NaCl transport by Madin Darby canine kidney cyst epithelial cells

NaCl transport by Madin Darby canine kidney (MDCK) cyst epithelial cells. The mechanism of NaCl transport across the epithelium of intact MDCK cysts grown in a collagen gel matrix was investigated. Double-barreled microelectrodes were used to measure basolateral membrane PD (Vb1), transepithelial PD (Vt), and intracellular (Cli) and intralumenal (Clcy) Cl- activities in cysts under different conditions. In a control Ringer's solution (RS), Cli (60 ± 1mM) and Clcy (107 ± 2mM) exceeded the values corresponding to electrochemical equilibrium across the basolateral membrane and epithelium, respectively. Cli was reduced by superfusing the cysts with a low Cl- RS (Cli, 20 ± 3mM), a low Na+ RS (Cli, 40 ± 4mM), or by adding amiloride to the control RS (Cli, 46 ± 1mM). Cli was unaffected by removal of either K+ or HCO3- from the RS or by adding furosemide or SITS to the control RS. Vb1 in the control RS was -50 ± 2mV and was affected only by removal from the RS of K+ (Vb1, -31 ± 3mV) or HCO3- (Vb1, -29 ± 4mV) or by the addition of SITS to the control RS (Vb1, -59 ± 5mV). Vt in control RS was -2 ± 0.2mV (lumen negative), and was increased by reducing bath Na+ (Vt, -37 ± 2mV) but not by reducing bath Cl-. These data indicate that Cl- is secreted in a basolateral to apical direction by the cyst epithelium. Basolateral Cl- transport probably occurs mainly by an electroneutral Cl-/HCO3- exchanger. Transepithelial Na+ transport seems to occur via a paracellular route which appears to be cation selective. These experiments also support the existence, in the basolateral membrane, of a Na+/K+ ATPase, a Na+/H+ exchanger, and possibly a Na+/HCO3-/ CO32- transporter.