NUMERICAL-SIMULATION OF EXCITATION-CONTRACTION COUPLING IN A LOCUS OFTHE SMALL-BOWEL

A mathematical model for the excitation-contraction coupling within a functional unit (locus) of the small bowel is proposed. The model assu mes that: the functional unit is an electromyogenic syncytium; its ele ctrical activity is defined by kinetics of L- and T-type Ca2+-channels , mixed Ca2+-dependent K+-channels, potential-sensitive K+-channels an d Cl--channels; the basic neural circuit, represented by the cholinerg ic and adrenergic neurones, provides a regulatory input to the functio nal unit via receptor-linked L-type Ca2+-channels; the smooth muscle s yncytium of the locus is a null-dimensional contractile system. With t he proposed model the dynamics of active force generation is determine d entirely by the concentration of cytosolic calcium. The model descri bes electrical processes of the propagation of excitation along the ne ural circuit, chemical mechanisms of nerve-pulse transmission at the s ynaptic zones and the dynamics of active force generation. Numerical s imulations have shown that it is capable of displaying different elect rical patterns and mechanical responses of the locus. The simulated ef fects of: tetrodotoxin, beta-bungarotoxin, salts of divalent cations, inhibitors of catechol-O-methyltransferase and neuronal uptake mechani sms, and changes in the concentration of external Ca2+ on the dynamics of force generation have been analysed. The results are in good quali tative and quantitative agreement with results of experiments conducte d on the visceral smooth muscle of the small bowel.