The expression patterns of plasma membrane transporters that specify the epithelial cell type are acquired with ontogeny. To study this process during metanephrogenic mesenchyme-to-epithelium transition, branching ureteric buds with their adjacent mesenchymal blastema (mouse embryonic day E14) were dissected and explanted on a collagen matrix. In culture, induced mesenchymal cells condensed, aggregated, and converted to the comma- and S-shaped body. During in vitro condensation and aggregation, transcription factor Pax-2 protein was downregulated while the epithelial markers E-cadherin and beta-catenin proteins were upregulated. In addition, Wilms' tumor suppressor protein WT-1 was detectable upon condensation and downregulated in the S stage, where expression persisted in the long arm of the S. Patch-clamp, whole cell conductance (G, in nS/10 pF) of pre-epithelial condensed mesenchymal cells (n = 7) was compared with that of tubular proximal S-shaped-body epithelium (n = 6). Both stages expressed E-cadherin and WT-1 mRNA, as demonstrated by single-cell RT-PCR, testifying further to the epithelial as well as the nephrogenic commitment of the recorded cells. Mesenchymal cells exhibited whole cell currents (G = 6.7 +/- 1.3) with reversal potentials (V(rev), in mV) near equilibrium potential for Cl(-) (E(Cl)) (V(rev) = -40 +/- 7) suggestive of a high fractional Cl(-) conductance. Currents of the S-shaped-body cells (G = 4.0 +/- 1.1), in sharp contrast, had a V(rev) at E(K) (V(rev) = -82 +/- 6) indicating a high fractional K(+) conductance. Further, analysis of K(+)-selective whole cell tail currents and single-channel recording revealed a change in K(+) channel expression. Also, Kir6.1 K(+) channel mRNA and protein were downregulated between both stages, whereas K(v)LQT K(+) channel mRNA was abundant throughout. In conclusion, metanephrogenic mesenchyme-to-epithelium transition is accompanied by a profound reorganization of plasma membrane ion channel conductance.