title: pH regulation in horizontal cells of the skate retina.
abstract: To examine the mechanisms by which horizontal cells regulate intracellular pH (pHi), measurements were recorded from isolated cells enzymatically dissociated from the skate retina utilizing the pH-sensitive dye BCECF. In a HCO3--containing Ringer solution, steady-state pHi was 7.32+/-0.13 (mean+/-S.D., n=70). Recovery from acidification was examined using the NH4+ prepulse technique. When NH4+ was removed from the extracellular solution, pHi dropped rapidly to approximately 0.3 pH units below the initial baseline, and then recovered at an initial rate of approximately 0.072 pH units/min. During recovery of pHi after the acid load, the removal of Na+ or the addition of amiloride from a HCO3--free extracellular solution reduced the rate of recovery by 79%+/-11% and 69%+/-14%, respectively. In the presence of DIDS, which inhibits primarily anion transport, or during the removal of Na+, the recovery from acidification was reduced by 83%+/-10% and 70%+/-11%, respectively, as compared to the control value in HCO3--containing solution. These results suggest that the skate horizontal cell possesses a Na/H exchanger as well as a Na+-and HCO3--dependent mechanism for removal of excess acid. Removal of HCO3- or Cl- from the extracellular solution had little effect on pHi, but removing external Na+ induced a marked decrease in pHi that fell at an initial rate of approximately 0.3 pH units min-1. This rate of acidification was decreased by 58%+/-19% in the presence of DIDS (500 micron) and reduced by 28%+/-13% with the addition of amiloride (2 mm). Thus, Na- and HCO3-dependent transport was about 2-fold more active than Na/H exchange during low Na+-induced acidification. The intrinsic pH-buffer capacity, determined from the pHi change induced by incremental reductions in the [NH4+] of the extracellular solution, was 24.2 mm/pH unit at the horizontal cell's resting pHi. Moreover, pHi was relatively insensitive to changes in membrane potential; in experiments under whole-cell voltage clamp (-70 mV), intracellular pH remained constant during depolarizing voltage swings to -30 mV or +30 mV, as well as during hyperpolarizing pulses to -90 or -110 mV.
authors.affiliation: Lions of Illinois Eye Research Institute, Department of Ophthalmology and Visual Sciences, University of Illinois College of Medicine, 1855 West Taylor Street, Chicago, Illinois 60612, USA.
authors.forename: L
authors.initials: L
authors.lastname: Haugh-Scheidt
authors.forename: H
authors.initials: H
authors.lastname: Ripps
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D002255:Carbonic Acid / Q000494:pharmacology; D004594:Electrophysiology; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D008564:Membrane Potentials / Q000502:physiology; D011188:Potassium / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012160:Retina / Q000166:cytology / Q000502:physiology*; D012860:Skates, Fish / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology
chemical_list: D000644:Quaternary Ammonium Compounds; D002255:Carbonic Acid; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium