title: Parathyroid hormone and dibutyryl cAMP inhibit Na+/H+ exchange in renal brush border vesicles.
abstract: Parathyroid hormone (PTH) and cAMP inhibit sodium, water, and bicarbonate reabsorption in the proximal tubule. We wished to determine whether these agents directly inhibit proximal tubular Na+/H+ exchange. A suspension of rabbit proximal tubules was prepared by enzymatic digestion and Ficoll gradient centrifugation. Oxygen consumption at 37 degrees C was stable over 60 min, averaged 20 nmol X mg protein-1 X min-1, and was inhibited 60% by ouabain. Over 96% of cells excluded trypan blue. From this suspension, brush border membrane vesicles were isolated. The vesicles were enriched 12.7 times in alkaline phosphatase relative to a cortical homogenate and demonstrated pH gradient-stimulated, amiloride-sensitive Na+/H+ countertransport and sodium-phosphate and sodium-D-glucose cotransport. When the tubule suspension was exposed to PTH or dibutyryl cAMP, the activity of Na+/H+ countertransport in the resultant brush border vesicles was inhibited. Neither PTH nor dibutyryl cAMP affected the amiloride-insensitive component of sodium transport or sodium-phosphate or sodium-D-glucose cotransport. The effect of PTH on Na+/H+ counter-transport could not be explained by an alteration in fluidity of the brush border membrane. These experiments demonstrate that PTH and dibutyryl cAMP directly inhibit Na+/H+ countertransport in the brush border membrane of the rabbit proximal tubule.
authors.forename: A M
authors.initials: AM
authors.lastname: Kahn
authors.forename: G M
authors.initials: GM
authors.lastname: Dolson
authors.forename: M K
authors.initials: MK
authors.lastname: Hise
authors.forename: S C
authors.initials: SC
authors.lastname: Bennett
authors.forename: E J
authors.initials: EJ
authors.lastname: Weinman
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D005260:Female; D005947:Glucose / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D066298:In Vitro Techniques; D007474:Ion Exchange; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*
chemical_list: D010281:Parathyroid Hormone; D010710:Phosphates; D003994:Bucladesine; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium; D005947:Glucose