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Cl- channels in basolateral renal medullary vesicles. IX. Channels from mouse MTAL cell patches and medullary
W B Reeves1, C J Winters, D M Filipovic
1Department of Internal Medicine, University of Arkansas College of Medicine, Little Rock, USA.
Abstract:
The experiments reported herein compared Cl- channels fused into bilayers from rabbit outer medullary vesicles with Cl- channels in excised patches of basolateral membranes from cultured mouse medullary thick ascending limb (MTAL) cells and evaluated whether the latter were plausible candidates for the Cl- channels mediating net NaCl absorption in microperfused mouse MTAL segments. The unique signature characteristics of Cl- channels incorporated into lipid bilayers from outer medullary vesicles include activation of open probability (Po) by increases in the Cl- concentrations bathing intracellular faces; activation of Po by protein kinase A (PKA) + ATP, when the Cl- concentrations bathing intracellular faces are low; and no effect of PKA + ATP on Po with high cytoplasmic-face Cl- concentrations. These same properties were observed in Cl- channels studied using excised patches of basolateral membranes from mouse MTAL cells. Moreover, in both bilayers and in excised patches, the sharpest fractional increase in Cl- channel Po occurred with cytosolic-face Cl- concentration increases to values similar to the antidiuretic hormone (ADH)-dependent values of intracellular Cl- activity in microperfused mouse MTAL segments, and these fractional Po increases were adequate to account quantitatively for the ADH-dependent increase in basolateral membrane Cl- conductance in microperfused mouse MTAL segments. Thus the excised-patch basolateral Cl- channels reported here are reasonable candidates for those mediating net Cl- absorption in the MTAL.
Insights
This study identified chloride channels in mouse kidney cells that are activated by protein kinase A (PKA) and antidiuretic hormone (ADH). These channels are crucial for NaCl absorption in the thick ascending limb of the kidney nephron.
Area of Science:
- Nephrology
- Molecular Physiology
- Ion Transport
Background:
- The thick ascending limb (TAL) of the kidney nephron plays a critical role in NaCl reabsorption.
- Chloride channels in the basolateral membrane of TAL cells are essential for this process.
- Understanding the specific characteristics of these channels is key to understanding kidney function.
Purpose of the Study:
- To compare chloride channels from rabbit outer medullary vesicles with those from mouse medullary thick ascending limb (MTAL) cells.
- To determine if MTAL basolateral membrane chloride channels are responsible for net NaCl absorption.
- To investigate the regulatory mechanisms of these chloride channels.
Main Methods:
- Incorporation of Cl- channels into lipid bilayers from rabbit outer medullary vesicles.
- Electrophysiological studies of Cl- channels in excised patches of basolateral membranes from cultured mouse MTAL cells.
- Comparison of channel properties, including open probability (Po) regulation by Cl- concentration and protein kinase A (PKA) + ATP.
Main Results:
- Cl- channels from both sources exhibited similar regulatory properties.
- Activation of open probability (Po) by intracellular Cl- concentration increases.
- Regulation by PKA + ATP was dependent on intracellular Cl- concentrations.
- Observed Po increases quantitatively matched ADH-dependent increases in MTAL basolateral membrane Cl- conductance.
Conclusions:
- Cl- channels in excised patches of mouse MTAL basolateral membranes share key characteristics with those from rabbit outer medullary vesicles.
- These channels are plausible candidates for mediating net NaCl absorption in microperfused mouse MTAL segments.
- The findings support the role of these specific Cl- channels in regulating kidney salt reabsorption.