Abstract
The effect of picomolar concentrations of angiotensin II (AII) was investigated in isolated perfused rabbit renal proximal tubules using conventional or pH-sensitive intracellular microelectrodes. Under control conditions cell membrane potential (V b) and cell pH (pHi) averaged −53.8±1.9 mV (mean±SEM,n=49) and 7.24±0.01 (n=10), respectively. AII (at 10−11 mol/l), when applied from the bath (but not when applied from the lumen perfusate), produced the following effects: approximately 85% of the viable tubules responded with a small depolarization (+ 5.5±0.4 mV,n=43) which was accompanied in half of the pHi measurements by a slow acidification (ΔpHi=−0.03±0.01,n=5). The remaining 15% responded with a small hyperpolarization (ΔVb=−3.1±0.4 mV,n=6). All changes were fully reversible and repeatable. Experiments with fast changes in bath HCO3 or K concentrations, as well as measurements of the basolateral voltage divider fraction in response to transepithelial current flow, explain these observations as stimulation of a basolateral Na-HCO3 cotransporter and of a basolateral K conductance. Both counteract in their effect onV b, but can be individuated by blocker experiments with 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS) and barium. Both the stimulation of Na-HCO3 cotransport and the stimulation of the K conductance may result from down-regulation of the level of cyclic adenosine monophosphate in the cell.
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Coppola, S., Frömter, E. An electrophysiological study of angiotensin II regulation of Na-HCO3 cotransport and K conductance in renal proximal tubules. Pflügers Arch. 427, 143–150 (1994). https://doi.org/10.1007/BF00585953
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DOI: https://doi.org/10.1007/BF00585953