Regulation of intracellular pH in rabbit cortical connecting tubule and cortical collecting duct

Abstract

Proton transport pathways in isolated superfused rabbit cortical connecting (CNT) and collecting tubules (CCD) were determined using the fluorescent pH-sensitive dye BCECF following acid or base load by exposure to NH 4Cl. Following removal of NH 4Cl which results in a rapid decline in pH i two mechanisms appear to be responsible for pH i recovery, a Na-independent NEM-sensitive H efflux with a slow activity, which was virtually absent in 30% of the segments tested and a second rapid Na-dependent H efflux. In CCD this latter pathway was shown to have an apparent K m for (Na +) e of 38.2 ± 0.4 mM (S.D., n = 7) and was sensitive to EIPA. Similar results were obtained with the CNT. With regard to the H pump in six out of ten CCD isoproterenol (200 nM) resulted in a 2-fold stimulation of H pump activity. These effects of isoprenaline were inhibited both by the non-specific β-adrenoceptor antagonist propranolol as well as by the specific b 1 antagonist metoprolol. Interestingly, these stimulatory effects of this β agonist, which is known to stimulate cAMP formation in rabbit CCD, were not reproduced by the addition of exogenous cAMP analogues db cAMP (0.1 mM), CPT cAMP (0.1 mM), 8 Br-cAMP (0.1 mM) or the addition of forskoline (0.3 mM). In conclusion, these data obtained in isolated rabbit CNT and CCT demonstrate the presence of an active Na-H exchange which is for the most part responsible for the recovery of pH i. It should be noted also that the contribution of the H pump to pH i regulation appears to be negligible in these segments.