First Direct Measurements of Superheavy-Element Mass Numbers.

An experiment was performed at Lawrence Berkeley National Laboratory's 88-in. Cyclotron to determine the mass number of a superheavy element. The measurement resulted in the observation of two α-decay chains, produced via the ^{243}Am(^{48}Ca,xn)^{291-x}Mc reaction, that were separated by mass-to-charge ratio (A/q) and identified by the combined BGS+FIONA apparatus. One event occurred at A/q=284 and was assigned to ^{284}Nh (Z=113), the α-decay daughter of ^{288}Mc (Z=115), while the second occurred at A/q=288 and was assigned to ^{288}Mc. This experiment represents the first direct measurements of the mass numbers of superheavy elements, confirming previous (indirect) mass-number assignments.

0(gs)+ -->2(1)+ transition strengths in 106Sn and 108Sn.

The reduced transition probabilities, B(E2; 0(gs)+ -->2(1)+), have been measured in the radioactive isotopes (108,106)Sn using subbarrier Coulomb excitation at the REX-ISOLDE facility at CERN. Deexcitation gamma rays were detected by the highly segmented MINIBALL Ge-detector array. The results, B(E2;0(gs)+ -->2(1)+)=0.222(19)e2b2 for 108Sn and B(E2; 0(gs)+-->2(1)+)=0.195(39)e2b2 for 106Sn were determined relative to a stable 58Ni target. The resulting B(E2) values are approximately 30% larger than shell-model predictions and deviate from the generalized seniority model. This experimental result may point towards a weakening of the N=Z=50 shell closure.

Measurement of the sign of the spectroscopic quadrupole moment for the 2(1)+ state in 70Se: no evidence for oblate shape.

Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of 70Se ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation gamma rays in the highly segmented MINIBALL gamma-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first 2+ state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first 2+ state in 70Se, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes.

The impact of rainstorm events on coagulation and clarifier performance in potable water treatment.

This paper examines turbidity removal at a water treatment works in England that receives raw water which is difficult to treat during certain rainstorm events. Rainstorm events lead to elevated levels of turbidity and organic matter found in river waters. A robustness index based on settled turbidity was used to identify periods and events that adversely affected the treatment process. This coupled with raw water sampling data indicated that a change in nature and an increase in natural organic matter (NOM) concentrations occurred following rainstorm events. Experimental work investigated the effect of temperature and NOM on the coagulation process and the results show how increasing levels of NOM significantly impaired the coagulation of particulate material, leading to an increase in settled turbidity.

Activation of maxi-K channels by parathyroid hormone and prostaglandin E2 in human osteoblast bone cells.

Patch clamp experiments were performed on two human osteosarcoma cell lines (MG-63 and SaOS-2 cells) that show an osteoblasticlike phenotype to identify and characterize the specific K channels present in these cells. In case of MG-63 cells, in the cell-attached patch configuration (CAP) no channel activity was observed in 2 mM Ca Ringer (control condition) at resting potential. In contrast, a maxi-K channel was observed in previously silent CAP upon addition of 50 nM parathyroid hormone (PTH), 5 nM prostaglandin E2 (PGE2) or 0.1 mM dibutyryl cAMP + 1 microM forskolin to the bath solution. However, maxi-K channels were present in excised patches from both stimulated and nonstimulated cells in 50% of total patches tested. A similar K channel was also observed in SaOS-2 cells. Characterization of this maxi-K channel showed that in symmetrical solutions (140 mM K) the channel has a conductance of 246 +/- 4.5 pS (n = 7 patches) and, when Na was added to the bath solution, the permeability ratio (PK/PNa) was 10 and 11 for MG-63 and SaOS-2 cells respectively. In excised patches from MG-63 cells, the channel open probability (Po) is both voltage- (channel opening with depolarization) and Ca-dependent; the presence of Ca shifts the Po vs. voltage curve toward negative membrane potential. Direct modulation of this maxi-K channel via protein kinase A (PKA) is very unlikely since in excised patches the activity of this channel is not sensitive to the addition of 1 mM ATP + 20 U/ml catalytic subunit of PKA. We next evaluated the possibility that PGE2 or PTH stimulated the channel through a rise in intracellular calcium. First, calcium uptake (45Ca2+) by MG-63 cells was stimulated in the presence of PTH and PGE2 an effect inhibited by Nitrendipine (10 microM). Second, whereas PGE2 stimulated the calcium-activated maxi-K channel in 2 mM Ca Ringer in 60% of patches studied, in Ca-free Ringer bath solution, PGE2 did not open any channels (n = 10 patches) nor did cAMP + forskolin (n = 3 patches), although K channels were present under the patch upon excision. In addition, in the presence of 2 mM Ca Ringer and 10 microM Nitrendipine in CAP configuration, PGE2 (n = 5 patches) and cAMP + forskolin (n = 2 patches) failed to open K channels present under the patch. As channel activation by phosphorylation with the catalytic subunit of PKA was not observed, and Nitrendipine addition to the bath or the absence of calcium prevented the opening of this channel, it is concluded that activation of this channel by PTH, PGE2 or dibutyryl cAMP + forskolin is due to an increase in intracellular calcium concentration via Ca influx.

Activation of Na:2Cl:K cotransport by luminal chloride in macula densa cells.

Changes in macula densa intracellular pH (pHi) were used to monitor the direction of flux mediated by the apical Na:2Cl:K cotransporter. At the macula densa, a decrease in luminal [Cl] ([Cl]1) from 60 to 1 mM produced cellular alkalinization secondary to a cascade of events involving a decrease in apical Na:2Cl:K cotransport, a fall in intracellular [Na] ([Na]i) and a stimulation of Na:H exchange. This is supported by the fact that 97% of the change in macula densa pHi with reduction in [Cl]1 was bumetanide-sensitive whereas 92% of this pH change was amiloride-sensitive. We found that, in the presence of 20 mM Na and 5 mM K, a [Cl]1 of 14.3 +/- 2.4 mM (N = 7) produced equilibrium of the apical cotransporter since the pHi obtained under this condition was identical to the pHi found after reducing the net ionic flux to zero with bumetanide. Using this value together with the expected stoichiometry for the bumetanide-sensitive cotransporter, it was estimated that the intracellular [Cl] ([Cl]i) at equilibrium (or in the presence of bumetanide) could be as low as 5 mM. Also, using a Hill number of 2 which is consistent with the present data, the affinity for [Cl]1 was found to be 32.5 mM. Under physiological luminal conditions prevailing at the end of the thick ascending limb (approximately 3.5 mM K, and approximately 25 to 30 mM NaCl), macula densa cells are probably operating close to equilibrium while maintaining a small net reabsorption of Na/K and Cl. Since macula densa cells appear capable of reducing [Cl]i to very low levels, a reabsorptive flux should continue to occur until [NaCl]1 is reduced to 18 mM.

Basic properties and potential regulators of the apical K+ channel in macula densa cells.

These studies examine the properties of an apical potassium (K+) channel in macula densa cells, a specialized group of cells involved in tubuloglomerular feedback signal transmission. To this end, individual glomeruli with thick ascending limbs (TAL) and macula densa cells were dissected from rabbit kidney and the TAL covering macula densa cells was removed. Using patch clamp techniques, we found a high density (up to 54 channels per patch) of K+ channels in the apical membrane of macula densa cells. An inward conductance of 41.1 +/- 4.8 pS was obtained in cell-attached patches (patch pipette, 140 mM K+). In inside-out patches (patch pipette, 140 mM; bath, 5 mM K+), inward currents of 1.1 +/- 0.1 pA (n = 11) were observed at 0 mV and single channel current reversed at a pipette potential of -84 mV giving a permeability ratio (PK/PNa) of over 100. In cell-attached patches, mean channel open probability (N,Po, where N is number of channels in the patch and Po is single channel open probability) was unaffected by bumetanide, but was reduced from 11.3 +/- 2.7 to 1.6 +/- 1.3 (n = 5, p < 0.02) by removal of bath sodium (Na+). Simultaneous removal of bath Na+ and calcium (Ca2+) prevented the Na(+)-induced decrease in N.Po indicating that the effect of Na+ removal on N.Po was probably mediated by stimulation of Ca2+ entry. This interpretation was supported by studies where ionomycin, which directly increases intracellular Ca2+, produced a fall in N.Po from 17.8 +/- 4.0 to 5.9 +/- 4.1 (n = 7, p < 0.02). In inside-out patches, the apical K+ channel was not sensitive to ATP but was directly blocked by 2 mM Ca2+ and by lowering bath pH from 7.4 to 6.8. These studies constitute the first single channel observations on macula densa cells and establish some of the characteristics and regulators of this apical K+ channel. This channel is likely to be involved in macula densa transepithelial Cl- transport and perhaps in the tubuloglomerular feedback signaling process.

Na+ pump inhibition downregulates an ATP-sensitive K+ channel in rabbit proximal convoluted tubule.

In several epithelial and nonepithelial tissues a functional link between the basolateral Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) and a basolateral K+ conductance has been established. However, the nature of this link is unclear. We have previously identified a K+ channel on the basolateral membrane of the proximal convoluted tubule perfused in vitro, the activity of which is increased by stimulation of Na+ transport [J. S. Beck, A. M. Hurst, J.-Y. Lapointe, and R. Laprade. Am. J. Physiol. 264 (Renal Fluid Electrolyte Physiol. 33): F496-F501, 1993]. In the present study we investigate whether basolateral membrane K+ channel activity is tightly coupled to Na(+)-K(+)-ATPase activity. In cell-attached patches (150 mM K+ pipette), following stimulation of channel activity by addition of Na(+)-cotransported solutes to the tubule lumen, mean channel open probability (NPo) was reduced from 0.35 +/- 0.09 to 0.14 +/- 0.06 (n = 7, P < 0.05) by blocking the Na(+)-K(+)-ATPase with 100 microM strophanthidin. In excised patches the channel was reversibly blocked by 2 mM ATP from the cytosolic face of the patch, such that NPo fell to 20.1 +/- 7.0% (n = 5, P < 0.001) of control and recovered to 52.2 +/- 11.2% (n = 5, P < 0.05) after washout of ATP. Diazoxide, a putative opener of ATP-sensitive K+ channels, when added to the bathing solution of an unstimulated tubule (microperfused in the absence of Na(+)-cotransported solutes), increased NPo from 0.046 +/- 0.035 to 0.44 +/- 0.2 (n = 6, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of basolateral K channels in proximal tubule studied during continuous microperfusion.

Potassium channel activity of the basolateral membrane of the collagenase-treated rabbit proximal convoluted tubule (PCT) was studied during continuous luminal microperfusion. In cell-attached patches (high-K pipette) an inwardly rectifying potassium channel was observed with an inward slope conductance of 60.8 +/- 3.3 pS (n = 12) and outward slope conductance of 17.1 +/- 2.7 pS (n = 6). Stimulation of transcellular sodium transport with luminal glucose and alanine increased channel activity [measured as single-channel open probability (NPo)] from 0.19 +/- 0.11 to 0.44 +/- 0.09 (n = 8). This increase in channel activity was not likely to be mediated by either cell depolarization or cell swelling, because channel activity was voltage insensitive over physiological potentials and because the channel was not activated by stretch. However, channel activity was pH sensitive; reducing luminal pH from 7.4 to 6.5 reduced NPo from 0.63 +/- 0.24 to 0.26 +/- 0.16 (n = 5). Our work demonstrates the feasibility of patch clamping the basolateral membrane of microperfused nephron segments. This has allowed us to follow the activity of this potassium channel during an increase in sodium transport and show that its activity does increase during this maneuver. We conclude that: 1) it is possible to patch clamp the basolateral membrane of microperfused nephron segments, and 2) basolateral membrane of the rabbit PCT contains an inwardly rectifying, pH-sensitive potassium channel. The behavior of this channel on stimulation of transcellular sodium transport could explain the macroscopic increase in basolateral potassium conductance observed under similar conditions.

Basolateral membrane potassium channels in rabbit cortical thick ascending limb.

The nature of K exit across the basolateral membrane of rabbit cortical thick ascending limb (CTAL) was investigated using the patch clamp technique. The basolateral membrane was exposed by mild collagenase treatment (0.1 U/ml), and a K-selective inwardly rectifying channel was identified. In cell-attached patches (140 mM K pipette) the inward conductance was 35.0 +/- 1.3 pS (n = 9) compared with an outward conductance of 7.0 +/- 0.9 pS (n = 5), and the current reversed at a pipette potential of -63.5 +/- 3.1 mV (n = 9). The channel is strongly voltage dependent, showing an e-fold increase in open probability per 18-mV depolarization. Barium blocked the channel, reducing both mean open probability and single-channel current amplitude; however, the channel was not Ca sensitive. On excision the channel exhibited rundown, which could not be prevented by 0.1 mM ATP or ATP plus 20 U/ml catalytic subunit of protein kinase A. A few excised patch recordings were possible, which confirmed the presence of a highly K-selective channel with a K-to-Na permeability ratio of 100. In conclusion, 1) it is possible to obtain patch clamp recordings from the rabbit CTAL basolateral membrane using a very mild collagenase treatment, and 2) the exit of K across the basolateral membrane is mediated at least in part by the presence of voltage-sensitive K channels.

Apical membrane potassium channels in frog diluting segment: stimulation by furosemide.

The patch-clamp technique was used to study the activity of apical membrane potassium channels in frog isolated everted diluting segments, and the effect of transport inhibitors on channel activity was assessed. In cell-attached patches with a high-potassium pipette solution and Ringer in the bath the channels show inward rectification (inward conductance, 25.1 pS; outward conductance, 10.5 pS). The channel is selective for potassium over sodium and is voltage dependent with depolarization increasing channel open probability (Po). Furosemide increased channel activity, which resulted exclusively from a significant increase in the number (N) of channels in the patch (control, 2.3 +/- 0.3, n = 8; furosemide, 4.0 +/- 0.4, n = 14) without any significant change in Po. Amiloride blocked the stimulatory effect of furosemide by reducing N to 1.4 +/- 0.6 (n = 6), and amiloride alone also reduced N with no significant change in Po. This suggests that the increase in N in response to furosemide may be secondary to a rise in intracellular pH mediated by activation of the apical Na-H exchanger.

Basolateral ionic permeabilities of macula densa cells.

It has recently been shown that membrane ionic transport pathways of macula densa cells can be measured using conventional microelectrodes. To determine if conductances could be identified at the basolateral membrane of macula densa cells, cortical thick ascending limbs (CTAL) with attached glomeruli were continuously perfused with a 25 mM NaCl bicarbonate-free Ringer solution. Individual basolateral Na+, Cl-, NaCl, and K+ concentrations were altered by isosmotic replacement with N-methyl-D-glucamine and/or cyclamate. Reduction in basolateral [Na+] from 150 to 25 mM hyperpolarized basolateral membrane potential (Vbl) by 9.9 +/- 1.3 mV (n = 10; all data are corrected for changes in liquid junction potential at bath electrode). A decrease in bath [Cl-] from 150 to 25 mM depolarized Vbl by 20 +/- 2.4 mV (n = 13), whereas decreases in bath [NaCl] from 150 to 25 mM depolarized Vbl by 29 +/- 6.8 mV (n = 5). In the presence of 150 mM NaCl bathing solution, a stepwise increase in [K+] from 5 to 15 mM (by replacement of 10 mM NaCl with 10 mM KCl) depolarized Vbl by 3.3 +/- 1.1 mV (n = 8). After correction for individual transepithelial diffusion potentials, Cl conductance averaged 59 +/- 19% of the total basolateral conductance, whereas K+ (23 +/- 8%) and Na+ (17 +/- 10%) contributed significantly less to the overall basolateral conductance. These results indicate that membrane potential of macula densa cells may be very sensitive to alterations in intracellular Cl- activity and suggest that apical transport of NaCl through a furosemide-sensitive Na(+)-K(+)-2Cl- transporter may affect membrane potential in macula densa cells via a change in intracellular Cl- activity.

Acute changes in channel density of amphibian diluting segment.

Intracellular pH is a well-established modulator of the apical membrane potassium conductance of the amphibian diluting segment (early distal tubule). We investigated the modulation of this apical potassium conductance at the single-channel level in everted early distal tubules of the frog. Alkalinization of the bath fluid increased mean channel open probability (NPo) both in the presence and absence of the potassium-hydrogen ionophore nigericin. Reciprocal changes were seen with acidification. Because these effects were observed in cell-attached patches, where the composition of the fluid in the pipette is assumed to remain constant, the observed changes in channel activity were attributed to changes in intracellular pH. Further analysis of the data revealed that the changes in channel activity were produced exclusively by changes in the functional number of channels within the patch (N). We were unable to detect any significant changes in the single-channel open probability (Po). This suggests that the density of channels within a membrane may be far more dynamic than previously assumed.

Stretch-activated channels in single early distal tubule cells of the frog.

1. Single stretch-activated channels have been studied in cell-attached and excised patches from single early distal tubule (diluting segment) cells of Rana temporaria. 2. The channels can be reversibly activated, in both cell-attached and excised patches, by the application of negative pressure to the pipette causing mechanical stretching of the cell membrane. In cell-attached patches, application of 14.8 cmH2O negative pressure to the patch pipette increased reversibly the open probably from 0.11 to 0.87. 3. The channel conductance in the cell-attached configuration with standard Ringer solution in the pipette is 21.3 pS. 4. The channel is non-specific. In excised inside-out patches ion substitution experiments show that the channel does not discriminate between sodium and potassium ions, nor does it appear to select for cations over anions. 5. The channel is voltage sensitive such that depolarizing the cell opens the channel. The open probability at the resting membrane potential, 0.89, was reduced to 0.26 at a hyperpolarizing potential of 100 mV (holding pressure of -20.1 cmH2O or -206 Pa). 6. The sensitivity of the channel to mechanical stretching suggests that the channel may be involved in cell volume regulation.

Apical K+ channels of frog diluting segment: inhibition by acidification.

The apical potassium conductance of the amphibian diluting segment is regulated by the intracellular pH. Alkalinisation of the cytosol, whether directly by bathing the cell in an alkaline medium, or following activation of an apical Na/H exchanger by aldosterone, results in an increase in the K conductance. Early distal tubules were isolated from slices of Frog kidneys and the apical membranes exposed by everting the tubule with the aid of microperfusion pipettes. Single channels in the apical membrane were studied in the cell-attached configuration while the tubules were bathed in Ringer with a pH of either 7.4 (control) or 6.6 (acid). Under control conditions single channel currents were readily seen at the resting membrane potential. Upon acidification of the superfusion solution the open probability of the channels was decreased from 0.76 to 0.15. Thus the reduction in apical conductance is brought about, at least in part, by a reduction in the open probability of the channels upon cellular acidification.