LLC-PK1 cells serve as a widely used model for the renal proximal tubule. Until now, little has been found out about their membrane voltage (Vm) and ionic conductances (g). Several studies have shown changes in cell properties during differentiation and ageing. The aim of this study was to examine the relationship between Vm or g and the age of these cells. Therefore, we investigated single cells, subconfluent and confluent monolayers of LLC-PK1 cells aged 1-8 days with the slow-whole-cell patch-clamp technique. The Vm of all cells was -34 +/- 2 mV (n = 75) and the membrane conductance (gm) was 2.3 +/- 0.3 nS (n = 30). Vm in cells aged up to 2 days was -24 +/- 3 mV (n = 22) whereas Vm in cells aged 5-8 days was -50 +/- 3 mV (n = 15). An increase of extracellular K+ from 3.6 to 18.6 mmol/l led to a depolarization in all cells of 4 +/- 1 mV (n = 31) and an increase of gm by 17 +/- 13% (n = 15). Complete replacement of extracellular Na+ by N-methyl-D-glucamine (NMDG) led to a hyperpolarization of 19 +/- 2 mV (n = 38) and gm was lowered by 27 +/- 14% (n = 17). A reduction in extracellular Cl- from 147 to 32 mmol/l showed no significant effect on Vm (n = 16) or gm (n = 11).(ABSTRACT TRUNCATED AT 250 WORDS)