Insulin-like growth factor I stimulates apical sodium/hydrogen exchange in human proximal tubule cells.
To determine whether insulin-like growth factor I (IGF-I) stimulated apical sodium/hydrogen exchange (NHE), confluent primary human proximal tubule cells (PTC) were incubated for 48 h in serum-free media in the presence or absence of 100 ng/ml IGF-I. Cells incubated in IGF-I demonstrated significant increases in thymidine incorporation (181.2 +/- 30.3% of control values; n = 12, P = 0.01) and in resting intracellular pH (pHi) (7.52 +/- 0.08 vs. 7.30 +/- 0.06; n = 20, P < 0.05), as determined by 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein quantitative microspectrofluorometry. Following intracellular acid loading, ethylisopropylamiloride (EIPA)-inhibitable H+ efflux and 22Na+ influx after 1 min were both significantly enhanced in IGF-I-treated cells compared with controls (8.78 +/- 1.69 vs. 3.03 +/- 0.72 mM/min and 3.47 +/- 0.49 vs. 1.55 +/- 0.35 nmol x mg protein(-1) x min(-1), respectively). 22Na+ uptake studies in PTC grown on permeable supports demonstrated preferential stimulation of apical vs. basolateral NHE. The 50% inhibitory concentrations (IC50) in IGF-I-treated and control cells for EIPA (0.5 and 1.1 microM, respectively) and for HOE-694 (4.0 and 10.0 microM, respectively) were also consistent with predominant activation of apical, rather than basolateral, NHE activity. Kinetic analysis revealed an increase in maximal transport velocity (Vmax, 15.50 +/- 1.50 vs. 7.26 +/- 3.07 mM/min; n = 10, P < 0.05), without a significant change in antiporter affinity for extracellular Na+. Incubation of PTC with 100 ng/ml IGF-I produced an acute, reversible, and EIPA-inhibitable pHi increase of 0.05 +/- 0.01 pH units (n = 5, P < 0.05). The results suggest that IGF-I may contribute to the metachronous stimulation of apical NHE and PTC growth observed in many physiological and pathological conditions involving the human kidney.
Johnson
D W
DW
Department of Medicine, University of Sydney, Australia.
Brew
B K
BK
Poronnik
P
P
Cook
D I
DI
Field
M J
MJ
Györy
A Z
AZ
Pollock
C A
CA
D000328:Adult; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D004247:DNA / Q000096:biosynthesis; D005260:Female; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006146:Guanidines / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013450:Sulfones / Q000494:pharmacology; D013936:Thymidine / Q000378:metabolism
D016895:Culture Media, Serum-Free; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006146:Guanidines; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C057433:2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine; D007334:Insulin-Like Growth Factor I; D000584:Amiloride; D004247:DNA; D012964:Sodium; D013936:Thymidine; C039614:ethylisopropylamiloride