Figure 7. Effects on oocyte volume of abrupt changes in clamp voltage.

An rSGLT1-expressing oocyte was exposed, isosmotically, to 2 mm of α-MDG under voltage clamp conditions (−50 mV), as in Fig. 2. This resulted in an I_C of 840 nA. After about 60 s (at the vertical dashed line) the clamp voltage was jumped to +20 mV and I_C changed abruptly to 390 nA. The corresponding reduction in the rate of volume change corresponds to a change in influx of water (J_H2O=ΔV_T/dt) from 41 pl s⁻¹ to 28 pl s⁻¹. The thin line was obtained from simulation of the experiment by the model given in the Appendix. Radius of the oocyte was 0.064 cm. The difference in the two rates of swelling of 13 pl s⁻¹ (41–28) and the corresponding change in I_C of 450 nA (840–390) corresponds to a CR of 388.