This paper explores the role and biophysical expression of the equivalent electrical circuit model as it applies to ionic conductances across the paracellular shunt, apical membrane, and basolateral membrane of the Ambystoma renal proximal tubule. Information about such conductances may be experimentally determined through transepithelial voltage and intracellular voltage measurements. The equivalent electrical circuit model has been applied extensively by investigators to define ion channels and transport mechanisms in the salamander proximal tubule. A comprehensive discussion of all known ionic conductance and transport pathways as well as pH-regulatory functions of contributory symports/antiports is examined in the Ambystoma proximal tubule. This paper explores renal physiological principles and serves as a companion to: Bock JF, Boulpaep EL: Bicarbonate transport mechanisms in the Ambystoma kidney proximal tubule: Transepithelial potential measurements.