A Tool for Computation of Changes in Na+, K+, Cl− Channels and Transporters Due to Apoptosis by Data on Cell Ion and Water Content Alteration

Monovalent ions are involved in a vast array of cellular processes. Their movement across the cell membrane is regulated by numerous channels and transporters. Identification of the pathways responsible for redistribution of ions and cell water in living cells is hampered by their strong interdependence. This difficulty can be overcome by computational analysis of the whole cell flux balance. Our previous computational studies were concerned with monovalent ion fluxes in cells under the conditions of balanced ion distribution or during transition processes after stopping the Na+/K+ pump. Here we analyze a more complex case—redistribution of ions during cell apoptosis when the parameters keep changing during the process. New experimental data for staurosporine-induced apoptosis of human lymphoma cells U937 have been obtained: the time course of changes in cellular K+, Na+, Cl−, and water content, as well as Rb+ fluxes as a marker of the Na/K pump activity. Using a newly developed computational tool, we found that alteration of ion and water balance was associated with a 55% decrease in the Na+/K+-ATPase rate coefficient over a 4-h period, with a time-dependent increase in potassium channel permeability, and a decrease in sodium channel permeability. The early decrease in [Cl−]i and cell volume were associated with an ~5-fold increase in chloride channel permeability. The developed approach and the presented executable file can be used to identify the channels and transporters responsible for alterations of cell ion and water balance not only during apoptosis but in other physiological scenarios

Automatic processing system for shadowgraph and interference patterns

The design and operation of an automatic system for the processing of shadowgraph and interference images are described. The system includes a two-coordinate processing table with an optical system for the projection of transparent images onto the photodetector, an image filter in the photodetector field, and a device for controlling the movement of the table and transmitting information to the minicomputer

Computation of Pump-Leak Flux Balance in Animal Cells

Background/Aims: Many vital processes in animal cells depend on monovalent ion transport across the plasma membrane via specific pathways. Their operation is described by a set of nonlinear and transcendental equations that cannot be solved analytically. Previous computations had been optimized for certain cell types and included parameters whose experimental determination can be challenging. Methods: We have developed a simpler and a more universal computational approach by using fewer kinetic parameters derived from the data related to cell balanced state. A file is provided for calculating unidirectional Na+, K+, and Cl- fluxes via all major pathways (i.e. the Na/K pump, Na+, K+, Cl- channels, and NKCC, KC and NC cotransporters) under a balanced state and during transient processes. Results: The data on the Na+, K+, and Cl- distribution and the pump flux of K+ (Rb+) are obtained on U937 cells before and after inhibiting the pump with ouabain. There was a good match between the results of calculations and the experimentally measured dynamics of ion redistribution caused by blocking the pump. Conclusion: The presented approach can serve as an effective tool for analyzing monovalent ion transport in the whole cell, determination of the rate coefficients for ion transfer via major pathways and studying their alteration under various conditions

Transition of the system to the balanced state as displayed in the file RESP.txt.

<p>Transition of the system to the balanced state as displayed in the file RESP.txt.</p

Symbols and definitions.

<p>Symbols and definitions.</p

Observed and computed Li/Na discrimination coefficient <i>c</i>_<i>d</i> = ([Li]_i/ [Na]_i)·([Na]_o/[Li]_o) in U937 cells under the balanced state at different [Li]_o.

<p>Observed and computed Li/Na discrimination coefficient <i>c</i>_<i>d</i> = ([Li]_i/ [Na]_i)·([Na]_o/[Li]_o) in U937 cells under the balanced state at different [Li]_o.</p

Recovery of ion balance in U937 cells preloaded with Li⁺.

<p>(A) Observed changes in [Li]_i, [K]_i, [Na]_i after placing cells into Li⁺-free RPMI medium. Computed net fluxes in the model cells placed in a Li⁺-free medium without (B) or with (C and D) Na⁺, as well as without (B and C) or with (D) Li/Na countertransporter. The parameters used in the calculations: <i>kv</i> 1, <i>na</i> 2, <i>k</i> 73, <i>l</i> 96, <i>cl</i> 76, <i>alpha</i> 0, <i>beta</i> 0.039, <i>gamma</i> 1.5, <i>pna</i> 0.00349, <i>pk</i> 0.0229, <i>pl</i> 0.00349, <i>pcl</i> 0.00426, <i>inc</i> 3E-5, <i>ilc</i> 0, <i>ikc</i> = <i>inkcc</i> = <i>ilkcc</i> = 0, <i>hp</i> 400. (B) <i>na0</i> 0.01, <i>k0</i> 5.8, <i>cl0</i> 116, <i>l0</i> 0.01, <i>B0</i> 188.2; (C, D) <i>na0</i> 140, <i>k0</i> 5.8, <i>cl0</i> 116, <i>l0</i> 0.01, <i>B0</i> 48.2; <i>kp</i> is indicated on the graphs. The graphs on the right show the changes in membrane potential and water balance.</p

Symbols and definitions.

<p>Symbols and definitions.</p