scholarly journals Characterization of OpdH, a Pseudomonas aeruginosa Porin Involved in the Uptake of Tricarboxylates

2006 ◽  
Vol 189 (3) ◽  
pp. 929-939 ◽  
Author(s):  
Sandeep Tamber ◽  
Elke Maier ◽  
Roland Benz ◽  
Robert E. W. Hancock
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Single Channel ◽  
Regulatory System ◽  
Growth Conditions ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Specific Expression ◽  
Large Channel ◽  
Specific Uptake

ABSTRACT The Pseudomonas aeruginosa outer membrane is intrinsically impermeable to many classes of antibiotics, due in part to its relative lack of general uptake pathways. Instead, this organism relies on a large number of substrate-specific uptake porins. Included in this group are the 19 members of the OprD family, which are involved in the uptake of a diverse array of metabolites. One of these porins, OpdH, has been implicated in the uptake of cis-aconitate. Here we demonstrate that this porin may also enable P. aeruginosa to take up other tricarboxylates. Isocitrate and citrate strongly and specifically induced the opdH gene via a mechanism involving derepression by the putative two-component regulatory system PA0756-PA0757. Planar bilayer analysis of purified OpdH demonstrated that it was a channel-forming protein with a large single-channel conductance (230 pS in 1 M KCl; 10-fold higher than that of OprD); however, we were unable to demonstrate the presence of a tricarboxylate binding site within the channel. Thus, these data suggest that the requirement for OpdH for efficient growth on tricarboxylates was likely due to the specific expression of this large-channel porin under particular growth conditions.

scholarly journals Functional Characterization of VJ-gating and Single Channel Conductance of Sheep Cx46 and Cx50 Gap Junctions

2020 ◽  
Vol 118 (3) ◽  
pp. 274a
Author(s):  
Benny Yue ◽  
Bassam G. Haddad ◽  
Umair Khan ◽  
Mena Atalla ◽  
Steve L. Reichow ◽  
...  
Keyword(s):  
Gap Junctions ◽  
Single Channel ◽  
Functional Characterization ◽  
Channel Conductance ◽  
Single Channel Conductance

scholarly journals Lack of negative slope in I-V plots for BK channels at positive potentials in the absence of intracellular blockers

2013 ◽  
Vol 141 (4) ◽  
pp. 493-497 ◽  
Author(s):  
Yanyan Geng ◽  
Xiaoyu Wang ◽  
Karl L. Magleby
Keyword(s):  
Single Channel ◽  
Bk Channels ◽  
Negative Slope ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Linear Current ◽  
Joint Application ◽  
Current Voltage ◽  
Α Subunits

Large-conductance, voltage- and Ca2+-activated K+ (BK) channels display near linear current–voltage (I-V) plots for voltages between −100 and +100 mV, with an increasing sublinearity for more positive potentials. As is the case for many types of channels, BK channels are blocked at positive potentials by intracellular Ca2+ and Mg2+. This fast block progressively reduces single-channel conductance with increasing voltage, giving rise to a negative slope in the I-V plots beyond about +120 mV, depending on the concentration of the blockers. In contrast to these observations of pronounced differences in the magnitudes and shapes of I-V plots in the absence and presence of intracellular blockers, Schroeder and Hansen (2007. J. Gen. Physiol. http://dx.doi.org/10.1085/jgp.200709802) have reported identical I-V plots in the absence and presence of blockers for BK channels, with both plots having reduced conductance and negative slopes, as expected for blockers. Schroeder and Hansen included both Ca2+ and Mg2+ in the intracellular solution rather than a single blocker, and they also studied BK channels expressed from α plus β1 subunits, whereas most previous studies used only α subunits. Although it seems unlikely that these experimental differences would account for the differences in findings between previous studies and those of Schroeder and Hansen, we repeated the experiments using BK channels comprised of α plus β1 subunits with joint application of 2.5 mM Ca2+ plus 2.5 mM Mg2+, as Schroeder and Hansen did. In contrast to the findings of Schroeder and Hansen of identical I-V plots, we found marked differences in the single-channel I-V plots in the absence and presence of blockers. Consistent with previous studies, we found near linear I-V plots in the absence of blockers and greatly reduced currents and negative slopes in the presence of blockers. Hence, studies of conductance mechanisms for BK channels should exclude intracellular Ca2+/Mg2+, as they can reduce conductance and induce negative slopes.

ATP-sensitive K(+)-selective channels of inner medullary collecting duct cells

1994 ◽  
Vol 267 (3) ◽  
pp. F489-F496 ◽  
Author(s):  
S. C. Sansom ◽  
T. Mougouris ◽  
S. Ono ◽  
T. D. DuBose
Keyword(s):  
Single Channel ◽  
Collecting Duct ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Inner Medullary Collecting Duct ◽  
Outward Currents ◽  
Inward Currents ◽  
Excised Patches ◽  
Medullary Collecting Duct

The inner medullary collecting duct (IMCD) in vivo has the capacity to either secrete or reabsorb K+. However, a selective K+ conductance has not been described previously in the IMCD. In the present study, the patch-clamp method was used to determine the presence and properties of K(+)-selective channels in the apical membrane of the inner medullary collecting duct cell line, mIMCD-3. Two types of K(+)-selective channels were observed in both cell-attached and excised patches. The most predominant K+ channel, a smaller conductance K+ channel (SK), was present in cell-attached patches with 140 mM KCl (high bath K+) but not with 135 mM NaCl plus 5 mM KCl (low bath K+) in the bathing solution. The single-channel conductance of SK was 36 pS with inward currents and 29 pS with outward currents in symmetrical 140 mM KCl. SK was insensitive to both voltage and Ca2+. However, SK was inhibited significantly by millimolar concentrations of ATP in excised patches. A second K(+)-selective channel [a larger K+ channel (BK)] displayed a single-channel conductance equal to 132 pS with inward currents and 90 pS with outward currents in symmetrical 140 mM KCl solutions. BK was intermittently activated in excised inside-out patches by Mg(2+)-ATP in concentrations from 1 to 5 mM. With complete removal of Mg2+, BK was insensitive to ATP. BK was also insensitive to potential and Ca2+ and was observed in cell-attached patches with 140 mM KCl in the bath solution. Both channels were blocked reversibly by 1 mM Ba2+ from the intracellular surface but not by external Ba2+.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals The Anaerobic Regulatory Network Required for Pseudomonas aeruginosa Nitrate Respiration

2007 ◽  
Vol 189 (11) ◽  
pp. 4310-4314 ◽  
Author(s):  
Kerstin Schreiber ◽  
Robert Krieger ◽  
Beatrice Benkert ◽  
Martin Eschbach ◽  
Hiroyuki Arai ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Dna Bending ◽  
Regulatory Gene ◽  
Regulatory System ◽  
Growth Conditions ◽  
Anaerobic Growth ◽  
Nitrate Respiration ◽  
Genetic Response ◽  
Anaerobic Conditions ◽  
Regulatory Model

ABSTRACT In Pseudomonas aeruginosa, the narK 1 K 2 GHJI operon encodes two nitrate/nitrite transporters and the dissimilatory nitrate reductase. The narK 1 promoter is anaerobically induced in the presence of nitrate by the dual activity of the oxygen regulator Anr and the N-oxide regulator Dnr in cooperation with the nitrate-responsive two-component regulatory system NarXL. The DNA bending protein IHF is essential for this process. Similarly, narXL gene transcription is enhanced under anaerobic conditions by Anr and Dnr. Furthermore, Anr and NarXL induce expression of the N-oxide regulator gene dnr. Finally, NarXL in cooperation with Dnr is required for anaerobic nitrite reductase regulatory gene nirQ transcription. A cascade regulatory model for the fine-tuned genetic response of P. aeruginosa to anaerobic growth conditions in the presence of nitrate was deduced.

Basolateral potassium channels in renal proximal tubule

1987 ◽  
Vol 253 (3) ◽  
pp. F476-F487 ◽  
Author(s):  
H. Sackin ◽  
L. G. Palmer
Keyword(s):  
Single Channel ◽  
Basolateral Membrane ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
K Channels ◽  
Open Time ◽  
Excised Patches ◽  
The Mean ◽  
Inside Out

Potassium (K+) channels in the basolateral membrane of unperfused Necturus proximal tubules were studied in both cell-attached and excised patches, after removal of the tubule basement membrane by manual dissection without collagenase. Two different K+ channels were identified on the basis of their kinetics: a short open-time K+ channel, with a mean open time less than 1 ms, and a long open-time K+ channel with a mean open time greater than 20 ms. The short open-time channel occurred more frequently than the longer channel, especially in excised patches. For inside-out excised patches with Cl- replaced by gluconate, the current-voltage relation of the short open-time K+ channel was linear over +/- 60 mV, with a K+-Na+ selectivity of 12 +/- 2 (n = 12), as calculated from the reversal potential with oppositely directed Na+ and K+ gradients. With K-Ringer in the patch pipette and Na-Ringer in the bath, the conductance of the short open-time channel was 47 +/- 2 pS (n = 15) for cell-attached patches, 26 +/- 2 pS (n = 15) for patches excised (inside out) into Na-Ringer, and 36 +/- 6 pS (n = 3) for excised patches with K-Ringer on both sides. These different conductances can be partially explained by a dependence of single-channel conductance on the K+ concentration on the interior side of the membrane. In experiments with a constant K+ gradient across excised patches, large changes in Na+ at the interior side of the membrane produced no change in single-channel conductance, arguing against a direct block of the K+ channel by Na+. Finally, the activity of the short open-time channel was voltage gated, where the mean number of open channels decreased as a linear function of basolateral membrane depolarization for potentials between -60 and 0 mV. Depolarization from -60 to -40 mV decreased the mean number of open K+ channels by 28 +/- 8% (n = 6).

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