Basolateral K+ conductance in principal cells of rat CCD

Basolateral K+ conductance in principal cells of rat CCD. Am J Physiol Renal Physiol 288: 17493-17504, 2005. First published November 16, 2004; doi:10.1152/ajprenal.00301.2004.Whole cell K current was measured by forming seats on the luminal membrane of principal cells in split-open rat cortical collecting ducts. The mean inward, Ba2+-sensitive conductance, with 40 mM extracellular K+, was 76 +/- 12 and 141 +/- 22 nS/cell for animals on control and high-K+ diets, respectively. The apical contribution to this was estimated to be 3 and 16 nS/cell on control and high-K+ diets, respectively. To isolate the basolateral component of whole cell current, we blocked ROMK channels with either tertiapin-Q or intracellular acidification to pH 6.6. The current was weakly inward rectifying when bath K+ was greater than or equal to 40 mM but became more strongly rectified when bath K+ was lowered into the physiological range. Including 1 mM spermine in the pipette moderately increased rectification, but most of the outward current remained. The K+ current did not require intracellular Ca2+ and was not inhibited by 3 mM ATP in,the pipette. The negative log of the acidic dissociation constant (pK(a)) was similar to6.5. Block by extracellular Ba2+ was voltage dependent with apparent K-i at -40 and -80 mV of -160 and -80 muM, respectively. The conductance was TEA insensitive. Substitution of Rb+ or NH+ for K+ led to permeability ratios of 0.65 +/- 0.07 and 4 0.15 +/- 0.02 and inward conductance ratios of 0.17 +/- 0.03 and 0.57 +/- 0.09, respectively. Analysis of Ba2+-induced noise, with 40 mm extracellular K+, yielded single-channel currents of 0.39 +/- 0.04 and -0.28 +/- 0.04 pA at voltages of 0 and -40 mV, respectively, and a single-channel conductance of 17 +/- 1 pS.