The effect of phenylalanine on the electrical properties of proximal tubule cells in the frog kidney.

The present study was designed to elucidate the effects of sodium-coupled transport on the electrical properties of proximal tubule cells in the isolated perfused frog kidney. Cable analysis techniques have been employed to determine the resistance of the luminal and peritubular cell membranes in parallel (Rm) and the apparent ratio of the luminal over the peritubular cell membrane resistance (VDR). Furthermore, the sensitivity of the potential difference across the peritubular cell membrane (PDpt) to 6-fold increases of peritubular potassium concentration (delta PDk) was taken as a measure of the relative potassium conductance of this membrane. In the absence of luminal phenylalanine, PDpt amounts to -60 +/- 1 mV (n = 90), Rm to 36 +/- 3 k omega cm (n = 22), VDR to 1.81 +/- 0.14 (n = 20), and delta PDk to 15.0 +/- 0.9 mV (n = 25). The application of 10 mmol/l phenylalanine replacing 10 mmol/l raffinose leads to a rapid (within 30 s) depolarisation of PDpt to 50 +/- 5% of its control value and to a delayed (within 12 min) recovery to 95 +/- 5% of control. The rapid depolarisation is associated with a decline of Rm and VDR, indicating a decrease mainly of the luminal cell membrane resistance. During recovery of PDpt there is a parallel increase of VDR and a further decline of Rm pointing to a decline of the basolateral cell membrane resistance. Delta PDk is decreased during rapid depolarisation but increases again during the recovery phase. Thus, phenylalanine initially decreases but then increases above control the apparent potassium conductance.(ABSTRACT TRUNCATED AT 250 WORDS)