Isoform-specific function and distribution of Na/K pumps in the frog lens epithelium
J Gao, X Sun, V Yatsula, RS Wymore… - The Journal of membrane …, 2000 - Springer
J Gao, X Sun, V Yatsula, RS Wymore, RT Mathias
The Journal of membrane biology, 2000•SpringerEpithelial cells from the anterior and equatorial surfaces of the frog lens were isolated and
used the same day for studies of the Na/K ATPase. RNase protection assays showed that all
cells express α 1-and α 2-isoforms of the Na/K pump but not the α 3-isoform, however the α 2-
isoform dominates in anterior cells whereas the α 1-isoform dominates in equatorial cells.
The whole cell patch-clamp technique was used to record functional properties of the Na/K
pump current (IP), defined as the current specifically inhibited by dihydro-ouabain (DHO) …
used the same day for studies of the Na/K ATPase. RNase protection assays showed that all
cells express α 1-and α 2-isoforms of the Na/K pump but not the α 3-isoform, however the α 2-
isoform dominates in anterior cells whereas the α 1-isoform dominates in equatorial cells.
The whole cell patch-clamp technique was used to record functional properties of the Na/K
pump current (IP), defined as the current specifically inhibited by dihydro-ouabain (DHO) …
Abstract
Epithelial cells from the anterior and equatorial surfaces of the frog lens were isolated and used the same day for studies of the Na/K ATPase. RNase protection assays showed that all cells express α1- and α2-isoforms of the Na/K pump but not the α3-isoform, however the α2-isoform dominates in anterior cells whereas the α1-isoform dominates in equatorial cells. The whole cell patch-clamp technique was used to record functional properties of the Na/K pump current (I P ), defined as the current specifically inhibited by dihydro-ouabain (DHO). DHO-I P blockade data indicate the α1-isoform has a dissociation constant of 100 μm DHO whereas for the α2-isoform it is 0.75 μm DHO. Both α1- and α2-isoforms are half maximally activated at an intracellular Na+-concentration of 9 mm. The α1-isoform is half maximally activated at an extracellular K+-concentration of 3.9 mm whereas for the α2-isoform, half maximal activation occurs at 0.4 mm. Lastly, transport by the α1-isoform is inhibited by a drop in extracellular pH, which does not affect transport by the α2-isoform. Under normal physiological conditions, I P in equatorial cells is approximately 0.23 μA/μF, and in anterior cells it is about 0.14 μA/μF. These current densities refer to the area of cell membrane assuming a capacitance of around 1 μF/cm2. Because cell size and geometry are different at the equatorial vs. anterior surface of the intact lens, we estimate Na/K pump current density per area of lens surface to be around 10 μA/cm2 at the equator vs. 0.5 μA/cm2 at the anterior pole.
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