The purpose of this study is to contribute to understanding the role of Na⁺-K⁺-ATPase and of ionic cotransporters in the regulation of cell volume, by employing a model that describes the rates of change of the intracellular concentrations of Na⁺, K⁺, and Cl, of the cell volume, and of the membrane potential. In most previous models of dynamic cellular phenomena, Na⁺-K⁺-ATPase is incorporated via phenomenological formulations; the enzyme is incorporated here via an explicit kinetic scheme. Another feature of the present model is the capability to perform short-term cell volume regulation mediated by cotransporters of KCl and NaCl. The model is employed to perform numerical simulations for a "typical" nonpolarized animal cell. Basically, the results are consistent with the view that the Na⁺ pump mainly plays a long-term role in the maintenance of the electrochemical gradients of Na⁺ and K⁺ and that short-term cell volume regulation is achieved via passive transport, exemplified in this case by the cotransport of KCl and NaCl.