Regulation of Slick channels by small changes in cell volume.

In the upper panels, Slick channels were co-expressed with AQP1 in Xenopus laevis oocytes and were activated by a step protocol (−100 mV to +80 mV in 20 mV increments of 500 ms) from a holding potential of −80 mV (4 s). Currents were recorded in isotonic (A), hypotonic (B) or hypertonic (C) media. (D) shows the corresponding I/V relationships under isotonic (black), hypotonic (blue) and hypertonic (red) conditions. Control experiments for native, un-injected oocytes (UI, green) and oocytes only expressing AQP1 (violet) are also shown. In (E) maximal currents were measured at the end of the depolarization to +80 mV under isotonic, hypotonic and hypertonic buffers and the currents were normalized to the current measured at isotonic conditions. Data points in panels (D) and (E) show the mean of 10 independent experiments ± S.E.M. (F) displays a current trace over time for a representative oocyte expressing Slick and AQP1. The expressed Slick channels were activated by depolarization to +80 mV (500 ms) from a holding potential of −80 mV (3 s). The Figure shows the current measured at the end of the depolarization period as a function of time. Changes from isotonic medium to hypo- or hypertonic media are marked with arrows in the figure (the apparent delay from change in medium (arrows) to changes in the recorded currents reflect the “dead volume” in the flow system).