HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 557/1/207    most recent jphysiol.2003.060509v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sun, X.-P. Articles by Grinnell, A. D. Search for Related Content PubMed PubMed Citation Articles by Sun, X.-P. Articles by Grinnell, A. D.

Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA

Single channel properties of Ca²⁺-activated K⁺ (BK or Maxi-K) channels have been investigated in presynaptic membranes in Xenopus motoneurone–muscle cell cultures. The occurrence and density of BK channels increased with maturation/synaptogenesis and was not uniform: highest at the release face of bouton-like synaptic varicosities in contact with muscle cells, and lowest in varicosities that did not contact muscle cells. The Ca²⁺ affinity of the channel (K_d= 7.7 µM at a membrane potential of +20 mV) was lower than those of BK channels that have been characterized in other terminals. Hill coefficients varied between 1.5 and 2.8 at different potentials and open probability increased e-fold per 16 mV change in membrane potential over a range of [Ca²⁺]_i from 1 µM to 1 mM. The maximal activation rate of ensembled single BK channel currents was in the submillisecond range at +20 mV. The activation rate increased 10-fold in response to a [Ca²⁺]_i increase from 1 to 100 µM, but increased only 2-fold with a voltage change from +20 to +130 mV. The fastest activation kinetics of BK channels in cell-attached patches resembled that in inside-out patches with [Ca²⁺]_i of 100 µM or more, suggesting that many BK channels are located very close to calcium channels. Given the low Ca²⁺ affinity and rapid Ca²⁺ binding/unbinding properties, we conclude that BK channels in this preparation are adapted to play an important role in regulation of neurotransmitter release, and they are ideal reporters of local [Ca²⁺] at the inner membrane surface.

(Received 8 January 2004; accepted after revision 25 March 2004; first published online 26 March 2004)
Corresponding author A. D. Grinnell: Department of Physiology, David Geffen School of Medicine at UCLA, Los Angles, CA 90095-1751, USA.  Email: adg{at}ucla.edu

This article has been cited by other articles:

				M. J. Palmer Modulation of Ca2+-activated K+ currents and Ca2+-dependent action potentials by exocytosis in goldfish bipolar cell terminals J. Physiol., May 1, 2006; 572(3): 747 - 762. [Abstract] [Full Text] [PDF]

				L. Hu, H. Yang, J. Shi, and J. Cui Effects of Multiple Metal Binding Sites on Calcium and Magnesium-dependent Activation of BK Channels J. Gen. Physiol., December 27, 2005; 127(1): 35 - 50. [Abstract] [Full Text] [PDF]