Vasopressin regulates water flow in a rat cortical collecting duct cell line not containing known aquaporins

Transepithelial water movements and arginine-vasopressin (AVP)-associated ones were studied in a renal cell line established from a rat cortical collecting duct (RCCD1). Transepithelial net water fluxes (J(W)) were recorded every minute in RCCD1 monolayers cultured on permeable supports. Spontaneous net water secretion was observed, which was inhibited by serosal bumetanide (10(-5) M), apical glibenclamide (10(-4) M) and apical BaCl2 (5 x 10(-3) M). RT-PCR, RNAse protection and/or immunoblotting experiments demonstrated that known renal aquaporins (AQP1, AQP2, AQP3, AQP4, AQP6 and AQP7) were not expressed in RCCD1 cells. AVP stimulates cAMP production and sodium reabsorption in RCCD1 cells. We have now observed that AVP significantly reduces the spontaneous water secretory flux. The amiloride-sensitive AVP-induced increase in short-circuit current (I-sc) was paralleled by a simultaneous modification of the observed J(W): both responses had similar time courses and half-times (about 4 min). On the other hand, AVP did not modify the osmotically driven J(W) induced by serosal hypertonicity. We can conclude that: (i) transepithelial J(W) occurs in RCCD1 cells in the absence of known renal aquaporins; (ii) the "water secretory component" observed could be linked to Cl- and K+ secretion; (iii) the natriferic response to AVP, preserved in RCCD1 cells, was associated with a change in net water flux, which was even observed in absence of AQP2, AQP3 or AQP4 and (iv) the hydro-osmotic response to AVP was completely lost.