E. R. McNamara

Vasopressin-enhanced urea transport by rat inner medullary collecting duct cells in culture

Abstract. The distal inner medullary collecting duct (IMCD) is critical in the urinary concentrating process, in part because it is the site of vasopressin (AVP)‐regulated permeability to urea. The purpose of these experiments was to develop a cell culture model of the IMCD on permeable structure and to characterize the responsiveness to AVP. Rat IMCD cells were grown to confluence on collagen‐coated Millipore filters glued onto plastic rings. To assess the time required to achieve confluence, the transepithelial resistance was measured periodically and was found to be stable after 2 weeks, at a maximal value of 595 ± 22 ω cm2. In separate monolayers the effect of AVP on inulin and urea permeability was determined. While inulin permeability was unchanged after AVP, urea permeability increased from 6.0 ± 0–4 to peak values of 16.0 ± 3–8(10nM),23.1 ± 3–9(1 μM)and28 1 ± 4–9(10μM) X 10‐6cms‐1 (n= 24). In 10 other monolayers, after the addition of 1 mM 8‐Br‐cAMP, urea permeability increased from 5.1 ±0–3 to 8.1 ± 1–6 times 10‐6 cm s‐1 and, after 8‐Br‐cAMP +3‐isobutyl‐l‐methylxanthine, to 12.2 ± 0–7 times 10‐6 cms‐1. We conclude that rat IMCD cells grown in culture exhibit the characteristics of a ‘tight’ epithelium. Inulin and urea permeability are not different in the absence of AVP, consistent with high resistance junctional complexes. Furthermore, IMCD cells retain the capacity for AVP‐regulated urea permeability, a characteristic feature of this nephron segment in vivo.

Use of Lissamine Green for Micropuncture: A Comparison of Two Methods

Summary The effect of LG-SF dye on whole kidney function and proximal and distal tubular sodium and water reabsorption was studied in rats. In one group tubular samples were obtained immediately after injection of LG while in the other group collections were begun at least 30 min after the last dye injection. No differences between groups in tubular reabsorption of sodium, potassium, water, or whole kidney function were noted. We conclude that all aspects of renal function measured immediately after injection of LG-SF or 30-120 min later do not differ significantly. The authors greatly appreciate the secretarial help of Mrs. Mary Shea. These studies were supported by National Institutes of Health Grants HL 17458 and HL 18318.