| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Biophysical Journal 65: 29-42 (1993)
© 1993 the Biophysical Society
Department of Physiology and Biophysics, University of Vermont, Colchester 05446.
ABSTRACT
The measurement of single ion channel kinetics is difficult when those channels exhibit subconductance events. When the kinetics are fast, and when the current magnitudes are small, as is the case for Na+, Ca2+, and some K+ channels, these difficulties can lead to serious errors in the estimation of channel kinetics. I present here a method, based on the construction and analysis of mean-variance histograms, that can overcome these problems. A mean-variance histogram is constructed by calculating the mean current and the current variance within a brief "window" (a set of N consecutive data samples) superimposed on the digitized raw channel data. Systematic movement of this window over the data produces large numbers of mean-variance pairs which can be assembled into a two-dimensional histogram. Defined current levels (open, closed, or sublevel) appear in such plots as low variance regions. The total number of events in such low variance regions is estimated by curve fitting and plotted as a function of window width. This function decreases with the same time constants as the original dwell time probability distribution for each of the regions. The method can therefore be used: 1) to present a qualitative summary of the single channel data from which the signal-to-noise ratio, open channel noise, steadiness of the baseline, and number of conductance levels can be quickly determined; 2) to quantify the dwell time distribution in each of the levels exhibited. In this paper I present the analysis of a Na+ channel recording that had a number of complexities. The signal-to-noise ratio was only about 8 for the main open state, open channel noise, and fast flickers to other states were present, as were a substantial number of subconductance states. "Standard" half-amplitude threshold analysis of these data produce open and closed time histograms that were well fitted by the sum of two exponentials, but with apparently erroneous time constants, whereas the mean-variance histogram technique provided a more credible analysis of the open, closed, and subconductance times for the patch. I also show that the method produces accurate results on simulated data in a wide variety of conditions, whereas the half-amplitude method, when applied to complex simulated data shows the same errors as were apparent in the real data. The utility and the limitations of this new method are discussed.
This article has been cited by other articles:
 |
|
 |
|
  M. Poynor, R. Eckert, and S. Nussberger Dynamics of the Preprotein Translocation Channel of the Outer Membrane of Mitochondria Biophys. J., August 1, 2008; 95(3): 1511 - 1522. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 V. Zampini, P. Valli, G. Zucca, and S. Masetto Single-Channel L-Type Ca2+ Currents in Chicken Embryo Semicircular Canal Type I and Type II Hair Cells J Neurophysiol, August 1, 2006; 96(2): 602 - 612. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. M. Kad, S. Kim, D. M. Warshaw, P. VanBuren, and J. E. Baker Single-myosin crossbridge interactions with actin filaments regulated by troponin-tropomyosin PNAS, November 22, 2005; 102(47): 16990 - 16995. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H.-K. Chang, S.-H. Yeh, and R.-C. Shieh A Ring of Negative Charges in the Intracellular Vestibule of Kir2.1 Channel Modulates K+ Permeation Biophys. J., January 1, 2005; 88(1): 243 - 254. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Bahadi, P. V. Farrelly, B. L. Kenna, J. I. Kourie, F. Tagliavini, G. Forloni, and M. Salmona Channels formed with a mutant prion protein PrP(82-146) homologous to a 7-kDa fragment in diseased brain of GSS patients Am J Physiol Cell Physiol, October 1, 2003; 285(4): C862 - C872. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Bahadi, P. V. Farrelly, B. L. Kenna, C. C. Curtain, C. L. Masters, R. Cappai, K. J. Barnham, and J. I. Kourie Cu2+-induced modification of the kinetics of A{beta}(1-42) channels Am J Physiol Cell Physiol, October 1, 2003; 285(4): C873 - C880. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. M. Kad, A. S. Rovner, P. M. Fagnant, P. B. Joel, G. G. Kennedy, J. B. Patlak, D. M. Warshaw, and K. M. Trybus A mutant heterodimeric myosin with one inactive head generates maximal displacement J. Cell Biol., August 4, 2003; 162(3): 481 - 488. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. E. Baker, C. Brosseau, P. Fagnant, and D. M. Warshaw The Unique Properties of Tonic Smooth Muscle Emerge from Intrinsic as Well as Intermolecular Behaviors of Myosin Molecules J. Biol. Chem., August 1, 2003; 278(31): 28533 - 28539. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. P. Littlefield, D. M. Swank, B. M. Sanchez, A. F. Knowles, D. M. Warshaw, and S. I. Bernstein The converter domain modulates kinetic properties of Drosophila myosin Am J Physiol Cell Physiol, April 1, 2003; 284(4): C1031 - C1038. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. J. Thompson, M. H. Nordeen, K. E. Howell, and J. H. Caldwell A Large-Conductance Anion Channel of the Golgi Complex Biophys. J., July 1, 2002; 83(1): 278 - 289. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. R. Alpert, L. A. Mulieri, and D. Warshaw The failing human heart Cardiovasc Res, April 1, 2002; 54(1): 1 - 10. [Full Text] [PDF]
|
|
|
|
|
|
J. R. Moore, E. B. Krementsova, K. M. Trybus, and D. M. Warshaw Myosin V exhibits a high duty cycle and large unitary displacement J. Cell Biol., November 12, 2001; 155(4): 625 - 636. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. K. Lee and K. S. Elmslie Reluctant Gating of Single N-Type Calcium Channels during Neurotransmitter-Induced Inhibition in Bullfrog Sympathetic Neurons J. Neurosci., May 1, 2000; 20(9): 3115 - 3128. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. I. Kourie Calcium dependence of C-type natriuretic peptide-formed fast K+ channel Am J Physiol Cell Physiol, July 1, 1999; 277(1): C43 - C50. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. J. Tyska, D. E. Dupuis, W. H. Guilford, J. B. Patlak, G. S. Waller, K. M. Trybus, D. M. Warshaw, and S. Lowey Two heads of myosin are better than one for generating force and motion PNAS, April 13, 1999; 96(8): 4402 - 4407. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. A. Cleland and A. I. Selverston Inhibitory Glutamate Receptor Channels in Cultured Lobster Stomatogastric Neurons J Neurophysiol, June 1, 1998; 79(6): 3189 - 3196. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. S. Elmslie Identification of the Single Channels that Underlie the N-Type and L-Type Calcium Currents in Bullfrog Sympathetic Neurons J. Neurosci., April 15, 1997; 17(8): 2658 - 2668. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Yamashita, M. J. Tyska, D. M. Warshaw, S. Lowey, and K. M. Trybus Functional Consequences of Mutations in the Smooth Muscle Myosin Heavy Chain at Sites Implicated in Familial Hypertrophic Cardiomyopathy J. Biol. Chem., September 1, 2000; 275(36): 28045 - 28052. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. M. Warshaw, W. H. Guilford, Y. Freyzon, E. Krementsova, K. A. Palmiter, M. J. Tyska, J. E. Baker, and K. M. Trybus The Light Chain Binding Domain of Expressed Smooth Muscle Heavy Meromyosin Acts as a Mechanical Lever J. Biol. Chem., November 17, 2000; 275(47): 37167 - 37172. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. K. Baumann and M. E. Martenson Extracellular Protons Both Increase the Activity and Reduce the Conductance of Capsaicin- Gated Channels J. Neurosci., June 1, 2000; 20(11): RC80 - RC80. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
