| Effects of insulin and IGF on growth and functional differentiation in primary cultured rabbit kidney proximal tubule cells - Effects of IGF-I on Na+ uptake - |
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Ho-jae Han1, Kwon-moo Park1, Jang-hern Lee2, IL-suk Yang2 |
1College of Veterinary Medicine, Hormone Research Center, Chonnam National University
2College of Veterinary Medicine, Seoul National University |
| 초대배양된 토끼 신장 근위세뇨관세포의 성장과 기능분화에 대한 insulin과 IGF의 효과 - Na+ uptake에 대한 IGF-I의 효과 - |
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한호재1, 박권무1, 이장헌2, 양일석2 |
1전남대학교 수의과대학, 호르몬연구센터
2서울대학교 수의과대학 수의생리학교실 |
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| Abstract |
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It has been suggested that ion transport systems are intimately involved in mediating the effects of growth regulatory factors on the growth of a number of different types of animal cells in vivo. The functional importance of the apical membrane $Na^+/H^+$ antiporter in the renal proximal tubule is evidenced by estimates that this transporter mediates the reabsorption of approximately one third of the filtered load of sodium and the bulk of the secretion of hydrogen ions. This study was designed to investigate the pathway utilized by IGF-I in regulating sodium transport in primary cultured renal proximal tubule cells. Results were as follows : 1. $Na^+$ was observed to accumulate in the primary cells as a function of time. Raising the concentration of extracellular NaCl induced an decrease in $Na^+$ uptake compared with control cells in a dose dependent manner. The rate of $Na^+$ uptake into the primary cells was about two times higher in the absence of NaCl($40.11{pm}1.76pmole;Na^+/mg;protein/min$) than in the presence of 140mM NaCl($17.82{pm}0.94pmole;Na^+/mg;protein/min$) at the 30 minute uptake. 2. $Na^+$ uptake was inhibited by IAA($1{ imes}10^{-4}M$) or valinomycin($5{ imes}10^{-6}M$) treatment($50.51{pm}4.04$ and $57.65{pm}2.27$ of that of control, respectively). $Na^+$ uptake by the primary proximal tubule cells was significantly increased by ouabain($5{ imes}10^{-5}M$) treatment($140.23{pm}3.37%$ of that of control). When actinomycin D($1{ imes}10^{-7}M$) or cycloheximide($4{ imes}10^{-5}M$) was applied, $Na^+$ uptake was decreased to $90.21{pm}2.39%$ or $89.64{pm}3.69%$ of control in IGF-I($1{ imes}10^{-5}M$) treated cells, respectively. 3. Extracellular cAMP decreased $Na^+$ uptake in a dose-dependent manner($10^{-8}-10^{-4}M$). IBMX($5{ imes}10^{-5}M$) also inhibited $Na^+$ uptake. Treatment of cells with pertussis toxin(50pg/ml) or cholera toxin($1{mu}g/ml$) inhibited $Na^+$ uptake. Extracellular PMA decreased $Na^+$ uptake in a dose-dependent manner(1-100ng/ml). 100 ng/ml PMA concentration significantly inhibited $Na^+$ uptake in IGF-I treated cells. However, staurosporine($1{ imes}10^{-7}M$) had no effect on $Na^+$ uptake. When PMA and staurosporine were added together, the inhibition of $Na^+$ uptake was not observed. In conclusion, sodium uptake in primary cultured rabbit renal proximal tubule cells was dependent on membrane potentials and intracellular energy levels. IGF-I stimulates sodium uptake through mechanisms that involve some degree of de novo protein and/or RNA synthesis, and cAMP and/or PKC pathway mediating the action mechanisms of IGF-I. |
| Key Words:
kidney, cell culture, IGF, sodium |
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