Properties of single K+ channels in the basolateral membrane of rabbit proximal straight tubules.

The basolateral membrane of rabbit straight proximal tubules, which were cannulated and perfused on one side, was investigated with the patch clamp technique. Properties of inward and outward directed single K+ channel currents were studied in cell-attached and inside-out oriented cell-excised membrane patches. In cell-attached patches with NaCl Ringer solution both in pipette and bath, outward K+ currents could be detected after depolarization of the membrane patch by about 20-30 mV. The current-voltage (i/V) relationship could be fitted by the Goldman-Hodgkin-Katz (GHK) current equation, with the assumption that these channels were mainly permeable for K+ ions. A permeability coefficient PK of (0.17 +/- 0.04).10(-12) cm3/s was obtained, the single channel slope conductance at infinite positive potential g(V infinity) was 50 +/- 12 pS and the single channel conductance at the membrane resting potential g(Vbl) was 12 +/- 3 pS (n = 4). In cell-excised patches, with NaCl in the pipette and KCl in the bath, the data could also be fitted to the GHK equation and yielded PK = (0.1 +/- 0.01).10(-12) cm3/s, g(V infinity) = 40 +/- 4 pS and g(Vbl) = 7 +/- 1 pS (n = 8). In cell-attached patches with KCl in the pipette and NaCl in the bath, inward K+ channels occurred at clamp potentials less than or equal to 60 mV, whereas outward K+ channel current was detected at more positive voltages. The current-voltage curves showed slight inward rectification.(ABSTRACT TRUNCATED AT 250 WORDS)