Effect of ouabain on volume and chemosensitivity of Xenopus oocytes injected with rat brain mRNA.

Xenopus oocytes injected with rat brain RNA were voltage-clamped using a 2-electrode technique. At 4-10 days post-injection the oocytes responded to applications of 10(-6) M to 10(-4) M gamma-aminobutyric acid (GABA), L-kainate and L-glutamate. All 3 compounds evoked inward currents. At 10(-4) ouabain alone evoked an inward current of 4-6 nA at -60 mV, but had no effect on membrane conductivity (ca. 5 microS). In ouabain-containing saline the responses to GABA, L-kainate and L-glutamate were increased by 80-120%, 20-30% and 20-40%, respectively, in both folliculated and defolliculated oocytes. These changes were not accompanied by shifts in the reversal potentials for the agonist-induced membrane currents. At 10(-4) M ouabain also increased oocyte weight and volume. It is proposed that ouabain, by increasing oocyte volume, increases the area of oocyte membrane containing receptors which is accessible to exogenously applied compounds.