Article Figures & Data
Figures
- Figure 1.
Inhibition of GDPs with weak acids is not related to changes in the metabolic state of mitochondria. A, Weak acids l- and d-lactate (L-lac and D-lac, respectively; 5 mm), as well as propionate (Prop, 1 mm), inhibit GDP activity. Data show the normalized GDP frequencies (Norm. DGP freq.) (±SEM) from 12, 9, and 6 slices, respectively. In all individual field-potential recordings, the sliding average of GDPs was calculated over a bin of 120 s, with a sliding interval of 15 s. Insets show original traces bandpass filtered at 0.2–25 Hz from an experiment where 5 mm l-lactate was applied. Scale bars for insets, 5 s/25 μV. B, Bumetanide (bume; 10 μm) reversibly abolished GDP activity in the continuous presence of 5 mm l-lactate (recording obtained 40 min after the beginning of lactate application; bandpass, 2.5–25 Hz). C, Glucose depletion causes a progressive suppression of GDPs in the presence of 5 mm l-lactate. Glucose was replaced with an equimolar amount of sucrose. GDP frequency fully recovered when glucose concentration was restored to normal. Figure illustrates the sliding GDP frequency averaged from seven slices.
- Figure 2.
Depolarizing GABA actions are not attributable to deficient mitochondrial energy metabolism. A, Mitochondrial membrane potential is not affected by 5 mm l-lactate (L-lac) or when l-lactate is replaced with d-lactate (D-lac). The bar diagrams represent the normalized Rh123 fluorescence of CA3 pyramidal neurons (+SEM, number of slices shown in brackets). Inset, CA3 pyramidal neurons in a slice preparation loaded with Rh123. Scale bar, 10 μm. B, A specimen recording showing the lack of effect when 5 mm l-lactate in standard solution is replaced with 5 mm d-lactate. C, Glucose (gluc) depletion causes a gradual and reversible depolarization of the mitochondrial membrane potential. When FCCP (4 μm) is applied to uncouple mitochondrial membrane potential, a profound increase in fluorescence intensity takes place, reflecting a depolarization of mitochondria.
- Figure 3.
Weak acids and elevated CO2 content evoke an intracellular acidosis. A, Bath application of 5 mm l- or d-lactate (L-lac and D-lac, respectively) induces an intracellular acidification comparable to that obtained with 1 mm propionate (Prop). A larger pHi transient is evoked with 5 mm propionate and by increasing CO2 from 5% to 8%. Original pH traces showing averaged responses from two to five neurons. B, Combined data from pHi recordings of the above type (number of slices in brackets). C, CO2 (8%) transiently blocks GDPs and causes a prompt intracellular acidification. Top, Field-potential recording (bandpass, 2.5–25 Hz). Bottom, pHi measurement from two neurons, baseline pHi 7.16. Downward deflection indicates intracellular acidification. D, Inhibition of GDPs by l- and d-lactate and propionate or with elevated CO2 shows a strict correlation with the fall in pHi. Reduction in the normalized GDP frequency (Norm. GDP freq.) is plotted versus the amplitude of the evoked intracellular acidification (r = −0.97).
