scholarly journals Lysophosphatidylcholine decreases single channel conductance of inward rectifier K channel in mammalian ventricular myocytes.

1984 ◽  
Vol 34 (2) ◽  
pp. 369-373 ◽  
Author(s):  
Tatsuto KIYOSUE ◽  
Masahiro AOMINE ◽  
Makoto ARITA
Keyword(s):  
Single Channel ◽  
Ventricular Myocytes ◽  
Inward Rectifier ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance

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)

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).

Calcium-dependent inactivation of inwardly rectifying K+ channel in a tumor mast cell line

1992 ◽  
Vol 262 (1) ◽  
pp. C84-C90 ◽  
Author(s):  
M. Mukai ◽  
I. Kyogoku ◽  
M. Kuno
Keyword(s):  
Mast Cell ◽  
Cell Line ◽  
Single Channel ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Whole Cell ◽  
Mast Cell Line ◽  
Inwardly Rectifying ◽  
Inside Out

Antigenic stimulation of rat basophilic leukemia (RBL-2H3) cells, a tumor mast cell line, is associated with an increase in intracellular free Ca2+ concentrations ([Ca2+]i) and membrane polarization. We recorded whole cell and single-channel currents through the inwardly rectifying K+ channel, a major resting conductance of cells, using the patch-clamp technique, and we examined interactions between channel activity and [Ca2+]i. With 10 microM Ca2+ in the pipette, the amplitude of whole cell currents gradually declined within 5 min to 48 +/- 13% of that immediately after rupture of the patch membrane, in the presence of 1 mM ATP which minimized intrinsic rundown. In inside-out patches, activity of the channel was reduced by increasing the concentration of Ca2+ in the internal medium, both in the presence and absence of 1 mM ATP, with no apparent change in single-channel conductance. Time-averaged mean current activity in inside-out patches in the presence of 5 microM Ca2+ was less than 50% of that with Ca2+ of 100 nM or less. These results suggest that a rise in [Ca2+]i leads to a closure of the inwardly rectifying K+ channel. In some inside-out patches, inward currents characterized by burst composed of rapid transitions between open and closed states were observed (flickering currents). Single-channel properties of the flickering currents are similar to the inwardly rectifying K+ channel except for kinetics (single-channel conductance of 24.5 +/- 7.9 pS, inward rectification, and permeability to K+).(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals A Trapped Intracellular Cation Modulates K+ Channel Recovery From Slow Inactivation

2006 ◽  
Vol 128 (2) ◽  
pp. 203-217 ◽  
Author(s):  
Evan C. Ray ◽  
Carol Deutsch
Keyword(s):  
Single Channel ◽  
Rank Order ◽  
Striking Similarity ◽  
K Channel ◽  
Slow Inactivation ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Cellular Excitability ◽  
Activation Gate ◽  
Rate Of Recovery

Upon depolarization, many voltage-gated potassium channels undergo a time-dependent decrease in conductance known as inactivation. Both entry of channels into an inactivated state and recovery from this state govern cellular excitability. In this study, we show that recovery from slow inactivation is regulated by intracellular permeant cations. When inactivated channels are hyperpolarized, closure of the activation gate traps a cation between the activation and inactivation gates. The identity of the trapped cation determines the rate of recovery, and the ability of cations to promote recovery follows the rank order K+ > NH4+ > Rb+ > Cs+ >> Na+, TMA. The striking similarity between this rank order and that for single channel conductance suggests that these two processes share a common feature. We propose that the rate of recovery from slow inactivation is determined by the ability of entrapped cations to move into a binding site in the channel's selectivity filter, and refilling of this site is required for recovery.

Voltage-dependent aminoglycoside blockade of the sarcoplasmic reticulum K+ channel

1986 ◽  
Vol 250 (3) ◽  
pp. C361-C364 ◽  
Author(s):  
Y. Oosawa ◽  
M. Sokabe
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Voltage Dependence ◽  
Single Channel ◽  
Phospholipid Bilayer ◽  
K Channel ◽  
Dependent Manner ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Voltage Dependent ◽  
The Way

Single-channel conductance of the K+ channel from sarcoplasmic reticulum (SR) was reduced by aminoglycoside antibiotics such as neomycin and ribostamycin and also by n-hexylamine from either side of the membrane in a dose- and voltage-dependent manner. K+ channels were incorporated into an artificial phospholipid bilayer. This inhibition follows a single-site titration curve. The voltage dependence of the inhibition is explained by assuming that these drugs bind to the open state of a single channel on one site located approximately 40% of the way through the membrane from the cis side (the side to which SR vesicles are added) when drugs are added to the cis side and bind on another site located approximately 40% of the way through the membrane from the trans side (the opposite side to the cis side) when drugs are added to the trans side.

Activation of ATP-sensitive K channels in heart cells by pinacidil: dependence on ATP

1989 ◽  
Vol 257 (6) ◽  
pp. H2092-H2096 ◽  
Author(s):  
J. P. Arena ◽  
R. S. Kass
Keyword(s):  
Single Channel ◽  
K Channel ◽  
Heart Cells ◽  
Channel Activity ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Atp Binding Site ◽  
Atp Concentration ◽  
Ventricular Cells ◽  
Inside Out

We have investigated the effects of pinacidil on channel activity recorded from inside-out patches of membrane excised from guinea pig ventricular cells. If the cytosolic ATP concentration is greater than 0 but less than 500 microM, pinacidil increases the activity of a channel identified as the ATP-sensitive K channel (IKATP) by its single-channel conductance, its inhibition by ATP, and its sensitivity to glybenclamide. When ATP is greater than 3.0 mM the effects of pinacidil are inhibited. Our experiments show that pinacidil enhances the activity of IKATP in heart cells, but that the action of the drug depends on the ATP concentration of the cytosolic solutions. The results suggest that pinacidil acts indirectly, perhaps at an ATP-binding site that regulates this channel.

Electrical characteristics of inward-rectifying K+ channels in isolated bullfrog oxyntic cells

1991 ◽  
Vol 261 (2) ◽  
pp. G206-G212 ◽  
Author(s):  
H. Mieno ◽  
G. Kajiyama
Keyword(s):  
Single Channel ◽  
Rana Catesbeiana ◽  
Basolateral Membrane ◽  
Inward Rectification ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Open Probability ◽  
K Channels ◽  
Patch Clamp Method

The properties of K+ channels in the isolated oxyntic cells of the bullfrog (Rana catesbeiana) were investigated using the patch-clamp method. Two types of K+ channels on the basolateral membrane were identified on the basis of their electrophysiological and pharmacological properties. The K+ channel most frequently observed has a single-channel conductance of 61.0 +/- 2.9 pS (n = 10) and is activated by an increase in intracellular Ca2+. The other K+ channel has a single-channel conductance of 30.3 +/- 2.7 pS (n = 7), which is activated by adenosine 3',5'-cyclic monophosphate (cAMP). The physiological and pharmacological characteristics common to the two K+ channels are inward-going rectification with a high selectivity for K+ and indirect inhibition by omeprazole. The inward rectification is controlled by intracellular Mg2+ in such a way that the more Mg2+ is applied intracellularly, the more their inward-rectifying property is enhanced. The finding that bethanechol and cAMP increase the open probability of these K+ channels as well as activating the acid secretion indicates that there may be a relationship between these two processes in the oxyntic cells.

Two distinct mechanisms are responsible for single K channel block by internal tetraethylammonium ions

1989 ◽  
Vol 256 (3) ◽  
pp. C683-C687 ◽  
Author(s):  
D. Yamamoto ◽  
N. Suzuki
Keyword(s):  
Single Channel ◽  
K Channel ◽  
Delayed Rectifier ◽  
Channel Block ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Average Current ◽  
Inside Out ◽  
Cytoplasmic Side ◽  
Tetraethylammonium Ions

Tetraethylammonium (TEA) ions blocked the unitary currents through the delayed rectifier potassium channels of Drosophila neurons from the cytoplasmic side of inside-out membrane patches by two distinct mechanisms. First, TEA attenuated the single-channel conductance, probably by producing very rapid block-unblock reactions at the inner mouth of the potassium pore. Second, TEA markedly enhanced the slow inactivation, making the incidence of channel openings highly nonrandom; blank traces with no channel openings during repetitive depolarizations showed a significant tendency to be clustered in the presence of TEA. This second action accounts for almost half of the reduction of average current produced by 10 mM internal TEA.

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