The presence of HCO3- does not inhibit alpha-adrenergic increases in proximal tubular intracellular pH.
Hormonal stimulation of Na+/H+ exchange increased intracellular pH (pHi) in a dose-dependent manner in proximal tubules suspended in Krebs-Henseleit buffer (KHB) supplemented with 25 mM HCO3- and CO2 (KHB + HCO3). The maximum increase in pHi was approximately 45% of the response observed with segments suspended in bicarbonate-free buffer (KHB-HCO3) and the time required to achieve maximum pHi alterations was significantly increased (p less than 0.05) in the presence of KHB + HCO3 when compared to responses obtained in KHB - HCO3. Dose-response curves for agonist-induced pHi increases were shifted to the right by a factor of 10 for segments suspended in KHB + HCO3. Increases in pHi induced by agonists in KHB + HCO3 were effectively blocked by pretreatment with 10 microM ethylisopropyl amiloride but not with the Cl-/HCO3- inhibitor, DIDS (0.1 mM, 30 min). We conclude that stimulation of alpha-adrenergic receptors on proximal nephrons increased pHi due to activation Na+/H+ exchange and can be detected in the presence of HCO3- although the time course and maximum level of change differ significantly from those observed in a HCO3(-)-free buffer.
Gesek
F A
FA
Department of Internal Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond.
Schoolwerth
A C
AC
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D010281:Parathyroid Hormone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D001639:Bicarbonates; D010281:Parathyroid Hormone; D011942:Receptors, Adrenergic, alpha; D000804:Angiotensin II; D012964:Sodium; D013755:Tetradecanoylphorbol Acetate