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CO2-dependent opening of an inwardly rectifying K+ channel.

Huckstepp RT, Dale N - Pflugers Arch. (2011)

Bottom Line: This reversal potential was shifted by +61 mV following a tenfold increase in extracellular [K(+)] but was insensitive to variations of extracellular [Cl(-)].We propose that this channel is a member of the Kir family.In addition to this K(+) channel, we found that many of the excised patches also contained a conductance carried via a Cl(-)-selective channel.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK.

ABSTRACT
CO(2) chemosensing is a vital function for the maintenance of life that helps to control acid-base balance. Most studies have reported that CO(2) is measured via its proxy, pH. Here we report an inwardly rectifying channel, in outside-out excised patches from HeLa cells that was sensitive to modest changes in PCO(2) under conditions of constant extracellular pH. As PCO(2) increased, the open probability of the channel increased. The single-channel currents had a conductance of 6.7 pS and a reversal potential of -70 mV, which lay between the K(+) and Cl(-) equilibrium potentials. This reversal potential was shifted by +61 mV following a tenfold increase in extracellular [K(+)] but was insensitive to variations of extracellular [Cl(-)]. The single-channel conductance increased with extracellular [K(+)]. We propose that this channel is a member of the Kir family. In addition to this K(+) channel, we found that many of the excised patches also contained a conductance carried via a Cl(-)-selective channel. This CO(2)-sensitive Kir channel may hyperpolarize excitable cells and provides a potential mechanism for CO(2)-dependent inhibition during hypercapnia.

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Increasing PCO2 increases open probability of a small conductance channel. a Continuous record of the effects of different CO2 concentrations on channel gating in outside-out patches from HeLa cells. Note that the effect of changing PCO2 from the control level of 35 mmHg to the levels marked on the black bars on channel gating was rapid. Isolated patch was held at +10 mV. b Expanded traces from a demonstrating the gating of the channels in the patch. Dotted lines represent different levels of channel openings, and multiple openings are only seen at the higher levels of PCO2. c All-points histograms obtained from the data in b and fitted with sums of Gaussian distributions to estimate Po. d Plot of Po vs PCO2 (n = 5 for each point; bars are SEMs). Continuous line is drawn to the Hill equation, Po                                        = 1/(1 + (45/PCO2)2)
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Fig1: Increasing PCO2 increases open probability of a small conductance channel. a Continuous record of the effects of different CO2 concentrations on channel gating in outside-out patches from HeLa cells. Note that the effect of changing PCO2 from the control level of 35 mmHg to the levels marked on the black bars on channel gating was rapid. Isolated patch was held at +10 mV. b Expanded traces from a demonstrating the gating of the channels in the patch. Dotted lines represent different levels of channel openings, and multiple openings are only seen at the higher levels of PCO2. c All-points histograms obtained from the data in b and fitted with sums of Gaussian distributions to estimate Po. d Plot of Po vs PCO2 (n = 5 for each point; bars are SEMs). Continuous line is drawn to the Hill equation, Po  = 1/(1 + (45/PCO2)2)

Mentions: In the course of studying the CO2 sensitivity of connexins [11], we observed a small conductance channel in excised outside-out patches drawn from HeLa cells that exhibited sensitivity to changes in PCO2—the frequency of channel openings rapidly increased as the level of PCO2 increased (Fig. 1a, b). As extracellular pH was kept constant while PCO2 was changed (see “Methods”), the change in channel gating was unlikely to be due to alterations of extracellular pH. Equally changes in pH on the intracellular face of the membrane are also unlikely under this recording configuration as the excised patch has a very small membrane surface area, and it is improbable that CO2 would be able to diffuse through the membrane patch at a sufficient rate to rapidly alter the pH of the patch recording solution and hence channel gating. The CO2-dependent opening of the channel is thus most likely due to the direct effects of CO2 on the channel.Fig. 1


CO2-dependent opening of an inwardly rectifying K+ channel.

Huckstepp RT, Dale N - Pflugers Arch. (2011)

Increasing PCO2 increases open probability of a small conductance channel. a Continuous record of the effects of different CO2 concentrations on channel gating in outside-out patches from HeLa cells. Note that the effect of changing PCO2 from the control level of 35 mmHg to the levels marked on the black bars on channel gating was rapid. Isolated patch was held at +10 mV. b Expanded traces from a demonstrating the gating of the channels in the patch. Dotted lines represent different levels of channel openings, and multiple openings are only seen at the higher levels of PCO2. c All-points histograms obtained from the data in b and fitted with sums of Gaussian distributions to estimate Po. d Plot of Po vs PCO2 (n = 5 for each point; bars are SEMs). Continuous line is drawn to the Hill equation, Po                                        = 1/(1 + (45/PCO2)2)
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3037493&req=5

Fig1: Increasing PCO2 increases open probability of a small conductance channel. a Continuous record of the effects of different CO2 concentrations on channel gating in outside-out patches from HeLa cells. Note that the effect of changing PCO2 from the control level of 35 mmHg to the levels marked on the black bars on channel gating was rapid. Isolated patch was held at +10 mV. b Expanded traces from a demonstrating the gating of the channels in the patch. Dotted lines represent different levels of channel openings, and multiple openings are only seen at the higher levels of PCO2. c All-points histograms obtained from the data in b and fitted with sums of Gaussian distributions to estimate Po. d Plot of Po vs PCO2 (n = 5 for each point; bars are SEMs). Continuous line is drawn to the Hill equation, Po  = 1/(1 + (45/PCO2)2)
Mentions: In the course of studying the CO2 sensitivity of connexins [11], we observed a small conductance channel in excised outside-out patches drawn from HeLa cells that exhibited sensitivity to changes in PCO2—the frequency of channel openings rapidly increased as the level of PCO2 increased (Fig. 1a, b). As extracellular pH was kept constant while PCO2 was changed (see “Methods”), the change in channel gating was unlikely to be due to alterations of extracellular pH. Equally changes in pH on the intracellular face of the membrane are also unlikely under this recording configuration as the excised patch has a very small membrane surface area, and it is improbable that CO2 would be able to diffuse through the membrane patch at a sufficient rate to rapidly alter the pH of the patch recording solution and hence channel gating. The CO2-dependent opening of the channel is thus most likely due to the direct effects of CO2 on the channel.Fig. 1

Bottom Line: This reversal potential was shifted by +61 mV following a tenfold increase in extracellular [K(+)] but was insensitive to variations of extracellular [Cl(-)].We propose that this channel is a member of the Kir family.In addition to this K(+) channel, we found that many of the excised patches also contained a conductance carried via a Cl(-)-selective channel.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK.

ABSTRACT
CO(2) chemosensing is a vital function for the maintenance of life that helps to control acid-base balance. Most studies have reported that CO(2) is measured via its proxy, pH. Here we report an inwardly rectifying channel, in outside-out excised patches from HeLa cells that was sensitive to modest changes in PCO(2) under conditions of constant extracellular pH. As PCO(2) increased, the open probability of the channel increased. The single-channel currents had a conductance of 6.7 pS and a reversal potential of -70 mV, which lay between the K(+) and Cl(-) equilibrium potentials. This reversal potential was shifted by +61 mV following a tenfold increase in extracellular [K(+)] but was insensitive to variations of extracellular [Cl(-)]. The single-channel conductance increased with extracellular [K(+)]. We propose that this channel is a member of the Kir family. In addition to this K(+) channel, we found that many of the excised patches also contained a conductance carried via a Cl(-)-selective channel. This CO(2)-sensitive Kir channel may hyperpolarize excitable cells and provides a potential mechanism for CO(2)-dependent inhibition during hypercapnia.

Show MeSH
Related in: MedlinePlus