ATP‐sensitive K<sup>+</sup>‐channels in the human adult ventricular cardiomyocytes membrane

Babenko, Andrew P.; Samoilov, V. O.; Kazantseva, Svetlana T.; Shevchenko, Yuri L.

doi:10.1016/0014-5793(92)81432-l

Cited by 14 publications

(9 citation statements)

References 12 publications

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“…This hypothesis is consistent with only a small fraction, ϳ1%, of the maximal NP O for K ATP channel population participating in the regulation of insulin secretion from pancreatic ␤-cells (12) or shortening of action potentials of metabolically inhibited ventricular cardiomyocytes (13,14). The hypothesis is consistent with the marginal effect of a decreased submembrane concentration of ATP on K ATP channel activity in situ, e.g.…”

supporting

confidence: 74%

“…Cardiomyocyte Preparation-Human cardiac myocytes were isolated from specimens of myocardium taken from six patients, aged 6 -44 years, during cardiac surgery involving atrial appendage, as described previously for isolation of human ventricular cells (26), except a 2-fold lower concentration of Pronase E was used. Neonatal rat cardiomyocytes were isolated and cultured as described previously (27).…”

Section: Methodsmentioning

confidence: 99%

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A Conserved Inhibitory and Differential Stimulatory Action of Nucleotides on KIR6.0/SUR Complexes Is Essential for Excitation-Metabolism Coupling by KATP Channels

Babenko

Bryan

2001

Journal of Biological Chemistry

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The mechanism by which ubiquitous adenine nucleotide-gated K IR 6.0 4 /SUR 4 channels link membrane excitability with cellular metabolism is controversial. Is a decreased sensitivity to inhibitory ATP required, or is the Mg-ADP/ATP-dependent stimulatory action of the ATPase, sulfonylurea receptor (SUR), on K IR sufficient to elicit a physiologically significant open channel probability? To evaluate the roles of nucleotide inhibition versus stimulation, we compared K IR 6.1-based K NDP channels with K IR 6.2-based K ATP channels and all possible K IR 6.1/6.2 hybrids. Although K NDP channels are thought to be poorly sensitive to inhibitory ATP and to require Mg-nucleotide diphosphates for activity, we demonstrate that, like K ATP , and hybrid channels, they are inhibited with an IC 50(ATP) 100-fold lower than The primary signaling mechanism that attunes the P O to the cellular metabolic status remains controversial. Observations that K ATP channels burst spontaneously in inside-out patches and show reversible inhibition by submillimolar ATP (4 -6) suggested that opening these K IR s in vivo, in the face of millimolar nucleotide, would necessitate a significant decrease in their sensitivity to ATP. The reduction in the ATP sensitivity of isolated K ATP channels upon treatment with numerous substances has been interpreted as evidence for the plasticity of ATP-inhibitory gating in vivo. Following the report (7) that ATP weakly inhibits K IR 6.2-based channels in the absence of SUR (IC 50(ATP) ϭ ϳ0.2 mM versus ϳ5-20 M with SURs; Refs. 8 and 9), K IR -based plasticity of ATP inhibition has been considered a possible cause of the variable activity observed for K ATP channel isoforms in situ.An alternative idea is that SURs, obligatory regulatory subunits of K ATP channels and members of the ABC superfamily (10, 11), act as nucleotide sensors and, in vivo, SURs would exert a Mg-ADP/ATP-dependent stimulatory action sufficient to overcome the saturated inhibitory effect of nucleotides at noncanonical nucleotide binding site(s) on the K IR (1). This hypothesis is consistent with only a small fraction, ϳ1%, of the maximal NP O for K ATP channel population participating in the regulation of insulin secretion from pancreatic ␤-cells (12) or shortening of action potentials of metabolically inhibited ventricular cardiomyocytes (13,14). The hypothesis is consistent with the marginal effect of a decreased submembrane concentration of ATP on K ATP channel activity in situ, e.g. the enhancement of K ATP currents observed when adenylyl cyclases are maximally stimulated, thus reducing ATP without producing stimulatory MgADP, in cardiomyocytes dialyzed with submillimolar ATP, but not in the perforated patch or conventional whole-cell configuration with millimolar [ATP] i (15). The physiologic significance of the Mg-nucleotide-dependent stimulation of K IR 6.2 has been established by the identification of SUR1 mutations that compromise the stimulatory, but not the inhibitory action of Mg-nucleotides on pancreatic ␤-cell K ATP channels (...

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supporting

confidence: 74%

Section: Methodsmentioning

confidence: 99%

A Conserved Inhibitory and Differential Stimulatory Action of Nucleotides on KIR6.0/SUR Complexes Is Essential for Excitation-Metabolism Coupling by KATP Channels

Babenko

Bryan

2001

Journal of Biological Chemistry

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“…In the study of Kakei et al (1985) on cardiac cells, various levels of subconductance states were reported at normal pHi, but their relative rarity precluded detailed analysis. Similar subconductance events were also observed in a recent report on IK,ATP from human ventricular myocytes at pHi 7.2 (Babenko et al, 1992), but again no detailed analysis was done. In the IK,ATP channel of rat skeletal muscle fibers, multiple subconductance levels appeared after adding and withdrawing the channel blocker adenine to the cytoplasmic side of the membrane (Weik, L6nnendonker & Neumcke, 1989).…”

Section: S U B C O N D U C T a N C E S T A T E S Of Ikatp C H A N N supporting

confidence: 80%

Cytoplasmic acidosis induces multiple conductance states in ATP-sensitive potassium channels of cardiac myocytes

et al. 1993

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We studied the effect of cytoplasmic acidosis on the ionic conducting states of ATP-sensitive potassium channels in heart ventricular cells of guinea pigs and rabbits by using a patch-clamp technique with inside-out patch configuration. Under normal conditions (pH 7.4), the channel alternated between a closed state and a main open state in the absence of nucleotides on the cytoplasmic side. As internal pH was reduced below 6.5, the single channel current manifested distinct subconductance levels. The probability of the appearance of these subconductance levels was pH dependent with a greater probability of subconductance states at lower pH. A variance-mean amplitude analysis technique revealed two subconductance levels approximately equally spaced between the main open level and the closed level (63 and 33%). A current-voltage plot of the two subconductance levels and the main level showed that they had similar reversal potentials and rectification properties. An intrinsic flickering gating property characteristic of these ATP-sensitive channels was found unchanged in the 63% subconductance state, suggesting that this subconductance state and the main conductance state share similar ion pore properties (including ion selection and block) and similar gating mechanisms. The appearance of the subconductance states decreased as ionic strength was increased, and the subconductance states were also slightly voltage dependent, suggesting an electrostatic interaction between the protons and the negative surface charge in the vicinity of the binding sites, which may be close to the inner entrance of the ion pore. Proteolytic modification of the channel on the cytoplasmic side with trypsin did not abolish the subconductance levels. External acidosis did not induce subconductance levels. These results suggest that protons bound to the negatively charged group at the inner entrance of the channel ion pore may induce conformational changes, leading to partially reduced conductance states.

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“…3 Rat ventricular cells were prepared as described previously. 29 Clearly striated, single cardiomyocytes with a length-to-width ratioϾ4, shown to have a zerocurrent potential of Ϫ69Ϯ2 mV (measured in 4 cells using the whole-cell configuration under quasi-physiological ionic conditions) were selected for patch-clamp experiments.…”

Section: Isolation Of Cardiomyocytesmentioning

confidence: 99%

“…These channels are abundant in mammalian cardiomyocytes, including adult human ventricular 3 and atrial 4 cells. Cardiac K ATP channels exhibit a rich regulatory phenomenology 5,6 whose underlying structure-function relationships have been difficult to investigate in the absence of a well-defined recombinant channel.…”

mentioning

confidence: 99%

Reconstituted Human Cardiac K _ATP Channels

Babenko

González

Aguilar‐Bryan

et al. 1998

Circulation Research

157

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Abstract-ATP-sensitive potassium (K ATP ) channels in striated myocytes are heteromultimers of K IR 6.2, a weak potassium inward rectifier, plus SUR2A, a low-affinity sulfonylurea receptor. We have cloned human K IR 6.2 (huK IR 6.2) and a huSUR2A that corresponds to the major, full-length splice variant identified by polymerase chain reaction analysis of human cardiac poly A ϩ mRNA. ATP-and glibenclamide-sensitive K ϩ channels were produced when both subunits were coexpressed in COSm6 and Chinese hamster ovary cells lacking endogenous K ATP channels, but not when huSUR2A or huK IR 6.2 were transfected alone. Recombinant channels activated by metabolic inhibition in cell-attached configuration or in inside-out patches with ATP-free internal solution were compared with sarcolemmal K ATP channels in human ventricular cells. The single-channel conductance of Ϸ80 pS measured at Ϫ40 mV in quasi-symmetrical Ϸ150 mmol/L K ϩ solutions, the intraburst kinetics that were dependent on K ϩ driving force, and the weak inward rectification were indistinguishable for both channels. Similar to the native channels, huSUR2A/huK IR 6.2 recombinant channels were inhibited by ATP at quasi-physiological free Mg 2ϩ (Ϸ0.7 mmol/L) or in the absence of Mg 2ϩ , with an apparent IC 50 of Ϸ20 mol/L and a pseudo-Hill coefficient of Ϸ1. They were "refreshed" by MgATP and stimulated by ADP in the presence of Mg 2ϩ when inhibited by ATP. The huSUR2A/huK IR 6.2 channels were stimulated by cromakalim and pinacidil in the presence of ATP and Mg 2ϩ but were insensitive to diazoxide. The results suggest that reconstituted huSUR2A/huK IR 6.2 channels represent K ATP channels in sarcolemma of human cardiomyocytes and are an adequate experimental model with which to examine structure-function relationships, molecular physiology, and pharmacology of these channels from human heart. (Circ Res. 1998;83:1132-1143.)

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ATP‐sensitive K⁺‐channels in the human adult ventricular cardiomyocytes membrane

Cited by 14 publications

References 12 publications

A Conserved Inhibitory and Differential Stimulatory Action of Nucleotides on KIR6.0/SUR Complexes Is Essential for Excitation-Metabolism Coupling by KATP Channels

A Conserved Inhibitory and Differential Stimulatory Action of Nucleotides on KIR6.0/SUR Complexes Is Essential for Excitation-Metabolism Coupling by KATP Channels

Cytoplasmic acidosis induces multiple conductance states in ATP-sensitive potassium channels of cardiac myocytes

Reconstituted Human Cardiac K _ATP Channels

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ATP‐sensitive K+‐channels in the human adult ventricular cardiomyocytes membrane

Cited by 14 publications

References 12 publications

A Conserved Inhibitory and Differential Stimulatory Action of Nucleotides on KIR6.0/SUR Complexes Is Essential for Excitation-Metabolism Coupling by KATP Channels

A Conserved Inhibitory and Differential Stimulatory Action of Nucleotides on KIR6.0/SUR Complexes Is Essential for Excitation-Metabolism Coupling by KATP Channels

Cytoplasmic acidosis induces multiple conductance states in ATP-sensitive potassium channels of cardiac myocytes

Reconstituted Human Cardiac K ATP Channels

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Product

Resources

About

ATP‐sensitive K⁺‐channels in the human adult ventricular cardiomyocytes membrane

Reconstituted Human Cardiac K _ATP Channels