title: Na+/H+ antiport activity and cell growth in cultured skin fibroblasts of IDDM patients with nephropathy.
abstract: IDDM patients with incipient and overt nephropathy have been found to exhibit an overactivity of RBC sodium-lithium countertransport. To explore the physiological relevance of this finding, we measured the activity of Na+/H+ antiport in serially passaged cultured skin fibroblasts from IDDM patients with and without nephropathy and from normal, nondiabetic control subjects. Na+/H+ antiport activity (measured as the rate of amiloride-sensitive Na+ influx at pHi = 6.4, extracellular pH = 8.0, and [Na+] = 1 mM) was elevated significantly in IDDM patients with nephropathy compared with IDDM patients without nephropathy and nondiabetic control subjects (13.35 +/- 3.8 vs. 8.54 +/- 2.0 vs. 7.33 +/- 2.3 nmol Na+.mg protein-1.min-1; P less than 0.006 and P less than 0.001, respectively). A kinetic analysis of Na+/H+ antiport activity showed that the raised activity in IDDM patients with nephropathy was caused by an increased Vmax for extracellular Na+. Km values were similar in the three groups. pH-stimulated amiloride-sensitive Na+ influx also was higher under baseline conditions and after serum stimulation in cells from IDDM patients with nephropathy. pHi values were significantly higher, both during active proliferation and after 10-min exposure to serum, in cells from IDDM patients with nephropathy, compared with IDDM patients without nephropathy and nondiabetic control subjects. Serum-stimulated incorporation of [3H]thymidine into DNA was greater in IDDM patients with nephropathy than in the other two groups (35.7 +/- 18.9- vs. 17.4 +/- 7.5- vs. 11.9 +/- 8.7-fold stimulation above baseline; P less than 0.01 for both.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Unit for Metabolic Medicine, United Medical School, Guy's Hospital, London, United Kingdom.
authors.forename: R
authors.initials: R
authors.lastname: Trevisan
authors.forename: L K
authors.initials: LK
authors.lastname: Li
authors.forename: J
authors.initials: J
authors.lastname: Messent
authors.forename: T
authors.initials: T
authors.lastname: Tariq
authors.forename: K
authors.initials: K
authors.lastname: Earle
authors.forename: J D
authors.initials: JD
authors.lastname: Walker
authors.forename: G
authors.initials: G
authors.lastname: Viberti
mesh_terms: D000328:Adult; D000584:Amiloride / Q000494:pharmacology; D000704:Analysis of Variance; D002352:Carrier Proteins / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism* / Q000473:pathology*; D003928:Diabetic Nephropathies / Q000378:metabolism* / Q000473:pathology*; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008094:Lithium / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012867:Skin / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D008094:Lithium; D012964:Sodium