ISSN:
1432-1424
Keywords:
Labyrinth
;
Slowly activating K+ channel
;
IsK channel
;
MinK channel
;
pH
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract The pH-sensitivity of transepithelial K+ transport was studied in vitro in isolated vestibular dark cell epithelium from the gerbil ampulla. The cytosolic pH (pH iwas measured microfluorometrically with the pH-sensitive dye 2′,7′-bicarboxyethyl-5(6)-carboxyfluorescein (BCECF) and the equivalent short-circuit current (I sc), which is a measure for transepithelial K+ secretion, was calculated from measurements of the transepithelial voltage (V t)and the transepithelial resistance (R t) in a micro-Ussing chamber. All experiments were conducted in virtually HCO 3 − -free solutions. Under control conditions, pH iwas 7.01±0.04 (n=18), V twas 9.1±0.5 mV, R t16.7±0.09 Ωcm2, and I sc was 587±30 μA/cm2 (n=49). Addition of 20 mm propionate− caused a biphasic effect involving an initial acidification of pH i, increase in V tand I sc and decrease in R tand a subsequent alkalinization of pH i, decrease of V tand increase of R t. Removal of propionate− caused a transient effect involving an alkalinization of pH i, a decrease of V tand I sc and an increase in R t. pH iin the presence of propionate− exceeded pH iunder control conditions. Effects of propionate − on V t, R tand I sc were significantly larger when propionate− was applied to the basolateral side rather than to the apical side of the epithelium. The pH i-sensitivityof I sc between pH 6.8 and 7.5 was −1089 μA/(cm2 · pH-unit) suggesting that K+ secretion ceases at about pH i7.6. Acidification of the extracellular pH (pH o)caused an increase of V tand I sc and a decrease of R tmost likely due to acidification of pH i. Effects were significantly larger when the extracellular acidification was applied to the basolateral side rather than to the apical side of the epithelium. The pH osensitivity of I sc between pH 7.4 and 6.4 was −155 μA/(cm2 · pH unit). These results demonstrate that transepithelial K+ transport is sensitive to pH iand pH oand that vestibular dark cells contain propionate− uptake mechanism. Further, the data suggest that cytosolic acidification activates and that cytosolic alkalinization inactivates the slowly activating K+ channel (I sK)in the apical membrane. Whether the effect of pH ion the I sK channel is a direct or indirect effect remains to be determined.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00234523
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