Potassium conductance and potassium channels in a primitive insect: The cockroach Periplaneta americana

1993 ◽  
pp. 352-365
Author(s):  
Muriel Amar ◽  
Yves Pichon
Keyword(s):  
Potassium Channels ◽  
Periplaneta Americana ◽  
Potassium Conductance

Two types of K+ channels at the basolateral membrane of proximal tubule: inhibitory effect of taurine

1999 ◽  
Vol 277 (2) ◽  
pp. F290-F297 ◽  
Author(s):  
Jean-François Noulin ◽  
Emmanuelle Brochiero ◽  
Jean-Yves Lapointe ◽  
Raynald Laprade
Keyword(s):  
Potassium Channels ◽  
Time Constant ◽  
Potassium Conductance ◽  
Single Type ◽  
K Channel ◽  
Open Probability ◽  
Open Time ◽  
Voltage Curve ◽  
Current Voltage ◽  
Current Voltage Curve

The cell-attached configuration of the patch-clamp technique was used to investigate the effects of taurine on the basolateral potassium channels of rabbit proximal convoluted tubule. In the absence of taurine, the previously reported ATP-blockable channel, KATP, was observed in 51% of patches. It is characterized by an inwardly rectifying current-voltage curve with an inward slope conductance of 49 ± 5 pS ( n = 15) and an outward slope conductance of 13 ± 6 pS ( n = 15). The KATP channel open probability ( P o) is low, 0.15 ± 0.06 ( n = 15) at a − V p = −100 mV ( V pis the pipette potential), and increases slightly with depolarization. The gating kinetics are characterized by one open time constant (τo = 5.0 ± 1.9 ms, n = 6) and two closed time constants (τC1 = 5.2 ± 1.5 ms, τC2 = 140 ± 40 ms; n = 6). In 34% of patches, a second type of potassium channel, sK, with distinct properties was recorded. Its current-voltage curve is characterized by a sigmoidal shape, with an inward slope conductance of 12 ± 2 pS ( n = 4). Its P o is voltage independent and averages 0.67 ± 0.03 ( n = 4) at − V p = −80 mV. Both its open time and closed time distributions are described by a single time constant (τo = 96 ± 19 ms, τC = 10.5 ± 3.6 ms; n = 4). Extracellular perfusion of 40 mM taurine fails to affect sK channels, whereas KATP channel P o decreases by 75% (from 0.17 ± 0.06 to 0.04 ± 0.02, n = 7, P < 0.05). In conclusion, the absolute basolateral potassium conductance of rabbit proximal tubules is the resulting combination of, at least, two types of potassium channels of roughly equal importance: a high-conductance low-open probability KATP channel and a low-conductance high-open probability sK channel. The previously described decrease in the basolateral absolute potassium conductance by taurine is, however, mediated by a single type of K channel: the ATP-blockable K channel.

Relationship between sodium transport and intracellular ATP in isolated perfused rabbit proximal convoluted tubule

1991 ◽  
Vol 261 (4) ◽  
pp. F634-F639 ◽  
Author(s):  
J. S. Beck ◽  
S. Breton ◽  
H. Mairbaurl ◽  
R. Laprade ◽  
G. Giebisch
Keyword(s):  
Potassium Channels ◽  
Cell Volume ◽  
Intracellular Ph ◽  
Sodium Transport ◽  
Sodium Pump ◽  
Basolateral Membrane ◽  
Potassium Conductance ◽  
Transference Number ◽  
Proximal Convoluted Tubule ◽  
A Cell

The effect of alterations in sodium transport on cell ATP content and pH in the isolated perfused proximal convoluted tubule (PCT) of the rabbit was examined. Stimulating sodium transport by the addition of luminal glucose and alanine decreased cell ATP from 4.44 +/- 0.93 to 2.69 +/- 0.62 mM (n = 4), increased intracellular pH by 0.13 +/- 0.02 (n = 7), and increased cell volume by 0.10 +/- 0.02 nl/mm (n = 4). Blocking the sodium pump with 10(-4) M strophanthidin in tubules in which sodium transport had been stimulated increased cell ATP from 2.04 +/- 0.24 to 2.42 +/- 0.32 mM (n = 6). In parallel experiments the same dose of strophanthidin depolarized the basolateral membrane from -52.6 +/- 1.9 to -6.4 +/- 1.6 mV, depolarized the transepithelial potential from -3.2 +/- 0.3 to -0.1 +/- 0.1 mV, and reduced the basolateral membrane potassium transference number from 0.47 to 0.26 indicating a reduction in basolateral potassium conductance. Since strophanthidin caused a cell alkalinization of 0.15 +/- 0.03, this latter effect cannot be due to changes of intracellular pH. Strophanthidin caused no change in cell volume over the period studied, suggesting that stretch-activated potassium channels are not involved either. Instead, potassium conductance inhibition may be the result of the closure of ATP-sensitive potassium channels. These same channels might thus be partly responsible for the increase in potassium conductance commonly observed during stimulation of sodium transport.

Activation of potassium channels in renal epithelioid cells (MDCK) by extracellular ATP

1989 ◽  
Vol 256 (5) ◽  
pp. C1016-C1021 ◽  
Author(s):  
F. Friedrich ◽  
H. Weiss ◽  
M. Paulmichl ◽  
F. Lang
Keyword(s):  
Potassium Channels ◽  
Single Channel ◽  
Chloride Transport ◽  
Mdck Cells ◽  
Potassium Conductance ◽  
Reversal Potential ◽  
Extracellular Atp ◽  
Extracellular Calcium ◽  
Open Probability ◽  
Inwardly Rectifying

Extracellular ATP has been shown to stimulate transepithelial chloride transport in confluent Madin-Darby canine kidney (MDCK) cell layers and to enhance potassium conductance in subconfluent MDCK cells. The present study has been performed to test for the effect of extracellular ATP on channel activity in patches from subconfluent MDCK cells. Within 8 s, addition of extracellular ATP (10 mumol/l) leads to a sustained, but fully reversible, appearance of potassium-selective channels in cell-attached patches [increase of open probability from 0.03 +/- 0.02 (n = 10) to 0.50 +/- 0.07 (n = 6)]. With the use of pipettes filled with 145 mmol/l KCl, inwardly rectifying property of the channels is disclosed with a single-channel conductance of 65.7 +/- 3.1 pS (n = 9) at zero potential difference between pipette and bath and with a reversal potential of 75.4 +/- 2.0 mV (n = 5; pipette negative vs. reference in the bath). The open probability of the channels is not significantly modified by altering pipette potential from -50 mV, pipette positive, to 50 mV, pipette negative. At extracellular calcium activities of less than 10 nmol/l, ATP leads to a transient activation of channels. In conclusion, extracellular ATP activates inwardly rectifying potassium channels in the cell membrane of subconfluent MDCK cells. A sustained activation of the channels requires the presence of extracellular calcium and is probably mediated by increases in intracellular calcium.

scholarly journals Ionic Species Involved in the Electrical Activity of Single Adult Aminergic Neurones Isolated from the Sixth Abdominal Ganglion of the Cockroach Periplaneta Americana

1989 ◽  
Vol 144 (1) ◽  
pp. 535-549 ◽  
Author(s):  
BRUNO LAPIED ◽  
CLAIRE O. MALÉCOT ◽  
MARCEL PELHATE
Keyword(s):  
Periplaneta Americana ◽  
Potassium Conductance ◽  
Ionic Species ◽  
Resting Potential ◽  
Channel Blockers ◽  
Patch Clamp Technique ◽  
Mgcl2 Concentration ◽  
Dorsal Area ◽  
Ca2 Channels

Adult neurones were obtained by dissociation of the dorsal area of the sixth abdominal (A6) ganglion of the cockroach, and electrical properties were studied with the patch-clamp technique. The neurones showed spontaneous fast action potentials, similar to those recorded with microelectrodes in neurones in situ along the dorsal median line of the A6 ganglion. Synthetic saxitoxin (sSTX) at concentrations of 10 × 10−8 to 1.0×10−7mol l−1 suppressed the action potential (AP) and induced a dose-dependent hyperpolarization of the resting potential, suggesting that two types of sSTX-sensitive Na+ channels are present. The resting potential was dependent on the external concentration of both Na+ and K+, with a similar sensitivity to each, yielding a slope of about 43 mV per 10-fold change in concentration. The delayed outward rectification present under control conditions was reduced by tetraethylammonium chloride (TEA-Cl, 1.0×10−2mol l−1). TEA-Cl or Ca2+-free saline abolished the afterhyperpolarization and increased the overshoot and duration of triggered APs, indicating that a calcium-activated potassium conductance contributes to the falling phase of the AP. At 3.0×10−3mol l−1, the Ca2+ channel blockers MnCl2, CoCl2 and NiCl2 lengthened the AP. A blocker-dependent increase in the overshoot and threshold of the AP and reduction of the afterhyperpolarization were observed, probably reflecting the relative potencies of these ions in blocking Ca2+ channels and thus the Ca2+- activated K+ conductance. Increasing MgCl2 concentration by 3.0 × 10−3mol l−1 had no effect on the AP, indicating that the positive shift of the threshold is due to the blockade of Ca2+ channels present at this potential. The results suggest that these isolated neurones are dorsal unpaired median neurones previously studied in a number of insect species.

Potassium Channel-mediated Hyperpolarization of Mesenteric Vascular Smooth Muscle by Isoflurane 

1999 ◽  
Vol 90 (3) ◽  
pp. 779-788 ◽  
Author(s):  
Naohiro Kokita ◽  
Thomas A. Stekiel ◽  
Mitsuaki Yamazaki ◽  
Zeljko J. Bosnjak ◽  
John P. Kampine ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Potassium Channels ◽  
Vascular Smooth Muscle ◽  
Potassium Channel ◽  
Potassium Conductance ◽  
Inward Rectifier ◽  
Sprague Dawley ◽  
Resistance Arteries ◽  
Inward Rectifier Potassium Channels ◽  
Voltage Dependent

Background A primary source of calcium (Ca2+) necessary for excitation contraction in vascular smooth muscle (VSM) is influx via voltage-dependent Ca2+ channels. Thus, force generation in VSM is coupled closely to resting transmembrane potential, which itself is primarily a function of potassium conductance. Previously, the authors reported that volatile anesthetics hyperpolarize VSM of small mesenteric resistance arteries and capacitance veins. The current study was designed to determine whether isoflurane-mediated hyperpolarization is the result of specific effects on one or more of four types of potassium channels known to exist in VSM. Methods Transmembrane potentials (Em) were recorded from in situ mesenteric capacitance and resistance vessels in Sprague-Dawley rats weighing 250-300 g. In separate experiments, selective inhibitors of each of four types of potassium channels known to exist in VSM were administered in the superfusate of the vessel preparations to assess their effects on isoflurane-mediated hyperpolarization. Results Resting VSM Em ranged from -38 to -43 mV after local sympathetic denervation. Isoflurane produced a significant hyperpolarization (2.7-4.3 mV), whereas each potassium channel inhibitor significantly depolarized (2.8-8.5 mV) the VSM. Both 100 nM iberiotoxin (inhibitor of high conductance calcium-activated potassium channels) and 1 microM glybenclamide (inhibitor of adenosine triphosphatase-sensitive potassium channels) significantly inhibited VSM hyperpolarization induced by 1 MAC (minimum alveolar concentration) levels of inhaled isoflurane (0.1-0.9 mV Em change, which was not significant). In contrast, isoflurane hyperpolarized the VSM significantly despite the presence of 3 mM 4 aminopyridine (inhibitor of voltage-dependent potassium channels) or 10 microM barium chloride (an inhibitor of inward rectifier potassium channels) (3.7-8.2 mV change in VSM Em). Conclusions These results suggest that isoflurane-mediated hyperpolarization (and associated relaxation) of VSM can be attributed in part to an enhanced (or maintained) opening of calcium-activated and adenosine triphosphate-sensitive potassium channels but not voltage-dependent or inward rectifier potassium channels.

Differences between mammalian ventral and dorsal spinal roots in response to blockade of potassium channels during maturation

1985 ◽  
Vol 224 (1236) ◽  
pp. 355-366 ◽  
Keyword(s):  
Potassium Channels ◽  
Action Potential ◽  
Functional Organization ◽  
Potassium Conductance ◽  
Compound Action Potential ◽  
Developmental Differences ◽  
Differential Sensitivity ◽  
Spinal Roots ◽  
The Individual ◽  
Dorsal Spinal

Differences in potassium channel organization between motor and sensory fibres have been described in amphibians but have not previously been examined in mammals. In the present investigation, we studied whole nerve and single axon responses following pharmacological blockade of potassium conductance in rat ventral and dorsal spinal roots during maturation. Our results indicate a differential sensitivity in maturing mammalian motor and sensory fibres which is most apparent in younger roots. Specifically, application of 4-aminopyridine (4-AP) results in a broadening of the compound action potential in ventral roots which is associated with a delayed repolarization of the individual action potential of single fibres. In contrast, blockade of potassium channels in young dorsal roots results in a late negativity in the compound response which is correlated with multispike bursting activity recorded from single sensory fibres. The effects of 4-AP on ventral root fibres diminish earlier in the course of maturation than do the effects of 4-AP in dorsal root fibres. These results demonstrate developmental differences in the functional organization of potassium channels in mammalian motor and sensory axons which may have implications for differences in coding properties between these two classes of axons.

scholarly journals Ethanol Effects on Dopaminergic Ventral Tegmental Area Neurons During Block of Ih: Involvement of Barium-Sensitive Potassium Currents

2008 ◽  
Vol 100 (3) ◽  
pp. 1202-1210 ◽  
Author(s):  
John McDaid ◽  
Maureen A. McElvain ◽  
Mark S. Brodie
Keyword(s):  
Potassium Channels ◽  
Firing Rate ◽  
Ventral Tegmental Area ◽  
Drugs Of Abuse ◽  
Potassium Conductance ◽  
Firing Frequency ◽  
Cationic Current ◽  
Ventral Tegmental ◽  
Ethanol Ethanol ◽  
Rats And Mice

The dopaminergic neurons of the ventral tegmental area (DA VTA neurons) are important for the rewarding and reinforcing properties of drugs of abuse, including ethanol. Ethanol increases the firing frequency of DA VTA neurons from rats and mice. Because of a recent report on block of ethanol excitation in mouse DA VTA neurons with ZD7288, a selective blocker of the hyperpolarization-activated cationic current Ih, we examined the effect of ZD7288 on ethanol excitation in DA VTA neurons from C57Bl/6J and DBA/2J mice and Fisher 344 rats. Ethanol (80 mM) caused only increases in firing rate in mouse DA VTA neurons in the absence of ZD7288, but in the presence of ZD7288 (30 μM), ethanol produced a more transient excitation followed by a decrease of firing. This same biphasic phenomenon was observed in DA VTA neurons from rats in the presence of ZD7288 only at very high ethanol concentrations (160–240 mM) but not at lower pharmacologically relevant concentrations. The longer latency ethanol-induced inhibition was not observed in DA VTA neurons from mice or rats in the presence of barium (100 μM), which blocks G protein–linked potassium channels (GIRKs) and other inwardly rectifying potassium channels. Ethanol may have a direct effect to increase an inhibitory potassium conductance, but this effect of ethanol can only decrease the firing rate if Ih is blocked.

How RCK domains regulate gating of K+ channels

2019 ◽  
Vol 400 (10) ◽  
pp. 1303-1322 ◽  
Author(s):  
Marina Schrecker ◽  
Dorith Wunnicke ◽  
Inga Hänelt
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
Conformational Changes ◽  
Cell Communication ◽  
Potassium Conductance ◽  
Ph Homeostasis ◽  
The Family ◽  
Rck Domain ◽  
Living Organisms ◽  
Electrical Signaling

Abstract Potassium channels play a crucial role in the physiology of all living organisms. They maintain the membrane potential and are involved in electrical signaling, pH homeostasis, cell-cell communication and survival under osmotic stress. Many prokaryotic potassium channels and members of the eukaryotic Slo channels are regulated by tethered cytoplasmic domains or associated soluble proteins, which belong to the family of regulator of potassium conductance (RCK). RCK domains and subunits form octameric rings, which control ion gating. For years, a common regulatory mechanism was suggested: ligand-induced conformational changes in the octameric ring would pull open a gate in the pore via flexible linkers. Consistently, ligand-dependent conformational changes were described for various RCK gating rings. Yet, recent structural and functional data of complete ion channels uncovered that the following signal transduction to the pore domains is divers. The different RCK-regulated ion channels show remarkably heterogeneous mechanisms with neither the connection from the RCK domain to the pore nor the gate being conserved. Some channels even lack the flexible linkers, while in others the gate cannot easily be assigned. In this review we compare available structures of RCK-gated potassium channels, highlight the similarities and differences of channel gating, and delineate existing inconsistencies.

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