CIC chloride channels are important in diverse physiological functions such as transepithelial transport, cell volume regulation, excitability, and acidification of intracellular organelles. We have investigated the expression of CLC-7 in oocytes from Xenopus laevis with the two electrode voltage clamp technique and Western blot analysis. Using a specific antibody against CLC-7, we found an approximate to80 kDa protein in oocytes, previously injected with CLC-7-cRNA. In voltage clamp experiments on CIC-7-cRNA-injected oocytes, no current changes were detected at normal pH (7.4). However, acidification of the Ringer solution to pH values between 6 and 4 revealed strong currents which reversed at about -15 mV (30 mV positive to the normal resting potential) and showed strong outward rectification. We therefore suggest that CIC-7 in oocytes is a functional chloride current at acidic p. Since CIC-7 is also found in neuronal tissues and was upregulated in a rat pain model, we suggest a role of CLC-7 also for nociception and pain. (C) 2002 Elsevier Science (USA).