title: A network thermodynamic two-port element to represent the coupled flow of salt and current. Improved alternative for the equivalent circuit.
abstract: A two-port for coupled salt and current flow is created by using the network thermodynamic approach in the same manner as that for coupled solute and volume flow (Mikulecky et al., 1977b; Mikulecky, 1977). This electrochemical two-port has distinct advantages over the equivalent circuit representation and overcomes difficulties pointed out by Finkelstein and Mauro (1963). The electrochemical two-port is used to produce a schematic diagram of the coupled flows through a tissue. The network is superimposable on the tissue morphology and preserves the physical qualities of the flows and forces in each part of an organized structure (e.g., an epithelium). The topological properties are manipulated independently from the constitutive (flow-force) relations. The constitutive relations are chosen from a number of alternatives depending on the detail and rigor desired. With the topology and constitutive parameters specified, the steady-state behavior is simulated with a network simulation program. By using capacitance to represent the filling and depletion of compartments, as well as the traditional electrical capacitances, time-dependent behavior is also simulated. Nonlinear effects arising from the integration of equations describing local behavior (e.g., the Nernst-Planck equations) are dealt with explicitly. The network thermodynamic approach provides a simple, straightforward method for representing a system diagrammatically and then simulating the system's behavior from the diagram with a minimum of mathematical manipulation.
mesh_terms: D000818:Animals; D001692:Biological Transport; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008433:Mathematics; D008954:Models, Biological; D012492:Salts; D013816:Thermodynamics
chemical_list: D012492:Salts
references.citation: Biophys J. 1963 May;3(3):215-37
references.pmid: 19431324
references.citation: J Gen Physiol. 1959 Mar 20;42(4):847-63
references.pmid: 13631208
references.citation: J Gen Physiol. 1959 Mar 20;42(4):831-45
references.pmid: 13631207
references.citation: Am J Physiol. 1978 Sep;235(3):R121-9
references.pmid: 696850
references.citation: J Gen Physiol. 1977 May;69(5):571-604
references.pmid: 301179
references.citation: Comput Programs Biomed. 1978 Sep;8(3-4):171-9
references.pmid: 226327
references.citation: Prog Biophys Mol Biol. 1977;32(1):1-82
references.pmid: 343173
references.citation: Biophys J. 1979 Jan;25(1):87-105
references.pmid: 262387
references.citation: Comput Programs Biomed. 1978 Sep;8(3-4):180-95
references.pmid: 755597
references.citation: Am J Physiol. 1978 Dec;235(6):F638-48
references.pmid: 736148
references.citation: J Theor Biol. 1978 Aug 21;73(4):697-710
references.pmid: 703342
references.citation: Microvasc Res. 1978 Mar;15(2):207-20
references.pmid: 661612
references.citation: J Theor Biol. 1977 Dec 7;69(3):471-510
references.pmid: 607018
references.citation: J Theor Biol. 1977 Mar 21;65(2):215-29
references.pmid: 853747
references.citation: Q Rev Biophys. 1973 Feb;6(1):1-134
references.pmid: 4576440
references.citation: IEEE Trans Biomed Eng. 1972 Mar;19(2):101-7
references.pmid: 5012023
references.citation: Biophys Chem. 1976 May;4(3):229-36
references.pmid: 949524
references.citation: Comput Biol Med. 1976 Apr;6(2):133-48
references.pmid: 1269247