Limits...
An external sodium ion binding site controls allosteric gating in TRPV1 channels.

Jara-Oseguera A, Bae C, Swartz KJ - Elife (2016)

Bottom Line: Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation.The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium.Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli.

View Article: PubMed Central - PubMed

Affiliation: Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States.

ABSTRACT
TRPV1 channels in sensory neurons are integrators of painful stimuli and heat, yet how they integrate diverse stimuli and sense temperature remains elusive. Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation. In studying the underlying mechanism, we find that the temperature sensors in TRPV1 activate in two steps to favor opening, and that the binding of sodium to an extracellular site exerts allosteric control over temperature-sensor activation and opening of the pore. The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium. Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli.

No MeSH data available.


Related in: MedlinePlus

Theoretical I-V relations in the presence and absence of external Na+ obtained with the Goldman-Hodgkin-Katz current equation.Superposition of the I-V relations obtained from voltage ramps (Figure 1C) and theoretical I-V curves calculated using the Goldman-Hodgkin-Katz current equation (red curves) with a permeability of TRPV1 for Na+ ions that is 20-fold larger than that for NMDG+. Theoretical I-V relations were calculated with the following equation: where I(V) is the current as a function of voltage (V), N is the number of channels, Po,minis the minimal open probability at V << 0, Po,max is the maximal open probability at V >> 0, z is the gating charge of the channel, V1/2 is the voltage of half-maximal channel activation, F is Faraday’s constant, R is the gas constant, T is the temperature, PX1 is the permeability of the intracellular cation (i.e. Na+), zX1 and zX2 are the charges of the intracellular and extracellular cations, respectively, [X1]iand [X2]o are the molar concentrations of the intracellular (Na+) and extracellular (Na+ or NMDG+) cations, respectively, and f is the permeability ratio for cations 1 and 2 (PX2/PX1). At saturating capsaicin, the parameters used were: Po,min = 0.05; Po,max = 0.9; z = 0.31 e0; V1/2 = 71 mV and f = 1 for 130 Nao or 0.05 for 130 NMDGo. For 130 NMDGo the parameters were: Po,min = 0; Po,max = 0.30; z = 0.72 e0; V1/2 = 99 mV and f = 0.05. A permeability for Na+ of 2.04721 x 10–19 m/s was used.DOI:http://dx.doi.org/10.7554/eLife.13356.007
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4764576&req=5

fig1s4: Theoretical I-V relations in the presence and absence of external Na+ obtained with the Goldman-Hodgkin-Katz current equation.Superposition of the I-V relations obtained from voltage ramps (Figure 1C) and theoretical I-V curves calculated using the Goldman-Hodgkin-Katz current equation (red curves) with a permeability of TRPV1 for Na+ ions that is 20-fold larger than that for NMDG+. Theoretical I-V relations were calculated with the following equation: where I(V) is the current as a function of voltage (V), N is the number of channels, Po,minis the minimal open probability at V << 0, Po,max is the maximal open probability at V >> 0, z is the gating charge of the channel, V1/2 is the voltage of half-maximal channel activation, F is Faraday’s constant, R is the gas constant, T is the temperature, PX1 is the permeability of the intracellular cation (i.e. Na+), zX1 and zX2 are the charges of the intracellular and extracellular cations, respectively, [X1]iand [X2]o are the molar concentrations of the intracellular (Na+) and extracellular (Na+ or NMDG+) cations, respectively, and f is the permeability ratio for cations 1 and 2 (PX2/PX1). At saturating capsaicin, the parameters used were: Po,min = 0.05; Po,max = 0.9; z = 0.31 e0; V1/2 = 71 mV and f = 1 for 130 Nao or 0.05 for 130 NMDGo. For 130 NMDGo the parameters were: Po,min = 0; Po,max = 0.30; z = 0.72 e0; V1/2 = 99 mV and f = 0.05. A permeability for Na+ of 2.04721 x 10–19 m/s was used.DOI:http://dx.doi.org/10.7554/eLife.13356.007

Mentions: To investigate the extent to which the large outward currents in external NMDG+ result from a change in driving force when exchanging external solutions, we obtained current-voltage (I-V) relations using rapid voltage ramps (Figure 1C) or voltage steps in cells exhibiting minimal rundown at room temperature (Figure 1—figure supplement 3). I-V relations for fully activated channels (10 µM capsaicin) in the presence of external Na+ or NMDG+ superimpose at positive voltages (Figure 1C and Figure 1—figure supplement 3), suggesting that the unitary conductance of TRPV1 channels is similar under these conditions. In addition, theoretical I-V relations calculated from the Goldman-Hodgkin-Katz equation predict little change in unitary conductance at positive voltages (Figure 1—figure supplement 4), and we confirmed that exchanging external solutions does not affect the single-channel current amplitude (i) at positive voltages in outside-out patches containing a few channels (Figure 2A). From these results, we conclude that exchanging external Na+ with NMDG+ leads to spontaneous opening of the TRPV1 channel at room temperature.10.7554/eLife.13356.008Figure 2.Extracellular sodium ions are allosteric inhibitors of the TRPV1 channel.


An external sodium ion binding site controls allosteric gating in TRPV1 channels.

Jara-Oseguera A, Bae C, Swartz KJ - Elife (2016)

Theoretical I-V relations in the presence and absence of external Na+ obtained with the Goldman-Hodgkin-Katz current equation.Superposition of the I-V relations obtained from voltage ramps (Figure 1C) and theoretical I-V curves calculated using the Goldman-Hodgkin-Katz current equation (red curves) with a permeability of TRPV1 for Na+ ions that is 20-fold larger than that for NMDG+. Theoretical I-V relations were calculated with the following equation: where I(V) is the current as a function of voltage (V), N is the number of channels, Po,minis the minimal open probability at V << 0, Po,max is the maximal open probability at V >> 0, z is the gating charge of the channel, V1/2 is the voltage of half-maximal channel activation, F is Faraday’s constant, R is the gas constant, T is the temperature, PX1 is the permeability of the intracellular cation (i.e. Na+), zX1 and zX2 are the charges of the intracellular and extracellular cations, respectively, [X1]iand [X2]o are the molar concentrations of the intracellular (Na+) and extracellular (Na+ or NMDG+) cations, respectively, and f is the permeability ratio for cations 1 and 2 (PX2/PX1). At saturating capsaicin, the parameters used were: Po,min = 0.05; Po,max = 0.9; z = 0.31 e0; V1/2 = 71 mV and f = 1 for 130 Nao or 0.05 for 130 NMDGo. For 130 NMDGo the parameters were: Po,min = 0; Po,max = 0.30; z = 0.72 e0; V1/2 = 99 mV and f = 0.05. A permeability for Na+ of 2.04721 x 10–19 m/s was used.DOI:http://dx.doi.org/10.7554/eLife.13356.007
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4764576&req=5

fig1s4: Theoretical I-V relations in the presence and absence of external Na+ obtained with the Goldman-Hodgkin-Katz current equation.Superposition of the I-V relations obtained from voltage ramps (Figure 1C) and theoretical I-V curves calculated using the Goldman-Hodgkin-Katz current equation (red curves) with a permeability of TRPV1 for Na+ ions that is 20-fold larger than that for NMDG+. Theoretical I-V relations were calculated with the following equation: where I(V) is the current as a function of voltage (V), N is the number of channels, Po,minis the minimal open probability at V << 0, Po,max is the maximal open probability at V >> 0, z is the gating charge of the channel, V1/2 is the voltage of half-maximal channel activation, F is Faraday’s constant, R is the gas constant, T is the temperature, PX1 is the permeability of the intracellular cation (i.e. Na+), zX1 and zX2 are the charges of the intracellular and extracellular cations, respectively, [X1]iand [X2]o are the molar concentrations of the intracellular (Na+) and extracellular (Na+ or NMDG+) cations, respectively, and f is the permeability ratio for cations 1 and 2 (PX2/PX1). At saturating capsaicin, the parameters used were: Po,min = 0.05; Po,max = 0.9; z = 0.31 e0; V1/2 = 71 mV and f = 1 for 130 Nao or 0.05 for 130 NMDGo. For 130 NMDGo the parameters were: Po,min = 0; Po,max = 0.30; z = 0.72 e0; V1/2 = 99 mV and f = 0.05. A permeability for Na+ of 2.04721 x 10–19 m/s was used.DOI:http://dx.doi.org/10.7554/eLife.13356.007
Mentions: To investigate the extent to which the large outward currents in external NMDG+ result from a change in driving force when exchanging external solutions, we obtained current-voltage (I-V) relations using rapid voltage ramps (Figure 1C) or voltage steps in cells exhibiting minimal rundown at room temperature (Figure 1—figure supplement 3). I-V relations for fully activated channels (10 µM capsaicin) in the presence of external Na+ or NMDG+ superimpose at positive voltages (Figure 1C and Figure 1—figure supplement 3), suggesting that the unitary conductance of TRPV1 channels is similar under these conditions. In addition, theoretical I-V relations calculated from the Goldman-Hodgkin-Katz equation predict little change in unitary conductance at positive voltages (Figure 1—figure supplement 4), and we confirmed that exchanging external solutions does not affect the single-channel current amplitude (i) at positive voltages in outside-out patches containing a few channels (Figure 2A). From these results, we conclude that exchanging external Na+ with NMDG+ leads to spontaneous opening of the TRPV1 channel at room temperature.10.7554/eLife.13356.008Figure 2.Extracellular sodium ions are allosteric inhibitors of the TRPV1 channel.

Bottom Line: Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation.The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium.Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli.

View Article: PubMed Central - PubMed

Affiliation: Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States.

ABSTRACT
TRPV1 channels in sensory neurons are integrators of painful stimuli and heat, yet how they integrate diverse stimuli and sense temperature remains elusive. Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation. In studying the underlying mechanism, we find that the temperature sensors in TRPV1 activate in two steps to favor opening, and that the binding of sodium to an extracellular site exerts allosteric control over temperature-sensor activation and opening of the pore. The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium. Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli.

No MeSH data available.


Related in: MedlinePlus