scholarly journals Apical K+ channels in Necturus taste cells. Modulation by intracellular factors and taste stimuli.

1992 ◽  
Vol 99 (4) ◽  
pp. 591-613 ◽  
Author(s):  
T A Cummings ◽  
S C Kinnamon
Keyword(s):  
Apical Membrane ◽  
Basolateral Membrane ◽  
Taste Receptor ◽  
K Channel ◽  
Patch Clamp Recording ◽  
Open Probability ◽  
K Channels ◽  
Voltage Dependent ◽  
Whole Cell Recordings ◽  
Inside Out

The apically restricted, voltage-dependent K+ conductance of Necturus taste receptor cells was studied using cell-attached, inside-out and outside-out configurations of the patch-clamp recording technique. Patches from the apical membrane typically contained many channels with unitary conductances ranging from 30 to 175 pS in symmetrical K+ solutions. Channel density was so high that unitary currents could be resolved only at negative voltages; at positive voltages patch recordings resembled whole-cell recordings. These multi-channel patches had a small but significant resting conductance that was strongly activated by depolarization. Patch current was highly K+ selective, with a PK/PNa ratio of 28. Patches containing single K+ channels were obtained by allowing the apical membrane to redistribute into the basolateral membrane with time. Two types of K+ channels were observed in isolation. Ca(2+)-dependent channels of large conductance (135-175 pS) were activated in cell-attached patches by strong depolarization, with a half-activation voltage of approximately -10 mV. An ATP-blocked K+ channel of 100 pS was activated in cell-attached patches by weak depolarization, with a half-activation voltage of approximately -47 mV. All apical K+ channels were blocked by the sour taste stimulus citric acid directly applied to outside-out and perfused cell-attached patches. The bitter stimulus quinine also blocked all channels when applied directly by altering channel gating to reduce the open probability. When quinine was applied extracellularly only to the membrane outside the patch pipette and also to inside-out patches, it produced a flickery block. Thus, sour and bitter taste stimuli appear to block the same apical K+ channels via different mechanisms to produce depolarizing receptor potentials.

Two types of K+ channel in thick ascending limb of rat kidney

1994 ◽  
Vol 267 (4) ◽  
pp. F599-F605 ◽  
Author(s):  
W. H. Wang
Keyword(s):  
Apical Membrane ◽  
Rat Kidney ◽  
Inhibitory Effect ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
K Channels ◽  
Inside Out

We have used the patch-clamp technique to study the apical K+ channels in the thick ascending limb (TAL) of the rat kidney. Two types of K+ channels, a low-conductance and an intermediate-conductance K+ channel, were identified in both cell-attached and inside-out patches. We confirmed the previously reported intermediate-conductance K+ channel (72 pS), which is inhibited by millimolar cell ATP, acidic pH, Ba2+, and quinidine (4). We now report a second K+ channel in apical membrane of the TAL. The slope conductance of this low-conductance K+ channel is 30 pS, and its open probability is 0.80 in cell-attached patches. This channel is not voltage dependent, and application of 2 mM ATP in the bath inhibits channel activity in inside-out patches. In addition, 250 microM glyburide, an ATP-sensitive K+ channel inhibitor, blocks channel activity, whereas the same concentration of glyburide has no inhibitory effect on the 72-pS K+ channel. Channel activity of the 30-pS K+ channel decreases rapidly upon excision of patches (channel run down). Application of 0.1 mM ATP and the catalytic subunit of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase A (PKA) restores channel activity. Furthermore, addition of 0.1 mM 8-(4-chlorophenylthio)-cAMP or 50-100 pM vasopressin in the cell-attached patches increases channel activity. In conclusion, two types of K+ channels are present in the apical membrane of TAL of rat kidney, and PKA plays an important role in modulation of the low-conductance K+ channel activity.

Ba2+, TEA+, and quinine effects on apical membrane K+ conductance and maxi K+ channels in gallbladder epithelium

1990 ◽  
Vol 259 (1) ◽  
pp. C56-C68 ◽  
Author(s):  
Y. Segal ◽  
L. Reuss
Keyword(s):  
Apical Membrane ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
K Channel ◽  
Dependent Manner ◽  
Gallbladder Epithelium ◽  
Concentration Dependent Manner ◽  
K Channels ◽  
Voltage Dependent ◽  
Channel Currents

The apical membrane of Necturus gallbladder epithelium contains a voltage-activated K+ conductance [Ga(V)]. Large-conductance (maxi) K+ channels underlie Ga(V) and account for 17% of the membrane conductance (Ga) under control conditions. We examined the Ba2+, tetraethylammonium (TEA+), and quinine sensitivities of Ga and single maxi K+ channels. Mucosal Ba2+ addition decreased resting Ga in a concentration-dependent manner (65% block at 5 mM) and decreased Ga(V) in a concentration- and voltage-dependent manner. Mucosal TEA+ addition also decreased control Ga (60% reduction at 5 mM). TEA+ block of Ga(V) was more potent and less voltage dependent that Ba2+ block. Maxi K+ channels were blocked by external Ba2+ at millimolar levels and by external TEA+ at submillimolar levels. At 0.3 mM, quinine (mucosal addition) hyperpolarized the cell membranes by 6 mV and reduced the fractional apical membrane resistance by 50%, suggesting activation of an apical membrane K+ conductance. At 1 mM, quinine both activated and blocked K(+)-conductive pathways. Quinine blocked maxi K+ channel currents at submillimolar concentrations. We conclude that 1) Ba2+ and TEA+ block maxi K+ channels and other K+ channels underlying resting Ga; 2) parallels between the Ba2+ and TEA+ sensitivities of Ga(V) and maxi K+ channels support a role for these channels in Ga(V); and 3) quinine has multiple effects on K(+)-conductive pathways in gallbladder epithelium, which are only partially explained by block of apical membrane maxi K+ channels.

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).

Arachidonic acid inhibits K channels in basolateral membrane of the thick ascending limb

2002 ◽  
Vol 283 (3) ◽  
pp. F407-F414 ◽  
Author(s):  
Rui-Min Gu ◽  
Wen-Hui Wang
Keyword(s):  
Arachidonic Acid ◽  
Basolateral Membrane ◽  
Inhibitory Effect ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
K Channels ◽  
Cytochrome P 450

We have used the patch-clamp technique to study the effect of arachidonic acid (AA) on the basolateral K channels in the medullary thick ascending limb (mTAL) of rat kidney. An inwardly rectifying 50-pS K channel was identified in cell-attached and inside-out patches in the basolateral membrane of the mTAL. The channel open probability ( P o) was 0.51 at the spontaneous cell membrane potential and decreased to 0.25 by 30 mV hyperpolarization. The addition of 5 μM AA decreased channel activity, identified as NP o, from 0.58 to 0.08 in cell-attached patches. The effect of AA on the 50-pS K channel was specific because 10 μM cis-11,14,17-eicosatrienoic acid had no significant effect on channel activity. To determine whether the effect of AA was mediated by AA per se or by its metabolites, we examined the effect of AA on channel activity in the presence of indomethacin, an inhibitor of cyclooxygenase, or N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), an inhibitor of cytochrome P-450 monooxygenase. Inhibition of cyclooxygenase increased channel activity from 0.54 to 0.9. However, indomethacin did not abolish the inhibitory effect of AA on the 50-pS K channel. In contrast, inhibition of cytochrome P-450 metabolism not only increased channel activity from 0.49 to 0.83 but also completely abolished the effect of AA. Moreover, addition of DDMS can reverse the inhibitory effect of AA on channel activity. The notion that the effect of AA was mediated by cytochrome P-450-dependent metabolites of AA is also supported by the observation that addition of 100 nM of 20-hydroxyeicosatetraenoic acid, a main metabolite of AA in the mTAL, can mimic the effect of AA. We conclude that AA inhibits the 50-pS K channel in the basolateral membrane of the mTAL and that the effect of AA is mainly mediated by cytochrome P-450-dependent metabolites of AA.

Two types of voltage-dependent potassium channels in outer hair cells from the guinea pig cochlea

1999 ◽  
Vol 277 (5) ◽  
pp. C913-C925 ◽  
Author(s):  
Thierry van den Abbeele ◽  
Jacques Teulon ◽  
Patrice Tran Ba Huy
Keyword(s):  
Guinea Pig ◽  
Hair Cells ◽  
Basolateral Membrane ◽  
Outer Hair Cells ◽  
Catalytic Subunit ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Guinea Pig Cochlea ◽  
Voltage Dependent ◽  
Inside Out

Cell-attached and cell-free configurations of the patch-clamp technique were used to investigate the conductive properties and regulation of the major K+channels in the basolateral membrane of outer hair cells freshly isolated from the guinea pig cochlea. There were two major voltage-dependent K+ channels. A Ca2+-activated K+ channel with a high conductance (220 pS, P K/ P Na= 8) was found in almost 20% of the patches. The inside-out activity of the channel was increased by depolarizations above 0 mV and increasing the intracellular Ca2+concentration. External ATP or adenosine did not alter the cell-attached activity of the channel. The open probability of the excised channel remained stable for several minutes without rundown and was not altered by the catalytic subunit of protein kinase A (PKA) applied internally. The most frequent K+ channel had a low conductance and a small outward rectification in symmetrical K+ conditions (10 pS for inward currents and 20 pS for outward currents, P K/ P Na= 28). It was found significantly more frequently in cell-attached and inside-out patches when the pipette contained 100 μM acetylcholine. It was not sensitive to internal Ca2+, was inhibited by 4-aminopyridine, was activated by depolarization above −30 mV, and exhibited a rundown after excision. It also had a slow inactivation on ensemble-averaged sweeps in response to depolarizing pulses. The cell-attached activity of the channel was increased when adenosine was superfused outside the pipette. This effect also occurred with permeant analogs of cAMP and internally applied catalytic subunit of PKA. Both channels could control the cell membrane voltage of outer hair cells.

scholarly journals Potassium channel types in arterial chemoreceptor cells and their selective modulation by oxygen.

1992 ◽  
Vol 100 (3) ◽  
pp. 401-426 ◽  
Author(s):  
M D Ganfornina ◽  
J López-Barneo
Keyword(s):  
Time Course ◽  
Single Channel ◽  
K Channel ◽  
Open Probability ◽  
K Channels ◽  
Glomus Cells ◽  
Control Value ◽  
Voltage Dependent ◽  
K Current ◽  
Chemoreceptor Cells

Single K+ channel currents were recorded in excised membrane patches from dispersed chemoreceptor cells of the rabbit carotid body under conditions that abolish current flow through Na+ and Ca2+ channels. We have found three classes of voltage-gated K+ channels that differ in their single-channel conductance (gamma), dependence on internal Ca2+ (Ca2+i), and sensitivity to changes in O2 tension (PO2). Ca(2+)-activated K+ channels (KCa channels) with gamma approximately 210 pS in symmetrical K+ solutions were observed when [Ca2+]i was greater than 0.1 microM. Small conductance channels with gamma = 16 pS were not affected by [Ca2+]i and they exhibited slow activation and inactivation time courses. In these two channel types open probability (P(open)) was unaffected when exposed to normoxic (PO2 = 140 mmHg) or hypoxic (PO2 approximately 5-10 mmHg) external solutions. A third channel type (referred to as KO2 channel), having an intermediate gamma(approximately 40 pS), was the most frequently recorded. KO2 channels are steeply voltage dependent and not affected by [Ca2+]i, they inactivate almost completely in less than 500 ms, and their P(open) reversibly decreases upon exposure to low PO2. The effect of low PO2 is voltage dependent, being more pronounced at moderately depolarized voltages. At 0 mV, for example, P(open) diminishes to approximately 40% of the control value. The time course of ensemble current averages of KO2 channels is remarkably similar to that of the O2-sensitive K+ current. In addition, ensemble average and macroscopic K+ currents are affected similarly by low PO2. These observations strongly suggest that KO2 channels are the main contributors to the macroscopic K+ current of glomus cells. The reversible inhibition of KO2 channel activity by low PO2 does not desensitize and is not related to the presence of F-, ATP, and GTP-gamma-S at the internal face of the membrane. These results indicate that KO2 channels confer upon glomus cells their unique chemoreceptor properties and that the O2-K+ channel interaction occurs either directly or through an O2 sensor intrinsic to the plasma membrane closely associated with the channel molecule.

scholarly journals Gating of maxi K+ channels studied by Ca2+ concentration jumps in excised inside-out multi-channel patches (myocytes from guinea pig urinary bladder).

1992 ◽  
Vol 99 (6) ◽  
pp. 841-862 ◽  
Author(s):  
F Markwardt ◽  
G Isenberg
Keyword(s):  
Steady State ◽  
Time Course ◽  
Boltzmann Distribution ◽  
Hill Coefficient ◽  
K Channel ◽  
Open Probability ◽  
Apparent Dissociation Constant ◽  
K Channels ◽  
The Mean ◽  
Inside Out

Currents through maxi K+ channels were recorded in inside-out macro-patches. Using a liquid filament switch (Franke, C., H. Hatt, and J. Dudel. 1987. Neurosci, Lett. 77:199-204) the Ca2+ concentration at the tip of the patch electrode ([Ca2+]i) was changed in less than 1 ms. Elevation of [Ca2+]i from less than 10 nM to 3, 6, 20, 50, 320, or 1,000 microM activated several maxi K+ channels in the patch, whereas return to less than 10 nM deactivated them. The time course of Ca(2+)-dependent activation and deactivation was evaluated from the mean of 10-50 sweeps. The mean currents started a approximately 10-ms delay that was attributed to diffusion of Ca2+ from the tip to the K+ channel protein. The activation and deactivation time courses were fitted with the third power of exponential terms. The rate of activation increased with higher [Ca2+]i and with more positive potentials. The rate of deactivation was independent of preceding [Ca2+]i and was reduced at more positive potentials. The rate of deactivation was measured at five temperatures between 16 and 37 degrees C; fitting the results with the Arrhenius equation yielded an energy barrier of 16 kcal/mol for the Ca2+ dissociation at 0 mV. After 200 ms, the time-dependent processes were in a steady state, i.e., there was no sign of inactivation. In the steady state (200 ms), the dependence of channel openness, N.P(o), on [Ca2+]i yielded a Hill coefficient of approximately 3. The apparent dissociation constant, KD, decreased from 13 microM at -50 mV to 0.5 microM at +70 mV. The dependence of N.P(o) on voltage followed a Boltzmann distribution with a maximal P(o) of 0.8 and a slope factor of approximately 39 mV. The results were summarized by a model describing Ca2+- and voltage-dependent activation and deactivation, as well as steady-state open probability by the binding of Ca2+ to three equal and independent sites within the electrical field of the membrane at an electrical distance of 0.31 from the cytoplasmic side.

Delayed activation of single mechanosensitive channels in Lymnaea neurons

1994 ◽  
Vol 267 (2) ◽  
pp. C598-C606 ◽  
Author(s):  
D. L. Small ◽  
C. E. Morris
Keyword(s):  
Dynamic Behavior ◽  
Abrupt Onset ◽  
Fundamental Difference ◽  
K Channel ◽  
Mechanosensitive Channels ◽  
Stretch Activation ◽  
Open Probability ◽  
K Channels ◽  
Voltage Dependent ◽  
Lymnaea Neurons

Some stretch-activated (SA) channels challenged with suction jumps exhibit adaptation, a dynamic behavior that can be overlooked because of its mechanical fragility. In previous studies of neuronal SA K channels, we detected no adaptation, but the protocols used were not designed to detect dynamics. Here, we reproduce the adaptation seen by others in Xenopus SA cationic (Cat) channels but show that, with the same protocol, no adaptation occurs with SA K channels. Instead, SA K channels exhibit a different dynamic behavior, delayed activation. Lymnaea SA K channels subjected to pressure jumps responded after a 1- to 4-s delay with a gradual, rather than abrupt, onset of activation. The delay was pressure dependent and was longer for patches from older cultured neurons. Delayed responses were fragile like SA Cat channel adaptation; they disappeared with repeated stimuli. Cytochalasin D decreased the delay and increased the stretch activation of SA K channels. Unlike SA Cat channel adaptation, which occurs only at hyperpolarized potentials, SA K channel delay was not voltage dependent. We note that once SA Cat and SA K channels are "stripped" of their fragile (cytoskeleton-dependent?) dynamics, however, their gating behaviors show little fundamental difference; both are stretch activatable and have a higher open probability at depolarized potentials.

Regulation of small-conductance K+ channel in apical membrane of rat cortical collecting tubule

1990 ◽  
Vol 259 (3) ◽  
pp. F494-F502 ◽  
Author(s):  
W. H. Wang ◽  
A. Schwab ◽  
G. Giebisch
Keyword(s):  
Intracellular Ph ◽  
Apical Membrane ◽  
K Channel ◽  
Selectivity Ratio ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Mean Lifetime ◽  
Collecting Tubules ◽  
Inside Out

We used the patch-clamp technique to study the activity and regulation of single potassium channels in the apical membrane of isolated cortical collecting tubules (CCT) of rat kidney. With 140 mM K+ in the pipette the inward conductance of the channel in cell-attached patches at 37 degrees C was 35 pS (n = 106, NaCl-Ringer or 70 mM KCl and 70 mM NaCl in the bath), and the outward conductance was 15 pS (n = 15, 70 mM NaCl + 70 mM KCl in the bath). Mean open probability (Po) of the channel is voltage independent and 0.96 (n = 106). The channel displayed one open state with a mean lifetime of 18.6 ms and one closed state with a mean lifetime of 0.7 ms (n = 20). Selectivity ratio between K+ and Na+ is 20 (n = 5). High-potassium diet increased channel incidence from control 32% (53 patches with channel from 165 patches) to 64% (53 patches with channels from 83 patches). The channel could be blocked by 1 mM Ba2+ (n = 7, Ba2+ in the pipette); however, 5 mM tetraethylammonium (n = 9, TEA in the pipette) did not block the channel activity. The channel was very sensitive to intracellular pH (n = 6). Changing bath pH facing cytoplasmic side of inside-out patches from 7.4 to 6.9 reversibly reduced Po from 0.9 to 0.1. Addition of 1 mM ATP (n = 7) to bath almost completely inhibited channel activity in inside-out patches. This ATP-induced inhibition was fully reversible and was found to be dependent on the ratio of ATP to ADP, since adding 0.5 mM ADP to bath solution relieved the ATP-induced blockade. Results indicate that intracellular pH, concentration of ATP, and ratio of ATP to ADP are important regulators of potassium channel activity in the apical membrane of rat CCT, and the properties of the channel make it a strong candidate for K+ secretion in this nephron segment.

Basolateral outward rectifier chloride channel in isolated crypts of mouse colon

2000 ◽  
Vol 279 (2) ◽  
pp. G277-G287 ◽  
Author(s):  
Olivier Mignen ◽  
Stéphane Egee ◽  
Martine Liberge ◽  
Brian J. Harvey
Keyword(s):  
Protein Kinase ◽  
Chloride Channels ◽  
Single Channel ◽  
Basolateral Membrane ◽  
Distal Colon ◽  
Open Probability ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Dependent Protein ◽  
Inside Out

Single channel patch-clamp techniques were used to demonstrate the presence of outwardly rectifying chloride channels in the basolateral membrane of crypt cells from mouse distal colon. These channels were rarely observed in the cell-attached mode and, in the inside-out configuration, only became active after a delay and depolarizing voltage steps. Single channel conductance was 23.4 pS between −100 and −40 mV and increased to 90.2 pS between 40 and 100 mV. The channel permeability sequence for anions was: I− > SCN− > Br−> Cl− > NO3 − > F−≫ SO4 2− ≈ gluconate. In inside-out patches, the channel open probability was voltage dependent but insensitive to intracellular Ca2+ concentration. In cell-attached mode, forskolin, histamine, carbachol, A-23187, and activators of protein kinase C all failed to activate the channel, and activity could not be evoked in inside-out patches by exposure to the purified catalytic subunit of cAMP-dependent protein kinase A. The channel was inhibited by 5-nitro-2-(3-phenylpropylamino)benzoate, 9-anthracenecarboxylic acid, and DIDS. Stimulation of G proteins with guanosine 5′- O-(3-thiotriphosphate) decreased the channel open probability and conductance, whereas subsequent addition of guanosine 5′- O-(2-thiodiphosphate) reactivated the channel.

Sign in / Sign up

Export Citation Format

Share Document