A calcium-activated chloride channel in sarcoplasmic reticulum
vesicles from rabbit skeletal muscle.
Kourie, Joseph I., Derek R. Laver, Gerard P. Ahern, and Angela F.
Dulhunty.
Muscle Research Group, John Curtin School of Medical Research, ANU,
PO Box 334, Canberra City, ACT, 2601, AUSTRALIA
APStracts 3:0012C, 1996.
A calcium-activated chloride channel is described in sarcoplasmic
reticulum (SR) enriched vesicles of skeletal muscle incorporated into
lipid bilayers. Small chloride (SCl) channels (n = 20) were rapidly
and reversibly activated when cis (cytoplasmic) [Ca2+] was increased
above 10-7?M, with trans (luminal) [Ca2+] at either 10-3?M or 10-7?M.
The open probability (Po) of single channels increased from zero when
cis [Ca2+] was 10-7?M, to 0.61?+/- 0.12 when [Ca2+] was 10-4?M. High
and low conductance levels in single channel activity were activated
at different cis Ca2+ concentrations. Channel openings to the maximum
conductance, 65?-?75?pS (250/50?mM Cl-, cis/trans), were active when
cis [Ca2+] was increased above 5?x?10-6?M. In contrast to the maximum
conductance, channel openings to submaximal levels between 5 and
40?pS were activated at a lower cis [Ca2+] and dominated channel
activity between 5?x?10-7?M and 5?x?10-6?M. Activation of SCl
channels was Ca2+-specific and not reproduced by cytoplasmic Mg2+
concentrations of 10-3?M. We suggest that the SCl channel arises in
the SR membrane. The Ca2+-dependence of this channel implies that it
is active at Ca2+ concentrations achieved during muscle contraction.
Received 15 September 1995; accepted in final form 21 December
1995.
APS Manuscript Number C556-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96