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A hydrodynamic mechanosensory hypothesis for brush border microvilli
P Guo1, A M Weinstein, S Weinbaum
1CUNY Graduate School and Center for Biomedical Engineering, the City College of the City University of New York, New York 10031, USA.
American Journal of Physiology. Renal Physiology
|September 21, 2000
Summary
Kidney proximal tubule cells may sense fluid flow using microvilli. These structures act as mechanosensors, with their tips bending to detect changes in flow rate and regulate reabsorption.
Area of Science:
- Nephrology
- Biophysics
- Cell Biology
Background:
- Proximal tubule sodium (Na+) and bicarbonate (HCO3-) reabsorption is flow-dependent, crucial for glomerulotubular balance.
- The cellular mechanism for sensing axial fluid flow in the proximal tubule remains unclear.
Purpose of the Study:
- To investigate the hypothesis that microvilli act as mechanosensors of fluid flow in the proximal tubule.
- To quantitatively model the physical forces and deformations experienced by microvilli under luminal flow.
Main Methods:
- Development of an elastohydrodynamic model to simulate microvilli response to fluid flow.
- Prediction of forces, torques, and elastic bending deformation along individual microvilli.
Main Results:
- Microvilli spacing creates near-zero axial velocity within the brush border, with drag forces significantly exceeding apical membrane shear forces.
- The majority of drag force (74%) on microvilli occurs near the tip.
- Luminal flow induces microvillar tip deflection, with bending proportional to flow rate and dependent on microvillus length and actin filament strength.
Conclusions:
- Microvilli are physically suited to function as mechanosensors of luminal flow in the proximal tubule.
- The dense arrangement and physical properties of microvilli amplify torque in response to fluid drag, potentially signaling flow changes to the cell.
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