1. The influence of Cl‐ concentration and pH on gating of the skeletal muscle Cl‐ channel, ClC‐1, has been assessed using the voltage‐clamp technique and the Sf‐9 insect cell and Xenopus oocyte expression systems. 2. Hyperpolarization induces deactivating inward currents comprising a steady‐state component and two exponentially decaying components, of which the faster is weakly voltage dependent and the slower strongly voltage dependent. 3. Open probability (Po) and kinetics depend on external but not internal Cl‐ concentration. 4. A point mutation, K585E, in human ClC‐1, equivalent to a previously described mutation in the Torpedo electroplaque chloride channel, ClC‐0, alters the I‐V relationship and kinetics, but retains external Cl‐ dependence. 5. When external pH is reduced, the deactivating inward currents of ClC‐1 are diminished without change in time constants while the steady‐state component is enhanced. 6. In contrast, reduced internal pH slows deactivating current kinetics as its most immediately obvious action and the Po curve is shifted in the hyperpolarizing direction. Addition of internal benzoate at low internal pH counteracts both these effects. 7. A current activated by hyperpolarization can be revealed at an external pH of 5.5 in ClC‐1, which in some ways resembles currents due to the slow gates of ClC‐0. 8. Gating appears to be controlled by a Cl(‐)‐binding site accessible only from the exterior and, possibly, by modification of this site by external protonation. Intracellular hydroxyl ions strongly affect gating either allosterically or by direct binding and blocking of the pore, an action mimicked by intracellular benzoate.

The presence of perineural infiltration and lymphovascular invasion on histopathology is highly significant in predicting 5-year outcomes after pancreaticoduodenectomy for periampullary and pancreatic malignancies.

Regression of Barrett esophagus after fundoplication is more likely, and greater in extent, in patients who undergo ablation with APC. In most patients treated with APC the neosquamous mucosa remains stable at up to 5-year follow-up. The development of high-grade dysplasia only occurred in patients who were not treated with APC.

1 Using whole-cell patch-clamping and Sf-9 cells expressing the rat skeletal muscle chloride channel, rClC-1, the cellular mechanism responsible for the myotonic side e ects of clo®brate derivatives was examined. 2 RS-(+) 2-(4-chlorophenoxy)propionic acid (RS-(+) CPP) and its S-(7) enantiomer produced pronounced e ects on ClC-1 gating. Both compounds caused the channels to deactivate more rapidly at hyperpolarizing potentials, which showed as a decrease in the time constants of both the fast and slow deactivating components of the whole cell currents. Both compounds also produced a concentration-dependent shift in the voltage dependence of channel apparent open probability to more depolarizing potentials, with an EC 50 of 0.79 and 0.21 mM for the racemate and S- (7) enantiomer respectively. R-(+) CPP at similar concentrations had no e ect on gating. RS-(+) CPP did not block the passage of Cl 7 through the pore of rClC-1. 3 ClC-1 is gated by Cl 7 binding to a site within an access channel and S-(7) CPP alters gating of the channel by decreasing the a nity of this binding site for Cl 7 . Comparison of the EC 50 for RS-(+) CPP and S-(7) CPP indicates that R-(+) CPP can compete with the S-(7) enantiomer for the site but that it is without biological activity. 4 RS-(+) CPP produced the same e ect on rClC-1 gating when added to the interior of the cell and in the extracellular solution. 5 S-(7) CPP modulates the gating of ClC-1 to decrease the membrane Cl 7 conductance (G Cl ), which would account for the myotonic side e ects of clo®brate and its derivatives.

1. Gating of the skeletal muscle chloride channel (ClC-1) is sensitive to extracellular pH. In this study, whole-cell recording of currents from wild-type (WT) ClC-1 and a mutant, R304E, expressed in the Sf-9 insect cell line was used to investigate further the nature of the pHsensitive residues. 2. Extracellular Cd¥ produced a concentration-dependent block of WT ClC-1 with an IC50 of 1·0 ± 0·1 mÒ and a Hill coefficient of 2·0 ± 0·3. This block was sensitive to external pH, reducing at low pH, with an apparent pKa of 6·8 ± 0·1 and a Hill coefficient for proton binding of 3·0 ± 0·3. Anthracene-9-carboxylate (A-9-C) block of WT ClC-1 was also pH sensitive, increasing at low pH, with an apparent pKa of 6·4 ± 0·1 and a Hill coefficient for proton binding of 1·0 ± 0·2. 3. Compared with WT ClC-1, R304E had a lower affinity for Cd¥ (IC50, 3·0 ± 0·3 mÒ) but it had a similar Hill coefficient for transition metal ion binding. The Hill coefficient for proton binding to the Cd¥ binding site was reduced to 1·4 ± 0·3. In contrast, the A-9-C binding site in R304E showed the same pH sensitivity and affinity for the blocker as that seen in WT ClC-1. 4. ClC-1 has at least two binding sites for Cd¥, each of which has at least three residues which can be protonated. Binding of A-9-C is influenced by protonation of a single residue. Arg 304 is not sufficiently close to the A-9-C binding site to affect its characteristics, but it does alter Cd¥ binding, indicating that transition metal ions and aromatic carboxylates interact with distinct sites. 5. The block of ClC-1 by transition metal ions and the apparent pKa of this block, together with the apparent pKa for A-9-C block and gating are all compatible with the involvement of His residues in the pore and gate of ClC-1.