Do Pulmonary Ionocytes Absorb Chloride or Secrete Chloride?

Pulmonary ionocytes express high levels of cystic fibrosis transmembrane conductance regulator (CFTR) channels. When studied using the short-circuit current technique, ionocytes produce CFTR-dependent short-circuit currents consistent with Cl - secretion. However, when studied without a voltage-clamp, data indicate that ionocytes absorb Cl - . In this review, we resolve these seemingly conflicting findings by considering the different transepithelial voltages and resultant movement of Cl - during short-circuit and physiological open-circuit conditions. This analysis indicates that behavior under short-circuit conditions cannot be directly extrapolated to infer behavior under physiologic conditions. Finally, we discuss the potential role for basolateral Cl - channels in controlling absorption and secretion in ionocytes.