Effects of glutaraldehyde fixation on renal tubular function. I. Preservation of vasopressin-stimulated water and urea pathways in rat papillary collecting duct.

Using the in vitro microperfusion technique on isolated rat papillary collecting duct (PCD), we examined whether the glutaraldehyde-fixation method can be also applied to the mammalian collecting duct for preservation of the vasopressin-stimulated water and urea transport. Arginine vasopressin (AVP) at 10(-9) mol/l increased diffusional water permeability (Pdw) from 101.9 +/- 10.76 to 283.3 +/- 16.67 X 10(-7) cm2 s-1 (n = 8, P less than 0.01) and urea permeability (Purea) from 30.3 +/- 2.24 to 83.5 +/- 7.80 X 10(-7) cm2 s-1 (n = 8, P less than 0.01). Both parameters remained elevated after fixation with 0.1 mol/l glutaraldehyde even in the absence of AVP, with the values being 265.0 +/- 14.47 and 74.5 +/- 7.15 X 10(-7) cm2 s-1, respectively. Glutaraldehyde fixation did not affect the basal levels of Pdw or Purea. Phloretin at 2.5 X 10(-4) mol/l decreased glutaraldehyde-fixed AVP-stimulated Purea from 79.0 +/- 7.96 to 29.7 +/- 3.66 X 10(-7) cm2 s-1 (n = 4, P less than 0.01) and from 73.2 +/- 7.05 to 38.7 +/- 3.53 X 10(-7) cm2 s-1 (n = 4, P less than 0.01) when the drug was added to the lumen or to the bath, respectively. Phloretin also decreased glutaraldehyde-fixed non-stimulated Purea by 25-40%. However, this drug did not affect glutaraldehyde-fixed Pdw. These findings indicate that the glutaraldehyde fixation method can be applied to mammalian collecting tubules for studying vasopressin stimulated Pdw and Purea. Purea fixed by glutaraldehyde is functionally flexible and may be distinct from the water pathway.