Ion transport in 'tight' epithelial monolayers of MDCK cells

Cultured monolayers of MDCK cells grown upon filter supports display many features of in vivo epithelia. Previously reported values of transmonolayer resistance of 100 omega cm-2 (Misfeldt, Hamamoto & Pitelka, 1976; Cereijido, Robbins, Dolan, Rotunno & Sabatini, 1978) indicate a leaky epithelium. This paper describes the properties of a strain of MDCK cells which displays entirely different electrophysiological properties. The results show that (i) the mean transmonolayer resistance is 4.16 k omega cm-2, (ii) transmonolayer ion transport is of small magnitude since the mean spontaneous open circuit PD is only 2.17 mV basal surface positive and isotopic Na and Cl flux measurements fail to demonstrate a significant net flux, (iii) the action of ouabain, amiloride and ion substitutions are consistent with transmonolayer net Na movement being largely responsible for the spontaneous PD, and (iv) asymmetry in the localization of the Na-K ATPase is evident on the basis of 3H-ouabain binding to cell monolayer.