title: Effect of imidazolines on Na+ transport and intracellular pH in renal proximal tubule cells.
abstract: Recently, we characterized an imidazoline-guanidinium receptive site (IGRS) in the renal proximal tubule of rabbit kidney. Although recognized by a series of imidazoline and guanidinium alpha-2 adrenergic compounds, IGRS is insensitive to catecholamines and can be physically separated from alpha-2 adrenergic receptors after solubilization. In the present study, we investigated the effect of imidazoline derivatives on 22Na+ uptake and intracellular pH in isolated cells from rabbit renal proximal tubule. After 5 min of preincubation, idazoxan inhibited the total 22Na+ influx (-30%) in a dose-dependent manner, with a maximum effect at 10(-5) M. The effect of idazoxan was not competitive as shown by the decrease of the maximal velocity of 22Na+ entry (control: 3.80 +/- 0.42; idazoxan 10(-5) M: 3.23 +/- 0.33 nmol/30 s per mg protein, P less than 0.01). A series of imidazoline derivatives inhibited 22Na+ entry with an order of potency similar to that previously found for inhibition of [3H]idazoxan binding to IGRS (cirazoline greater than idazoxan greater than UK 14304 greater than rilmenidine much greater than cimetidine). The inhibition of 22Na+ uptake by these compounds does not appear to be related to interaction with alpha-adrenergic receptors since it was observed in the presence of saturating concentrations of the adrenergic antagonists rauwolscine (alpha-2) or prazosin (alpha-1). When tested on the regulation of intracellular pH by fluorimetric techniques, 10(-5) M cirazoline or idazoxan inhibited by 20% the velocity of the sodium-dependent H+ efflux in acidified cells (P less than 0.02). The concomitant inhibition of 22Na+ entry and of cell realkalinization suggests that imidazoline derivatives inhibit Na+/H(+)-exchanger. This effect could be mediated via the renal IGRS and intracellular second messengers that are not yet known.
authors.affiliation: Département de Biologie, Centre d'Etudes Nucléaires de Saclay, Gif-sur-Yvette, France.
authors.forename: M
authors.initials: M
authors.lastname: Bidet
authors.forename: P
authors.initials: P
authors.lastname: Poujeol
authors.forename: A
authors.initials: A
authors.lastname: Parini
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D000068438:Brimonidine Tartrate; D002927:Cimetidine / Q000494:pharmacology; D004146:Dioxanes / Q000494:pharmacology*; D004147:Dioxins / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D019329:Idazoxan; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D010080:Oxazoles / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011817:Rabbits; D000077769:Rilmenidine; D012964:Sodium / Q000378:metabolism*
chemical_list: D004146:Dioxanes; D004147:Dioxins; D007093:Imidazoles; D010080:Oxazoles; D011810:Quinoxalines; D000068438:Brimonidine Tartrate; D000584:Amiloride; D002927:Cimetidine; D012964:Sodium; D000077769:Rilmenidine; C014282:cirazoline; D019329:Idazoxan