ISSN:
1432-1424
Keywords:
Chloride channel
;
Cardiac sarcoplasmic reticulum
;
Planar lipid bilayer
;
Ion selectivity
;
Voltage
;
Block
;
pH
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract We have characterized a voltage-sensitive chloride channel from cardiac sarcoplasmic reticulum (SR) following reconstitution of porcine heart SR into planar lipid bilayers. In 250 mm KCl, the channel had a main conductance level of 130 pS and exhibited two substrates of 61 and 154 pS. The channel was very selective for Cl− over K+ or Na+ ( $$P_{{\text{K}}^{\text{ + }} } /P_{{\text{Cl}}^{\text{ - }} } = 0.012$$ and $$P_{{\text{Na}}^{\text{ + }} } /P_{{\text{Cl}}^{\text{ - }} } \sim 0.040$$ ). It was permeable to several anions and displayed the following sequence of anion permeability: SCN− 〉 I− 〉 NO 3 − ∼ Br− 〉 Cl− 〉 f− 〉 HCOO−. Single-channel conductance saturated with increasing Cl− concentrations (K m= 900 mm and γmax = 488 pS). Channel activity was voltage dependent, with an open probability ranging from ∼1.0 around 0 mV to ∼0.5 at +80 mV. From −20 to +80 mV, channel gating was time-independent. However, at voltages below −40 mV the channel entered a long-lasting closed state. Mean open times varied with voltage, from ∼340 msec at −20 mV to ∼6 msec at +80 mV, whereas closed times were unaffected. The channel was not Ca2+-dependent. Channel activity was blocked by disulfonic stilbenes, arylaminobenzoates, zinc, and cadmium. Single-channel conductance was sensitive to trans pH, ranging from ∼190 pS at pH 5.5 to ∼60 pS at pH 9.0. These characteristics are different from those previously described for Cl− channels from skeletal or cardiac muscle SR.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00233541
