Active and passive chloride transport by the rabbit cortical collecting duct

Dietary K intake has been shown to influence solute flux in the cortical collecting duct (CCD). We recently observed active Cl secretion by the CCD when rabbits were fed a K-rich diet. The present studies examined two different methods of K loading (KHCO3 or KCl) on net Cl flux (JNet Cl), active Cl flux (JA Cl), and passive Cl flux (JP Cl) by the rabbit CCD. These two methods of K loading were compared with a low-K diet (control or NaHCO3 diet) that had the same anion composition as the KHCO3 diet (Na for K substitution). In the low-K group there was neither significant net Cl transport nor active Cl secretion. Increasing dietary K content (KHCO3 group) resulted in significant net Cl secretion (JNet Cl = -26.3 +/- 9.3 pmol.mm-1.min-1). Moreover, K secretion was significantly greater (23.8 +/- 4.3 pmol.mm-1.min-1) and transepithelial voltage (VT) was more lumen negative (-14.8 +/- 5.9 mV) compared with the low-K group (P less than 0.05). Consequently, there was both significant passive Cl absorption and significant active Cl secretion. In the KCl group there was significant net Cl absorption (JNet Cl = 17.2 +/- 5.1 pmol.mm-1.min-1, P less than 0.05 vs. low-K diet). However, Na absorption significantly exceeded JNet Cl (JNet Na = 42.0 +/- 7.2 pmol.mm-1.min-1, P less than 0.01), and this group also exhibited the most lumen-negative voltage (VT = -35.4 +/- 5.4 mV).(ABSTRACT TRUNCATED AT 250 WORDS)