SODIUM AND WATER TRANSPORT IN CORTICAL COLLECTING DUCT OF DAHL SALT-RESISTANT RAT

Studies were conducted to determine whether the cortical collecting du ct (CCD) of the Dahl salt-resistant rat (inbred Rapp strain; R/Jr) exh ibits the same responses to deoxycorticosterone (DOG; 2.5 mg as a depo t injection in vivo, 3-8 days before experimentation) and arginine vas opressin (AVP, 220 pM in vitro) as the Sprague-Dawley (SD) [L. Chen, S .K. Williams, and J. A. Schafer. Am. J. Physiol. 259 (Renal Fluid Elec trolyte Physiol. 28): F147-F156, 1990] and Dahl salt-sensitive (inbred Rapp strain, S/Jr) [C. T. Hawk and J. A. Schafer. Am. J. Physiol. 260 (Renal Fluid Electrolyte Physiol. 29): F471-F478, 1991] CCD. Qualitat ively, the R/Jr CCD responded as in the other two strains: AVP elevate d the osmotic water permeability (P-f, mu m/s) from 0 to similar to 1, 200; either AVP or DOC, when used alone, increased the lumen-to-bath N a-22(+) flux (J(l-->b), pmol.min(-1).mm(-1)) from the control range of 20-25 to similar to 40 and hyperpolarized the transepithelial voltage . AVP and DOC effects were synergistic, elevating J(l-->b) to 90 +/- 5 (mean +/- SE) with both hormones, but this value was significantly lo wer than observed previously in both the SD and the S/Jr CCD, 125 +/- 6 and 140 +/- 6, respectively. However, bath-to-lumen fluxes (J(b-->l) ) were also significantly lower than observed in the SD and S/Jr CCD. Because net fluxes (J(net)) in these experiments can be determined onl y as nonpaired differences between unidirectional fluxes, it is uncert ain whether J(net) values in the R/Jr CCD are significantly lower than in the SD or S/Jr CCD. Nevertheless, the lower unidirectional Na+ flu xes in the R/Jr CCD indicate that the transepithelial transport of thi s ion is different in the R/Jr than in the other two strains, a fact t hat may be associated with its resistance to the development of hypert ension when placed on a high-salt diet.