Interactions of pH and K+ conductance in cultured bovine retinal pigment epithelial cells

Abstract

Passive ion transport properties were studied in confluent monolayers of cultured bovine retinal pigment epithelial cells using intracellular microelectrode technique. The mean stable intracellular (designated by subscript i) potential was -59.1 +/- 0.8 (SE) mV. Extracellular (designated by subscript o) acidification induced a depolarization, whereas alkalinization induced a hyperpolarization. These effects were observed both in bicarbonate-free as well as in HCO3- Ringer (pHo changed by varying [HCO3-]o at constant pCO2). Acidification of pHi (changed by addition and removal of butyrate, CO2 or NH3) also caused a depolarization. Complete removal of HCO3-/CO2 at constant pHo caused a hyperpolarization. K+ transference, checked by applying high K+o, increased with K+o. It decreased with both extra and intracellular acidification and increased with alkalinization. In the presence of Ba2+, voltage reactions to changes in either pHo or pHi were greatly reduced. Depolarization by 40 mM K+ caused a similar reduction. It is suggested that K+ conductance of bovine retinal pigment epithelial cells is reduced by either intra- or extracellular acidification at normal [K+]o. Depolarization by high K+ induces an increase in K+ transference and reduces pH sensitivity.

Contrasting Action of H⁺ and Ca²⁺ on K⁺ Transport in the Diluting Segment of Frog Kidney

“…the Na+-K* pump was most sensitive to Ca2+ depletion at pH 8.0. Discussion pH-sensitive K+ channels have been de scribed in various cell types: in retinal pig ment epithelial cells [15], pancreatic B cells [2], mouse astrocytes [31], mammalian kid ney cells [6,11], and in cells of amphibian diluting segment [7,13,17,23,27,32], Fur thermore, data have been published on the pH sensitivity of the Na+-K+-ATPase [14,26,31,32], The results of our experiments are consistent with these studies. Although the intracellular pH has not been evaluated in our study, we assume that changes in extracellular pH are modifying, to some ex tent, the cytoplasmic pH [15,31,32).…”

“…After this, we restarted the perfusion with the same solution and perfused for another 10 min. 15 s before the perfusion was stopped again, we added Ba;* (3 mmol/1) to the perfusion solution in order to inhibit the K' channels [14,15,20,28]. By this treat ment, the rate o f K ' uptake into the cells (via the Na*-K' ATPase) could be disclosed, as indicated by the change of VK, and recorded by the K*-selective ma croelectrode for 2 min.…”

“…as suming that variations of the extracellular pH lead to concomitant (hence quantita tively different) changes in intracellular pH [15,31). The physiological pH of frog plasma is about 7.8.…”

Use of Diethyl(2-methylpyrrolidin-2-yl)phosphonate as a Highly Sensitive Extra- and Intracellular 31P NMR pH Indicator in Isolated Organs

“…4). This acid-load technique, which results in a selective acidification of the extracellular compartment by the freely membranepermeable isobutyric acid, has been developed to study the mechanisms of proton transport from the cytosol (47). In a recent study using this technique in isolated rat livers, the role of the Na ϩ -HCO 3 Ϫ symport has been found predominant in maintaining cytosolic pH homeostasis (13).…”

Further studies of electrogenic Na+/HCO cotransport in glial cells of necturus optic nerve: Regulation of pHi

“…Inside the cell, C02 is hydrated to HzC03 and dissociates into H+ and HCO;, thereby causing an acidification (Roos and Boron, 1981). This acidification may alter pHsensitive conductances (e.g., Keller et al, 1986) and decrease Ba++ binding by titrating barium binding sites in the K+-channel. The effect of CO, influx was eliminated by raising bath [HCOgI at constant COz (i.e., variable pH); this protocol is associated with an intracellular alkalinization whose magnitude depends on the extent of membrane transport processes for HCO; (Boron and Boulpaep, 1983b).…”