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. 2019 Sep 5;9:218. doi: 10.1038/s41398-019-0551-1

Fig. 2. Spermine and pH effects on native GABA currents.

Fig. 2

a Non-transplanted oocytes were unresponsive to extracellular perfusion of GABA (30 μM) but elicited concentration-dependent biphasic responses to perfusion of spermine when the pH of the Ringer’s solution was not readjusted to 7.4 after addition of spermine (pH (−)). b, c. Oocyte microtransplanted with synaptic membranes (MSM) from subject S3 showing responses to 30 μM GABA (EC25 for S3) and to the co-application of 30 μM GABA with different concentrations of spermine pH(−). Notice that an initial inward current (arrow in C), elicited during co-application of GABA and 3 mM spermine pH(−), was cut short by the appearance of a large outward current. d Preincubation with 3 mM spermine pH(−) inhibited the responses to 30 μM GABA. e GABA responses (30 μM) in microtransplanted oocytes were inhibited during perfusion of 3 mM spermine pH(−). However, when the pH was titrated to 7.4 (pH( + )) GABA responses were minimally reduced. f Perfusion of extracellular solution, titrated to pH 10, and to the same oocyte shown in E, elicited a slow inward current and reduced GABA responses to 9.9 ± 0.4% of the control. g Plot summarizing the effects of spermine on GABA’s EC25. Circles indicate the mean ± s.e.m., of GABA currents derived from all subjects when the pH of the Ringer’s solution was not readjusted after addition of spermine (pH (−)). Spermine at concentrations of 100 µM, 1 mM, and 3 mM, changed the pH to 7.56, 8.9, and 10.3, respectively. Black circles represent the effects produced by co-application of spermine and GABA, and white circles the added effects of the preincubation with spermine for at least 10 s, or when the baseline current was stable. The white triangle indicates the effects of 3 mM spermine, preincubated and then co-applied with GABA, in Ringer’s solution with the pH fixed at 7.4 (pH ( + )). The number in parenthesis indicates the number of oocytes tested. h Comparison of the effects produced by high concentration of spermine with and without readjusting the pH, and with solutions without spermine but high pH in subject S3 which had the strongest effect to 3 mM spermine pH(−)