Modifications of current properties by expression of a foreign potassium channel gene in Xenopus embryonic cells |
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Authors: | A E Spruce W J Moody |
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Institution: | (1) Cell Physiology Laboratory, Boys Town National Research Hospital, 555 North 30th Street, 68131 Omaha, NE |
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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 cm2, and I
sc was 587±30 A/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 A/(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 A/(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.The authors wish to thank Drs. Daniel C. Marcus, Zhjiun Shen and Hiroshi Sunose for helpful discussions. This work was supported by grants NIH-R29-DC01098 and NIH-R01-DC00212. |
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Keywords: | Labyrinth Slowly activating K+ channel IsK channel MinK channel pH |
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