The buffer commonly used for chloride efflux measurements in this laboratory is that described in Peterson and Cramer (57). The buffer composition is 10 mM DMG, 100 mM choline nitrate, 2 mM Ca(N03)2. Choline nitrate is formed from choline bicarbonate (Sigma) and nitric acid. The buffer is degassed for at least 1 h and titrated to the appropriate pH with NaOH. Other chloride-free buffers are also suitable for measurement, provided their ionic strength is similar to that used for vesicle preparation.
The protein sample should be in a buffer that is chloride free, if possible, and should also lack any compounds which would interfere with electrode response. (3-Mercaptoethanol has been found to especially perturb electrode response (S. L. Schendel and J. C. Reed, unpublished results).
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