|
|
|
|
|
|
|
||
Address correspondence to Tom DeCoursey, Department of Molecular Biophysics and Physiology, Rush Presbyterian St. Luke's Medical Center, 1750 West Harrison, Chicago, IL 60612. Fax: (312) 942-8711; E-mail: tdecours{at}rush.edu
Voltage-gated proton channels were studied under voltage clamp in excised, inside-out patches of human eosinophils, at various pHi with pHo 7.5 or 6.5 pipette solutions. H+ current fluctuations were observed consistently when the membrane was depolarized to voltages that activated H+ current. At pHi 
5.5 the variance increased nonmonotonically with depolarization to a maximum near the midpoint of the H+ conductance-voltage relationship, gH-V, and then decreased, supporting the idea that the noise is generated by H+ channel gating. Power spectral analysis indicated Lorentzian and 1/f components, both related to H+ currents. Unitary H+ current amplitude was estimated from stationary or quasi-stationary variance, 
. We analyze data obtained at various voltages on a linearized plot that provides estimates of both unitary conductance and the number of channels in the patch, without requiring knowledge of open probability. The unitary conductance averaged 38 fS at pHi 6.5, and increased nearly fourfold to 140 fS at pHi 5.5, but was independent of pHo. In contrast, the macroscopic gH was only 1.8-fold larger at pHi 5.5 than at pHi 6.5. The maximum H+ channel open probability during large depolarizations was 0.75 at pHi 6.5 and 0.95 at pHi 5.5. Because the unitary conductance increases at lower pHi more than the macroscopic gH, the number of functional channels must decrease. Single H+ channel currents were too small to record directly at physiological pH, but at pHi 5.5 near Vthreshold (the voltage at which gH turns on), single channel–like current events were observed with amplitudes 7–16 fA.
Key Words: protons • hydrogen ion • ion channels • patch clamp • phagocytes
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  B. Musset, V. V. Cherny, D. Morgan, Y. Okamura, I. S. Ramsey, D. E. Clapham, and T. E. DeCoursey Detailed comparison of expressed and native voltage-gated proton channel currents J. Physiol., May 15, 2008; 586(10): 2477 - 2486. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Sasaki, M. Takagi, and Y. Okamura A Voltage Sensor-Domain Protein Is a Voltage-Gated Proton Channel Science, April 28, 2006; 312(5773): 589 - 592. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Obermeyer and S. D. Tyerman NH4+ Currents across the Peribacteroid Membrane of Soybean. Macroscopic and Microscopic Properties, Inhibition by Mg2+, and Temperature Dependence Indicate a SubpicoSiemens Channel Finely Regulated by Divalent Cations Plant Physiology, October 1, 2005; 139(2): 1015 - 1029. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. L. Bankers-Fulbright, G. M. Kephart, K. R. Bartemes, H. Kita, and S. M. O'Grady Platelet-activating factor stimulates cytoplasmic alkalinization and granule acidification in human eosinophils J. Cell Sci., November 15, 2004; 117(24): 5749 - 5757. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. L. Petheo, A. Maturana, A. Spat, and N. Demaurex Interactions between Electron and Proton Currents in Excised Patches from Human Eosinophils J. Gen. Physiol., November 24, 2003; 122(6): 713 - 726. [Abstract] [Full Text] [PDF]
|
|
|
|
