Figure 5. NKCC1-mediated K⁺ loss in oocytes under hypertonicity.

A, K⁺ loss per oocyte per hour in the absence and presence of 20 μm bumetanide. B, log-linear plot of ⁸⁶Rb content (in counts min⁻¹) in oocytes as a function of time. The slopes of potassium-free (filled circles) and potassium-containing (filled squares) represent the rate constants of K⁺ efflux, expressed in min⁻¹. The initial rapid and non-linear component represents the washout of the external ⁸⁶Rb, that is the radioactivity which is carried over with the oocytes when the device is moved from the uptake solution to the washout solutions. The dashed line represents an initially slower linear component of K⁺ efflux which indicates the lag-time of NKCC1 activation by hypertonicity when the oocytes are transferred from the isotonic ⁸⁶Rb-containing L15 medium to the hypertonic efflux medium.