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Membrane currents controlled by physical forces in cultured mesangial cells
W Craelius1, M J Ross, D R Harris
1Department of Biomedical Engineering, Rutgers University, Piscataway, New Jersey.
Abstract:
Mechanically-activated ion channels (MACs) of cultured rat mesangial cells were stimulated by applying suction to patch pipets or by exposing cells to hypoosmotic media. MAC density was estimated as 1.5 +/- 0.4 per mu 2. In the absence of any stimulus, MAC open probabilities (N * P) were < 0.0001 increasing as a function of stretch or extracellular hypoosmolarity. Single channel mean open time during stretch increased with patch depolarization whereas hyperpolarization of the membrane delayed MAC inactivation. Ionic conductance of MACs, based on average slope conductances at hyperpolarized potentials, was 76 pS in high external K+ (N = 5) and 40 pS in high external Na+ (N = 8). PK+/PNa+ was estimated to be 4.7. MACs did not permeate Cl-, at least outwardly. Whole cell currents in response to voltage steps applied to resting cells in control conditions were approximately ohmic between -120 mV and 40 mV and were linearly and reversibly dependent on extracellular osmolarity. Our results demonstrate that: (1) MACs can be activated by both negative hydrostatic pressures applied to the pipet and by osmotic gradients; (2) MAC kinetic behavior is sensitive to membrane potential; (3) MACs may participate in cellular responses to physical forces.
Insights
Mechanically-activated ion channels (MACs) in rat mesangial cells respond to physical forces like stretch and osmotic changes. These channels
Area of Science:
- Cell biology
- Biophysics
- Renal physiology
Background:
- Mechanically-activated ion channels (MACs) are crucial for cellular mechanotransduction.
- Understanding MACs in mesangial cells is vital for kidney function and disease research.
Purpose of the Study:
- To investigate the activation, kinetics, and ion selectivity of MACs in cultured rat mesangial cells.
- To determine the role of MACs in cellular responses to mechanical and osmotic stimuli.
Main Methods:
- Patch-clamp electrophysiology was used to record single-channel and whole-cell currents.
- Cells were subjected to mechanical stretch (suction) and osmotic gradients (hypoosmotic media).
- Membrane potential was manipulated to study MAC kinetic behavior.
Main Results:
- MACs were activated by both negative hydrostatic pressure and extracellular hypoosmolarity.
- MAC open probability increased with stretch and hypoosmolarity.
- Channel kinetics were sensitive to membrane potential, with depolarization increasing open time and hyperpolarization delaying inactivation.
- Ionic conductance was measured, with PK+/PNa+ estimated at 4.7; MACs did not significantly permeate chloride.
- Whole-cell currents showed ohmic behavior and were dependent on extracellular osmolarity.
Conclusions:
- MACs in rat mesangial cells are activated by physical forces, including stretch and osmotic gradients.
- MACs exhibit voltage-dependent gating kinetics.
- These findings suggest MACs play a role in mesangial cell responses to mechanical stress and osmotic challenges, potentially impacting renal function.