|
|
|
|
|
|
|
||
The Journal of General Physiology, Vol 99, 841-862, Copyright © 1992 by The Rockefeller University Press
ARTICLES |
F Markwardt and G Isenberg
Department of Physiology, University of Cologne, Germany.
Currents through maxi K+ channels were recorded in inside-out macro- patches. Using a liquid filament switch (Franke, C., H. Hatt, and J. Dudel. 1987. Neurosci, Lett. 77:199-204) the Ca2+ concentration at the tip of the patch electrode ([Ca2+]i) was changed in less than 1 ms. Elevation of [Ca2+]i from less than 10 nM to 3, 6, 20, 50, 320, or 1,000 microM activated several maxi K+ channels in the patch, whereas return to less than 10 nM deactivated them. The time course of Ca(2+)- dependent activation and deactivation was evaluated from the mean of 10- 50 sweeps. The mean currents started a approximately 10-ms delay that was attributed to diffusion of Ca2+ from the tip to the K+ channel protein. The activation and deactivation time courses were fitted with the third power of exponential terms. The rate of activation increased with higher [Ca2+]i and with more positive potentials. The rate of deactivation was independent of preceding [Ca2+]i and was reduced at more positive potentials. The rate of deactivation was measured at five temperatures between 16 and 37 degrees C; fitting the results with the Arrhenius equation yielded an energy barrier of 16 kcal/mol for the Ca2+ dissociation at 0 mV. After 200 ms, the time-dependent processes were in a steady state, i.e., there was no sign of inactivation. In the steady state (200 ms), the dependence of channel openness, N.P(o), on [Ca2+]i yielded a Hill coefficient of approximately 3. The apparent dissociation constant, KD, decreased from 13 microM at -50 mV to 0.5 microM at +70 mV. The dependence of N.P(o) on voltage followed a Boltzmann distribution with a maximal P(o) of 0.8 and a slope factor of approximately 39 mV. The results were summarized by a model describing Ca2+- and voltage-dependent activation and deactivation, as well as steady-state open probability by the binding of Ca2+ to three equal and independent sites within the electrical field of the membrane at an electrical distance of 0.31 from the cytoplasmic side.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  T. Riedel, I. Lozinsky, G. Schmalzing, and F. Markwardt Kinetics of P2X7 Receptor-Operated Single Channels Currents Biophys. J., April 1, 2007; 92(7): 2377 - 2391. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. Nache, J. Kusch, V. Hagen, and K. Benndorf Gating of Cyclic Nucleotide-Gated (CNGA1) Channels by cGMP Jumps and Depolarizing Voltage Steps Biophys. J., May 1, 2006; 90(9): 3146 - 3154. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. M. Herrera, T. J. Heppner, and M. T. Nelson Voltage dependence of the coupling of Ca2+ sparks to BKCa channels in urinary bladder smooth muscle Am J Physiol Cell Physiol, March 1, 2001; 280(3): C481 - C490. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Guia, X. Wan, M. Courtemanche, and N. Leblanc Local Ca2+ Entry Through L-Type Ca2+ Channels Activates Ca2+-Dependent K+ Channels in Rabbit Coronary Myocytes Circ. Res., May 14, 1999; 84(9): 1032 - 1042. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. KURIYAMA, K. KITAMURA, T. ITOH, and R. INOUE Physiological Features of Visceral Smooth Muscle Cells, With Special Reference to Receptors and Ion Channels Physiol Rev, July 1, 1998; 78(3): 811 - 920. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. A. Sullivan, M. H. Holmqvist, and I. B. Levitan Characterization of Gating and Peptide Block of mSlo, a Cloned Calcium-Dependent Potassium Channel J Neurophysiol, December 1, 1997; 78(6): 2937 - 2950. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. J. DiChiara and P. H. Reinhart Redox Modulation of hslo Ca2+-Activated K+ Channels J. Neurosci., July 1, 1997; 17(13): 4942 - 4955. [Abstract] [Full Text] [PDF]
|
|
|
|
