PT  - JOURNAL ARTICLE
AU  - EA Newman
TI  - Acid efflux from retinal glial cells generated by sodium bicarbonate cotransport
AID  - 10.1523/JNEUROSCI.16-01-00159.1996
DP  - 1996 Jan 01
TA  - The Journal of Neuroscience
PG  - 159--168
VI  - 16
IP  - 1
4099  - http://www.jneurosci.org/content/16/1/159.short
4100  - http://www.jneurosci.org/content/16/1/159.full
SO  - J. Neurosci.1996 Jan 01; 16
AB  - Sodium bicarbonate cotransport was studied in freshly dissociated Muller cells of the salamander retina. Variations in intracellular and extracellular pH evoked 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.