A calcium-activated chloride channel in sarcoplasmic reticulum vesicles from rabbit skeletal muscle.
A Ca(2+)-activated Cl- 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) or 10(-7) M. The open probability 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+]. 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) 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+] achieved during muscle contraction.
Kourie
J I
JI
John Curtin School of Medical Research, Australian National University, Canberra City, Australia.
Laver
D R
DR
Ahern
G P
GP
Dulhunty
A F
AF
D000818:Animals; D000838:Anions / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D003593:Cytoplasm / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004553:Electric Conductivity; D007202:Indicators and Reagents / Q000494:pharmacology; D015640:Ion Channel Gating; D008274:Magnesium / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000378:metabolism*; D009994:Osmolar Concentration; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D000838:Anions; D018118:Chloride Channels; D007202:Indicators and Reagents; D004533:Egtazic Acid; D008274:Magnesium; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium