scholarly journals The molecular identity of the characean OH− transporter: a candidate related to the SLC4 family of animal pH regulators

PROTOPLASMA ◽  
2021 ◽  
Author(s):  
Bianca N. Quade ◽  
Mark D. Parker ◽  
Marion C. Hoepflinger ◽  
Shaunna Phipps ◽  
Mary A. Bisson ◽  
...  
Keyword(s):  
Inorganic Carbon ◽  
Membrane Conductance ◽  
Resting Potential ◽  
Large Scatter ◽  
Intrinsic Variability ◽  
Molecular Identity ◽  
Ph Banding ◽  
Chara Australis ◽  
Ph Increase ◽  
External Ph

AbstractCharaceae are closely related to the ancient algal ancestors of all land plants. The long characean cells display a pH banding pattern to facilitate inorganic carbon import in the acid zones for photosynthetic efficiency. The excess OH−, generated in the cytoplasm after CO2 is taken into the chloroplasts, is disposed of in the alkaline band. To identify the transporter responsible, we searched the Chara australis transcriptome for homologues of mouse Slc4a11, which functions as OH−/H+ transporter. We found a single Slc4-like sequence CL5060.2 (named CaSLOT). When CaSLOT was expressed in Xenopus oocytes, an increase in membrane conductance and hyperpolarization of resting potential difference (PD) was observed with external pH increase to 9.5. These features recall the behavior of Slc4a11 in oocytes and are consistent with the action of a pH-dependent OH−/H+ conductance. The large scatter in the data might reflect intrinsic variability of CaSLOT transporter activation, inefficient expression in the oocyte due to evolutionary distance between ancient algae and frogs, or absence of putative activating factor present in Chara cytoplasm. CaSLOT homologues were found in chlorophyte and charophyte algae, but surprisingly not in related charophytes Zygnematophyceae or Coleochaetophyceae.

scholarly journals Chloride Fluxes in Isolated Dialyzed Barnacle Muscle Fibers

1972 ◽  
Vol 60 (4) ◽  
pp. 471-497 ◽  
Author(s):  
R. DiPolo
Keyword(s):  
Ph Dependence ◽  
Muscle Fibers ◽  
Membrane Conductance ◽  
Chloride Ions ◽  
Resting Potential ◽  
Constant Field ◽  
Ph Change ◽  
Decreasing Ph ◽  
Barnacle Muscle Fibers ◽  
External Ph

Chloride outflux and influx has been studied in single isolated muscle fibers from the giant barnacle under constant internal composition by means of a dialysis perfusion technique. Membrane potential was continually recorded. The chloride outfluxes and influxes were 143 and 144 pmoles/cm2-sec (mean resting potential: 58 mv, temperature: 22°–24°C) with internal and external chloride concentrations of 30 and 541 mM, respectively. The chloride conductance calculated from tracer measurements using constant field assumptions is about fourfold greater than that calculated from published electrical data. Replacing 97% of the external chloride ions by propionate reduces the chloride efflux by 51%. Nitrate ions applied either to the internal or external surface of the membrane slows the chloride efflux. The external pH dependence of the chloride efflux follows the external pH dependence of the membrane conductance, in the range pH 3.9–4.7, increasing with decreasing pH. In the range pH 5–9, the chloride efflux increased with increasing pH, in a manner similar to that observed in frog muscle fibers. The titration curve for internal pH changes in the range 4.0–7.0 was quantitatively much different from that for external pH change, indicating significant asymmetry in the internal and external pH dependence of the chloride efflux.

scholarly journals The Influence of H+ on the Membrane Potential and Ion Fluxes of Nitella

1968 ◽  
Vol 52 (1) ◽  
pp. 60-87 ◽  
Author(s):  
Hiroshi Kitasato
Keyword(s):  
Membrane Potential ◽  
Membrane Conductance ◽  
Potential Difference ◽  
Potential Change ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Resting Membrane Potential ◽  
Ph Change ◽  
Ph Changes ◽  
External Ph

The resting membrane potential of the Nitella cell is relatively insensitive to [K]o, but behaves like a hydrogen electrode. K+ and Cl- effluxes from the cell were measured continuously, while the membrane potential was changed either by means of a negative feedback circuit or by external pH changes. The experiments indicate that PK and PCl are independent of pH but are a function of membrane potential. Slope ion conductances, GK, GCl, and GNa were calculated from efflux measurements, and their sum was found to be negligible compared to membrane conductance. The possibility that a boundary potential change might be responsible for the membrane potential change was considered but was ruled out by the fact that the peak of the action potential remained at a constant level regardless of pH changes in the external solution. The conductance for H+ was estimated by measuring the membrane current change during an external pH change while the membrane potential was clamped at K+ equilibrium potential. In the range of external pH 5 to 6, H+ chord conductance was substantially equal to the membrane conductance. However, the [H]i measured by various methods was not such as would be predicted from the [H]o and the membrane potential using the Nernst equation. In artificial pond water containing DNP, the resting membrane potential decreased; this suggested that some energy-consuming mechanism maintains the membrane potential at the resting level. It is probable that there is a H+ extrusion mechanism in the Nitella cell, because the potential difference between the resting potential and the H+ equilibrium potential is always maintained notwithstanding a continuous H+ inward current which should result from the potential difference.

Is cyclic guanosine monophosphate the internal 'second messenger' for cholinergic actions on central neurons?

1976 ◽  
Vol 54 (2) ◽  
pp. 172-176 ◽  
Author(s):  
K. Krnjević ◽  
E. Puil ◽  
R. Werman
Keyword(s):  
Time Course ◽  
Membrane Conductance ◽  
Cyclic Guanosine Monophosphate ◽  
Guanosine Monophosphate ◽  
Resting Potential ◽  
Electrical Excitability ◽  
Spinal Motoneurons ◽  
Central Neurons ◽  
Intracellular Cgmp ◽  
Post Synaptic Potential

The most consistent effects produced by intracellular injections of guanosine 3′,5′-cyclic monophosphate (cGMP) (but not 5′-guanosine 5′-monophosphate in spinal motoneurons of cats are a rise in membrane conductance, acceleration in time course of spike potentials, and accentuation of the post-spike hyperpolarization. Associated changes in resting potential are smaller, less constant, and more often in the depolarizing than hyperpolarizing direction. cGMP tends to increase electrical excitability but reduces excitatory post-synaptic potential amplitudes. Most of the effects of intracellular cGMP are quite different from, or indeed opposite to, those of either extra- or intracellular applications of acetylcholine and therefore not consistent with the proposal that cGMP is the internal mediator of muscarinic actions.

scholarly journals Possible mediation of G-proteins in cold-sensory transduction in

1997 ◽  
Vol 200 (6) ◽  
pp. 1025-1030
Author(s):  
Y Nakaoka ◽  
T Tanaka ◽  
T Kuriu ◽  
T Murata
Keyword(s):  
G Proteins ◽  
Membrane Conductance ◽  
Sensory Transduction ◽  
Resting Potential ◽  
Sensory Response ◽  
Current Response ◽  
Protein Activity ◽  
Nucleotide Analogues ◽  
Inward Current ◽  
Aluminium Fluoride

The possible involvement of G-proteins in cold-sensory transduction was examined using voltage-clamped Paramecium multimicronucleatum into which non-hydrolyzable guanosine nucleotide analogues had been applied intracellularly. Guanosine-5'-O-3-thiotriphosphate, guanosine-5'-O-2-thiodiphosphate and aluminium fluoride all reduced the transient inward current in response to cooling, suggesting the possibility that G-proteins mediate cold-sensory transduction. Internal application of a Ca2+ chelator, EGTA, also reduced the current response. In addition to their effect on reducing the cold-sensory response, application of these chemicals modulated both the resting potential and the membrane conductance. Possible correlations between G-protein activity and the regulation of intracellular Ca2+ levels are discussed.

Temperature Effects on Neuromuscular Transmission (Opener Muscle of Crayfish, Astacus Leptodactylus)

1981 ◽  
Vol 94 (1) ◽  
pp. 251-268
Author(s):  
LUDWIG FISCHER ◽  
ERNST FLOREY
Keyword(s):  
Decay Time ◽  
Neuromuscular Transmission ◽  
Membrane Conductance ◽  
Resting Potential ◽  
Muscle Fibres ◽  
Astacus Leptodactylus ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Temperature Range ◽  
Parallel Change

In experiments on the opener muscle of the third walking legs of crayfish (Astacus leptodactylus) it was found that the mechanical tension developed in response to repetitive stimulation of the single motor axon increases over the entire temperature range from 30 down to 0°C. In contrast to this, the tension elicited by depolarizing single muscle fibres decreases with decreasing temperature; the threshold for excitation-contraction coupling is not significantly altered. With decreasing temperature the resting potential decreases (up to 2 mV/°C) but the amplitude and decay time of the e.p.s.p.'s increase. The time constant, λ, of e.p.s.p. decay has a Q10 of less than −2 in the range above 15 °C but reaches a value of −7 between 10 and 0°C. This pattern of temperature dependence is fully accounted for by a parallel change of membrane resistance and its reciprocal, the membrane conductance. The corresponding activation energies computed from λ-values approximate 3 kcal/mol at high temperature and 46 kcal/mol in the low temperature range. The combined effects of a lowered resting potential, an increased amplitude, and especially an increased decay time of e.p.s.p.s result in a drastic enhancement of the depolarization reached during summation of e.p.s.p.s as the temperature is decreased. These effects overcompensate the declining effectiveness of excitation-contraction coupling so that the entire process of neuromuscular transmission becomes more and more effective as the temperature declines. In order to reach the same tension lower frequencies of nerve stimulation are needed at lower temperatures.

Analysis of decreased conductance serotonergic response in Aplysia ink motor neurons

1985 ◽  
Vol 53 (2) ◽  
pp. 590-602 ◽  
Author(s):  
J. P. Walsh ◽  
J. H. Byrne
Keyword(s):  
Cell Body ◽  
Motor Neurons ◽  
Potassium Conductance ◽  
Membrane Conductance ◽  
Resting Potential ◽  
Slow Inward Current ◽  
Equilibrium Potential ◽  
Voltage Sensitivity ◽  
Inward Current ◽  
Bath Application

Micropressure ejection of serotonin (5-hydroxytryptamine, 5-HT) produced excitatory responses in the L14 ink motor neurons of Aplysia that depended on the site of application. Ejection of 5-HT onto the cell body produced a slow response that showed variability in voltage sensitivity between preparations. In contrast, ejection of 5-HT onto the neuropil underneath the cell body produced a response whose amplitude was consistently a linear function of the holding potential, reversing near the predicted potassium equilibrium potential. Subsequent analyses focused on this second response. The neuropil response induced by 5-HT had a linear current-voltage relationship (reversing at ca. -80 mV), was associated with a decrease in input conductance, and was sensitive to changes in the concentration of extracellular K+. Serotonin application in artificial seawater (ASW) containing 30 mM K+ produced a response that reversed close to the altered Nernst potential for K+. The 5-HT response did not appear to be due to secondary activation of interneurons or to depend primarily on extracellular Ca2+, since ejection of 5-HT onto cells bathed in ASW containing 30 mM Co2+ produced responses comparable to, although somewhat attenuated from, those observed in ASW. Serotonin responses similar to those produced in ASW were obtained after perfusing the ganglion with ASW containing Co2+, 4-aminopyridine (4-AP), and tetraethylammonium (TEA). This suggests that the 5-HT-sensitive current is separate from the Ca2+-activated, fast, and delayed rectifying K+ currents. The 5-HT response appeared to be mediated by changes in levels of cAMP. Bath application of the phosphodiesterase inhibitors IBMX (3-isobutyl-1-methylxanthine) or Ro 20-1724, or the adenylate cyclase activator forskolin mimicked the 5-HT response by producing a slow inward current associated with a decrease in membrane conductance. Alteration of cellular cAMP metabolism modulated the response to 5-HT. Exposure of the ganglion to low concentrations of either Ro 20-1724 or forskolin potentiated the 5-HT response. Higher concentrations of these agents largely blocked the response to subsequent 5-HT applications. Bath application of the 8-bromo derivative of either cAMP or cGMP produced a slow inward current associated with a decrease in membrane conductance in cells voltage clamped at the resting potential. Responses to 5-HT were blocked, however, after exposure to 8-bromo-cAMP, but not to 8-bromo-cGMP. These results suggest that 5-HT produces a voltage-independent decrease in a steady-state potassium conductance that may be mediated by cAMP.(ABSTRACT TRUNCATED AT 400 WORDS)

K+-channel blockers do not decrease acetylcholine depolarizations in canine trachealis

1992 ◽  
Vol 70 (1) ◽  
pp. 43-52 ◽  
Author(s):  
E. E. Daniel ◽  
J. Jury ◽  
R. Serio ◽  
L. P. Jager
Keyword(s):  
Chloride Channels ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
Resting Potential ◽  
K Channel ◽  
Channel Blockers ◽  
Membrane Effects ◽  
Sucrose Gap ◽  
Time Courses

Using the double sucrose gap, we have examined the role of K+ channels in the cholinergic depolarizations in response to field stimulation and acetylcholine (Ach) in canine trachealis. Acetylcholine-like depolarization per se decreased electrotonic potentials from hyperpolarizing currents. The net effect of acetylcholine (10−6 M) depolarization on membrane conductance was a small increase after the depolarization was compensated by current clamp. Reversal potentials for acetylcholine depolarization and for the excitatory junction potential (EJP) were determined by extrapolation to be 20–30 mV positive to the resting potential, previously shown to be approximately −55 mV. They were shifted positively by tetraethylammonium ion (TEA) at 20 mM or Ba2+ at 1 mM. TEA or Ba2+ initially depolarized the membrane and increased membrane resistance. Repolarization of the membrane restored any reductions in EJP amplitudes associated with depolarization. After 15 min, the membrane potential partially repolarized, and acetylcholine-induced depolarization and contractions were then increased by TEA. 4-Aminopyridine depolarized the membrane but decreased membrane resistance. Apamin (10−6 M), charybdotoxin (10−7 M), and glybenclamide (10−5 M) each failed to significantly depolarize membranes, increase membrane resistance, or reduce EJP amplitudes or depolarization to 10−6 M Ach. Glybenclamide reduced depolarizations to added acetylcholine slightly. TEA occasionally reduced the EJP markedly, but this was shown to be most likely a prejunctional effect mediated by norepinephrine release. TEA alone among K+-channel blockers slowed the onset and the time courses of the EJP as well as the acetylcholine-induced depolarization. K+-channel closure cannot be a complete explanation of acetylcholine-induced membrane effects on this tissue. Acetylcholine must have increased the conductance of an ion with a reversal potential positive to the resting potential in addition to any effect to close K+ channels.Key words: acetylcholine, tracheal smooth muscle, trachea, chloride channels, sucrose gap, potassium channels, tetraethylammonium, Ba2+.

Effect of external pH on inorganic carbon assimilation in unicellular marine green algae

2000 ◽  
Vol 48 (1) ◽  
pp. 47-54 ◽  
Author(s):  
Laurent Beuf ◽  
Norihide Kurano ◽  
Shigetoh Miyachi
Keyword(s):  
Green Algae ◽  
Inorganic Carbon ◽  
Carbon Assimilation ◽  
External Ph

Cardiac pacemaker potentials at different extra- and intracellular K concentrations

1965 ◽  
Vol 208 (4) ◽  
pp. 770-775 ◽  
Author(s):  
Mario Vassalle
Keyword(s):  
Cardiac Tissue ◽  
Cardiac Pacemaker ◽  
Membrane Conductance ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Minor Effect ◽  
Bathing Solution ◽  
Subthreshold Oscillations ◽  
K Concentration ◽  
A Minor

Transmembrane potentials were recorded from mammalian Purkinje fibers. Adding saccharose to the bathing solution slowed the spontaneous rate, probably as a result of cell shrinkage and an increase in the intracellular K concentration. An opposite result was found with hypotonic medium. In solutions containing 5.4 mm K the fibers were quiescent. Lowering K to 2.7 mm left the membrane resting potential unchanged but decreased the membrane conductance to half. There was only a minor effect of extracellular K on membrane conductance during the plateau of the action potential. Spontaneous firing regularly started when extracellular K was reduced to or below 2.7 mm. This was preceded by subthreshold oscillations which increased in amplitude. A low K conductance associated with a sizeable difference between membrane potential and potassium equilibrium potential seem to be essential for spontaneous activity to occur in cardiac tissue.

Intracellular H+ inhibits a cloned rat kidney outer medulla K+ channel expressed in Xenopus oocytes

1995 ◽  
Vol 268 (5) ◽  
pp. C1173-C1178 ◽  
Author(s):  
T. D. Tsai ◽  
M. E. Shuck ◽  
D. P. Thompson ◽  
M. J. Bienkowski ◽  
K. S. Lee
Keyword(s):  
Xenopus Oocytes ◽  
Rat Kidney ◽  
Ph Sensitivity ◽  
Resting Potential ◽  
K Channel ◽  
K Current ◽  
A Site ◽  
The Relationship ◽  
Inwardly Rectifying ◽  
External Ph

The pH sensitivity of a cloned rat kidney K+ channel, ROMK1, was examined after expression in Xenopus oocytes. Membrane currents and intracellular pH (pHi) were concomitantly monitored by the two-microelectrode voltage-clamp technique and a pH-sensitive microelectrode. Oocytes injected with ROMK1 cRNA developed a hyperpolarized resting potential of -98.7 +/- 0.98 mV and a slightly inwardly rectifying Ba(2+)-sensitive K+ current. Lowering external pH from 7.4 to 6.7 using membrane-permeable acetate buffer reduced measured pHi from 7.2 to 6.6 and reduced the ROMK1 current by 80%. The H+ blockade of ROMK1 currents was voltage independent. The relationship between ROMK1 slope conductance and pHi fitted to a titration curve suggested binding of four H+ to a site with a pK of 6.79. Extracellular acidification from pH 7.4 to 6.0 using membrane-impermeable biphthalate buffer had no effect on the ROMK1 current. The pH sensitivity of the ROMK1 channel is similar to that reported for a small-conductance native kidney K+ channel.

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