Acid efflux from retinal glial cells generated by sodium bicarbonate cotransport

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Abstract

Sodium bicarbonate cotransport was studied in freshly dissociated Muller cells of the salamander retina. Variations in intracellular and extracellular pH evoked by elevating extracellular potassium concentration ([K+](o)) were recorded. Intracellular pH was measured by standard ratio imaging of the pH- sensitive dye BCECF, whereas extracellular pH was monitored by imaging BCECF fixed to coverslips under dissociated cells. Increasing [K+ ](o) from 2.5 to 50 mM resulted in an intracellular alkalinization. The rate of alkalinization, 0.047 pH units/min, was reduced to 42% of control when HEPES was substituted for HCO3 and was reduced to 36% of control by the addition of 0.5 mM DIDS, a Na+/HCO3 cotransport blocker. The K+-evoked alkalinization was Cl--independent and was not substantially reduced by amiloride or bumetanide. Increasing [K+](o) to 50 mM also produced a rapid extracellular acidification, 0.01 to 0.05 pH units in amplitude. HEPES substitution and addition of 0.5 mM DIDS reduced the acidification to 7-8% of control, respectively. These results confirm the presence of a Na+/HCO3 cotransport system in salamander Muller cells and provide definitive evidence that glial cells can generate an extracellular acidification when [K+](o) is increased. The K+-evoked extracellular acidification measured beneath cell endfeet was 304% of the amplitude of the acidification beneath cell somata, confirming that cotransporter sites are preferentially localized to the endfoot. The carbonic anhydrase inhibitor benzolamide (2 x 10-5 M), which is poorly membrane permeant, increased the K+-evoked extracellular acidification to 269% of control, demonstrating that salamander Muller cells possess extracellular carbonic anhydrase.

Original languageEnglish (US)
Pages (from-to)159-168
Number of pages10
JournalJournal of Neuroscience
Volume16
Issue number1
StatePublished - Jan 1 1996

Keywords

  • BCECF
  • Muller cell
  • Na/HCO cotransport
  • glial cell
  • pH
  • retina
  • salamander

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