Regulation of intracellular pH in rabbit cortical connecting tubule and cortical collecting duct.
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 NH4Cl. Following removal of NH4Cl which results in a rapid decline in pHi two mechanisms appear to be responsible for pHi 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 Km 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 beta-adrenoceptor antagonist propranolol as well as by the specific b1 antagonist metoprolol. Interestingly, these stimulatory effects of this beta 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 forskolin (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 pHi. It should be noted also that the contribution of the H pump to pHi regulation appears to be negligible in these segments.
Dagher
G
G
Laboratoire de Physiologie Cellulaire, Collège de France, Paris.
Sauterey
C
C
D000136:Acid-Base Equilibrium / Q000187:drug effects / Q000502:physiology*; D000643:Ammonium Chloride / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002412:Cations / Q000378:metabolism*; D000242:Cyclic AMP / Q000031:analogs & derivatives; D005033:Ethylmaleimide / Q000494:pharmacology; D005452:Fluoresceins / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007545:Isoproterenol / Q000494:pharmacology; D007672:Kidney Cortex / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007684:Kidney Tubules / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D011522:Protons; D011817:Rabbits; D012964:Sodium / Q000378:metabolism
D002412:Cations; D005452:Fluoresceins; D011522:Protons; D000643:Ammonium Chloride; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium; D000242:Cyclic AMP; D008790:Metoprolol; D007545:Isoproterenol; D005033:Ethylmaleimide