Membrane cholesterol extraction decreases Na+ transport in A6 renal epithelia.
In this study, we have investigated the dependence of Na+ transport regulation on membrane cholesterol content in A6 renal epithelia. We continuously monitored short-circuit current (Isc), transepithelial conductance (GT), and transepithelial capacitance (CT) to evaluate the effects of cholesterol extraction from the apical and basolateral membranes in steady-state conditions and during activation with hyposmotic shock, oxytocin, and adenosine. Cholesterol extraction was achieved by perfusing the epithelia with methyl-beta-cyclodextrin (mbetaCD) for 1 h. In steady-state conditions, apical membrane cholesterol extraction did not significantly affect the electrophysiological parameters; in contrast, marked reductions were observed during basolateral mbetaCD treatment. However, apical mbetaCD application hampered the responses of Isc and GT to hypotonicity, oxytocin, and adenosine. Analysis of the blocker-induced fluctuation in Isc demonstrated that apical mbetaCD treatment decreased the epithelial Na+ channel (ENaC) open probability (Po) in the steady state as well as after activation of Na+ transport by adenosine, whereas the density of conducting channels was not significantly changed as confirmed by CT measurements. Na+ transport activation by hypotonicity was abolished during basolateral mbetaCD treatment as a result of reduced Na+/K+ pump activity. On the basis of the findings in this study, we conclude that basolateral membrane cholesterol extraction reduces Na+/K+ pump activity, whereas the reduced cholesterol content of the apical membranes affects the activation of Na+ transport by reducing ENaC Po.
Balut
Corina
C
Laboratory of Physiology, Hasselt Univ., Agoralaan 1D, B-3590 Diepenbeek, Belgium.
Steels
Paul
P
Radu
Mihai
M
Ameloot
Marcel
M
Driessche
Willy Van
WV
Jans
Danny
D
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D016477:Artifacts; D002460:Cell Line; D016764:Cell Polarity / Q000502:physiology; D002784:Cholesterol / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D053503:Epithelial Sodium Channels; D007038:Hypotonic Solutions / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007668:Kidney / Q000166:cytology*; D008563:Membrane Lipids / Q000378:metabolism*; D009997:Osmotic Pressure; D010121:Oxytocin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014982:Xenopus laevis; D047392:beta-Cyclodextrins / Q000494:pharmacology
D053503:Epithelial Sodium Channels; D007038:Hypotonic Solutions; D008563:Membrane Lipids; D015222:Sodium Channels; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D010121:Oxytocin; D002784:Cholesterol; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D000241:Adenosine; D011188:Potassium