ran down within a few minutes; however, stable chloride currents could be recorded from duct cell clusters in which four or five cells were in electrical communication. We present evidence suggesting that these cAMP-regulated currents are carried by cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels. Physiologically, these CFTR channels act in parallel with chloride-bicarbonate exchangers to facilitate bicarbonate secretion across the apical plasma membrane of the duct cell.

A potassium current evoked by growth hormone-releasing hormone in follicular oocytes of Xenopus laevis.

1. Electrophysiological properties of the growth hormone-releasing hormone (GRH) receptor were studied in Xenopus oocytes with an intact follicle cell layer (i.e. follicular oocytes) by measuring whole-cell current using the two-electrode voltage-clamp method. 2. A slow transient outward current was elicited in oocytes, clamped at -60 mV, by the application of rat GRH but not bovine, porcine, or human GRH. 3. The response to GRH was not suppressed by blockers known to inhibit other endogenous receptors present in follicular Xenopus oocytes; blockers used were timolol (2 microM; beta-adrenergic blocker), theophylline (0.1 mM; purinergic blocker) and atropine (100 nM; muscarinic blocker). 4. The current response evoked by rat GRH occurred in a dose-dependent manner. The concentrations of GRH for threshold and maximum responses were 1 and 100 nM respectively and the estimated EC50 (half-maximal effective concentration) was approximately 7 nM. The amplitude and conductance of the response became larger and the latency, time-to-peak and half-decay time were shortened when the concentration of GRH was increased. 5. The GRH response was reversibly inhibited by a K+ channel blocker, tetraethylammonium+ (TEA+; 20 mM). The reversal potential for the GRH response was around -100 mV and was compatible with the reported value for a K+ current in Xenopus oocytes. Furthermore, a depolarizing shift of 40 mV in the reversal potential was observed when the external K+ concentration was increased from 2 to 10 mM, agreeing with the Nernst equation. In contrast, no significant shift in the reversal potential was observed by changing the external concentration of Na+ or Cl-. 6. The GRH response was not suppressed in oocytes treated with an acetoxy-methyl ester of bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA/AM; 10 microM) which penetrates the cell membrane and chelates internal Ca2+. 7. The GRH response was potentiated by pre-treatment with forskolin (0.4 microM; 5 min), which stimulates adenylate cyclase and increases the internal concentration of adenosine 3',5'-cyclic monophosphate (cyclic AMP). 8. The GRH response was not obtainable when follicle cells surrounding oocytes were removed mechanically with forceps or enzymically with collagenase (i.e. denuded oocytes). The response was also suppressed when gap junctions, which electrically couple follicle cells and the oocyte, were blocked by 1-octanol (1 mM). 9. The first amino acid is considered to be important for the binding of peptide ligands to their receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Single Ca2(+)-activated K+ channels in excised membrane patches of hamster oocytes.

The properties of the Ca2(+)-activated K+ channel in unfertilized hamster oocytes were investigated at the single-channel level using inside-out excised membrane patches. The results indicate a new type of Ca2(+)-activated K+ channel which has the following characteristics: (1) single-channel conductance of 40-85 pS for outward currents in symmetrical K+ (150 mM) solutions. (2) inward currents of smaller conductance (10-50 pS) than outward currents, i.e. the channel is outwardly rectified in symmetrical K+ solutions, (3) channel activity dependent on the internal concentration of free Ca2+ and the membrane potential, (4) modification of the channel activity by internal adenosine 5' diphosphate (0.1 mM) producing a high open probability regardless of membrane potential.

Chloride channels mediate the response to gonadotropin-releasing hormone (GnRH) in Xenopus oocytes injected with rat anterior pituitary mRNA.

Functional expression of receptors for GnRH was studied using Xenopus laevis oocytes injected with poly(A)+ mRNA extracted from rat anterior pituitary glands. Whole-cell currents were monitored using two-electrode voltage-clamp techniques. In oocytes which responded to both GnRH and TRH, the GnRH response showed a longer latency and time-to-peak than the TRH response. The response to GnRH or an agonist of GnRH receptors, buserelin (1 nM-1 microM) consisted of current fluctuations and occurred in a dose-dependent manner. This GnRH response was blocked by the Cl- channel blockers 9-AC (9-anthracene carboxylic acid; 1 mM), 4,4'-diisothiocyanastilbene-2,2'-disulfonic acid (0.1 mM), and diphenylamine-2-carboxylic acid (0.1 mM). The reversal potential for the GnRH-induced current fluctuations was -25 mV, comparable with the reported Cl- equilibrium potential in Xenopus oocytes, and its shift, when the external concentration of Cl- was changed, was reasonably described by the Nernst equation. These results indicate that the GnRH-induced response was dependent on the activity of Cl- channels. Ca2+ also plays a role, as the GnRH-induced response was reversibly suppressed by a calmodulin inhibitor, chlordiazepoxide (0.2 microM), and by a blocker of intracellular Ca2+ release, TMB-8 (8-(N.N-diethylamino) octyl-3,4,5-trimethoxybenzoate; 0.1-0.2 mM). It is concluded that GnRH (and TRH) receptors, expressed in Xenopus oocytes by injecting exogenous mRNA from rat anterior pituitary glands, operate via activation of Ca2+-dependent Cl- channels.

Functional expression of rat pituitary gonadotrophin-releasing hormone receptors in Xenopus oocytes.

Expression of receptors for the hypothalamic regulatory peptide, gonadotrophin-releasing hormone (GnRH), was investigated by intracellular recording from Xenopus oocytes injected with poly(A)+ mRNA isolated from rat anterior pituitary glands. Membrane depolarizations were induced in oocytes in a dose-dependent fashion following the application of GnRH (10nM - 1 microM) or a GnRH superactive agonist, buserelin (1nM - 1 microM). The response was reversibly blocked by the addition of a GnRH antagonist (1 microM). TRH (10nM - 1 microM) had no effect on most of these oocytes. In contrast, some other oocytes which showed no responses to GnRH or to the GnRH agonist, displayed depolarizing responses to TRH (10nM - 1 microM). A relatively small number of oocytes responded to both ligands. Control oocytes did not respond to the GnRH analogues or to TRH. This successful expression of the GnRH receptor could provide a new approach to the study of the receptor, and serve as a means for the isolation and cloning of the encoding genes.

cAMP response of vascular smooth muscle cells to bovine parathyroid hormone.

Parathyroid hormone (PTH) is a vasodilator of vascular smooth muscle tissue. It has been shown to produce this vasodilation in normotensive and hypertensive laboratory rats. The effect is log dose dependent, maximal at 1 min and persists for 3-5 min. The cellular mechanisms involved in PTH-mediated vasodilation are unknown. In this study, we sought to determine the cellular changes of cAMP after administration of bovine (b)PTH (1-34). cAMP content of vascular smooth muscle cells was measured at 30 s, 1, 3, and 5 min after incubation with synthetic bPTH (1-34). Tissue cAMP content was decreased by 55% at 1 min (4.1 +/- 0.5 pmol/mg protein at time 0 vs. 1.9 +/- 0.2 pmol/mg protein at 1 min, P less than 0.001). After 5 min, cAMP levels returned to base-line values and increased over the next 5-10 min to levels above base line (P less than 0.01). In conclusion, our data suggest that the initial response of vascular smooth muscle cells to short-term incubation with bPTH (1-34) is an acute decrease in cAMP content.