Fig. 5.

NKCC1 transports less Na⁺ than K⁺. Ouabain-resistant unidirectional ⁸⁶Rb and ²²Na fluxes were measured in NKCC1 cRNA-injected oocytes incubated in isosmotic (200 mosM) and hyperosmotic (265 mosM) solution, in the presence and absence of 20 μM bumetanide. Fluxes were also measured in oocytes coinjected with NKCC1 cRNA and constitutively active SPAK cRNA in isosmotic solution. Bumetanide-sensitive K⁺ and Na⁺ influxes are expressed in nanomoles cation·oocyte⁻¹·h⁻¹. Bars represent means ± SE (n = 20–25 oocytes). SEs for bumetanide-sensitive flux were calculated as square roots of (SEM₁² n₁⁻¹ + SEM₂² n₂⁻¹). Cl⁻ influxes (dotted lines) are taken from earlier studies (17). Shaded bars indicate the classical 1Na⁺:1K⁺:2Cl⁻¹ component of transport.