Electrophysiology and ultrastructure of cultured human proximal tubule cells

The present study was undertaken to determine if cultures of human proximal tubule cells would retain in vivo properties inherent to this segment in the intact nephron. Ussing chamber studies demonstrated that these cultured cells generated transepithelial potential differences of approximately -2.0 mV and resistances of 0.310 K omega.cm2, supporting the concept that the proximal tubule is a "leaky" epithelium. The electrical properties did not change when the cells were exposed to amiloride (10(-4) M), but did respond to acetazolamide (10(-4) M), consistent with responses known to occur in proximal tubules. Ultrastructural analysis of these cells demonstrated features indicative of proximal tubule cells. When grown on permeable supports, where apical and basolateral growth medium compartments were maintained separate from each other, the cells were noted to undergo increased differentiation with morphological evidence of cell polarity. Freeze fracture analysis demonstrated well-formed tight junction strands and segregation of unique numbers of intramembranous particles in apical, lateral, and basal membranes. The replicas also demonstrated the presence of aggregates though to represent gap junctions, structures which occur exclusively in the proximal segment of the human nephron. These observations provide evidence that this human cell culture model originates from the human proximal tubule and retains, in culture, many of the properties associated with proximal tubule cell function and structure in vivo.