Water transport and intracellular pH regulation in Cortical Collecting Duct cells

CAPURRO CLAUDIA; RIVAROLA VALERIA; FORD PAULA; CHARA OSVALDO; PARISI MARIO

Buenos Aires, Argentina

Simposio; Satelite Symposium XIV International Biophysics Congress; 2002

The renal cortical collecting duct plays an important role in the regulation of water and electrolyte balance. Nevertheless, the mechanisms underlying these processes are not yet completely clear. We studied these mechanisms in a recently cloned epithelial cell line derived from the rat cortical collecting duct (RCCD,). Water transport studies showed that these cells, cultured on a permeable support, developed an "absorptive component" associated to Na+ and Cl- absorption and a "secretory component" associated to Cl- and HCO3 secretion. These water movements were observed in absence of native AQPs. On the other hand, while the hydrostatic permeability (Phidr) induced a mainly paracellular water transport, osmotic permeability (Posm) was dependent of active transport indicating that DP induces a predominant transcellular water flux. Moreover, the natriferic response to AVP, preserved in RCCD1 cells, was associated with a change in net water flux, but the hydro-osmotic response to AVP was completely lost. RCCD1 cells transfected with AQP2, as compared with wild type, showed no changes in Phidr while the Posm was significantly increased and the hydro-osmotic response to AVP was restituted. In many cell types, it is propose that acute osmotic shrinkage causes parallel activation of Na+/H+ (NHE) and Cl-/HCO3- (AE) exchangers, resulting in net uptake of NaCl and water that returns cell volume to its original valué. Our functional and molecular studies demonstrated the presence of NHE-1 and NHE-2 isoforms in RCCD1 cells. The obtained results strongly suggest that both isoforms are expressed in the basolateral membrane but they have differential roles: NHE-1 would be responsible of pHi recovery after an acid load and NHE-2 would be mainly involved in steady-state pHi and cell volume regulation. On the other hand, functional and molecular studies demonstrated the basolateral expression of AE2 isoform involved in steady-state pHi The expression of NHE and AE isoforms in RCCD1 cells allow us to study the involvement of these proteins in the response to an osmotic shock either in native cells or in cells expressing AQPs.