Role of NKCC1 in vasopressin‐induced cell swelling in renal collecting duct cell

Abstract

Vasopressin (AVP) increases both water permeability (Pf) and the cell height of isolated perfused renal collecting ducts. The mechanism of AVP-induced cell swelling remains unclear. We aimed to determine whether NKCC1 is necessary for the AVP-induced cell swelling. The presence of NKCC1 mRNA and protein in rat inner medullary collecting ducts (IMCD) were confirmed by RT-PCR and immunoblotting. For functional studies, IMCDs were microdissected and perfused in vitro. Cell height was measured using differential interference contrast microscopy. Pf was measured under an imposed 200 mOsm bath-to-lumen osmolality gradient (addition of NaCl) using fluorescein sulfonate as a volume marker. AVP increased cell height by 23% of the control condition, which can be inhibited by 100 uM bumetanide in the peritubular bath. This is consistent with the presence of bumetanide-sensitive transporter in the basolateral membrane of the IMCD cell. When IMCD was perfused under a 200 mOsm osmolality gradient by mannitol addition, AVP did not increase cell height, even though Pf increased from 74±12 to 371±33 μm/s, suggesting that AVP-induced cell swelling is dependent on a favorable NaCl gradient, and is not a necessary concomitant of increased lumen-to-bath osmotic water flux. Isolated perfused IMCDs dissected from NKCC1 null mice revealed that AVP did not increase the cell height. These results show that NKCC1 plays a key role in AVP-induced cell swelling in IMCD cell.