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 -

초대배양된 토끼 신장 근위세뇨관세포의 성장과 기능분화에 대한 insulin과 IGF의 효과 - Na⁺ uptake에 대한 IGF-I의 효과 -

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($1{\times}10^{-4}M$) or valinomycin($5{\times}10^{-6}M$) 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($5{\times}10^{-5}M$) treatment($140.23{\pm}3.37%$ of that of control). When actinomycin D($1{\times}10^{-7}M$) or cycloheximide($4{\times}10^{-5}M$) was applied, $Na^+$ uptake was decreased to $90.21{\pm}2.39%$ or $89.64{\pm}3.69%$ of control in IGF-I($1{\times}10^{-5}M$) treated cells, respectively. 3. Extracellular cAMP decreased $Na^+$ uptake in a dose-dependent manner($10^{-8}-10^{-4}M$). IBMX($5{\times}10^{-5}M$) 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($1{\times}10^{-7}M$) 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.

이온운반계는 생체의 각기 다른 세포의 성장을 조절하는 성장조절인자들의 효과를 매개하는데 깊은 관련이 있는 것으로 보고되고 있다. 신장 근위세뇨관에서 솔변 연 $Na^+/H^+$ 상호운반계는 사구체에서 여과된 나트륨의 재흡수와 수소이온의 분비를 조절하는 중요한 기능을 수행한다. 이 연구는 초대배양된 신장 근위세뇨관세포의 나트륨 운반을 Insulin-like Growth Factor-I(IGF-I)이 어떤 경로를 통하여 조절하는지를 알아보고자 실시하였다. 결과는 아래와 같다. 1. 초대배양된 신장 근위세뇨관세포에서 $Na^+$ uptake는 시간의존적으로 증가되었으며, 30분동안 $Na^+$ uptake를 실시한 결과 세포외 NaCl 농도의존적으로 $Na^+$ uptake를 유의성있게 감소시켰다(대조군; $40.11{\pm}1.76$, 140mM군; $17.82{\pm}0.94pmole\;Na^+/mg\;protein/min$). 2. $Na^+$ uptake는 iodoacetic acid(IAA, $1{\times}10^{-4}M$) 또는 valinomycin($5{\times}10^{-6}M$)처리시 대조군에 비해 각각 $50.51{\pm}4.4%$와 $57.65{\pm}2.27%$ 억제되었으며, ouabain($5{\times}10^{-5}M$)을 처리한 경우는 $140.23{\pm}3.37%$ 증가되었다. IGF-I($1{\times}10^{-5}M$)으로 배양한 세포를 actinomycin D($1{\times}10^{-7}M$)와 cycloheximide($4{\times}10^{-5}M$)로 처리시 $Na^+$ uptake는 대조군에 비해 각각 $90.21{\pm}2.39%$와 $89.64{\pm}3.69%$로 감소되었다. 3. IGF-I으로 배양한 세포에서 세포외 cAMP는 농도의존적($10^{-8}-10^{-4}M$)으로 $Na^+$ uptake를 유의성있게 감소시켰고, 3-isobutyl-1-methyl-xanthine(IBMX, $5{\times}10^{-5}M$)도 억제시켰다. Pertussis toxin(PTX, 50pg/ml)이나 cholera toxin(CTX, $1{\mu}g/ml$)의 처리시에도 $Na^+$ uptake는 억제되었다. 세포외 phorbol 12-myristate 13 acetate(PMA) 또한 농도의존적(1-100ng/ml)으로 $Na^+$ uptake를 감소시켰다. 그러나 staurosporine($1{\times}10^{-7}M$)은 $Na^+$ uptake에 영향을 미치지 않았으며 PMA와 stauiosporine을 동시에 처리했을 때도 $Na^+$ uptake는 억제되지 않았다. 결론적으로 초대배양된 토끼 신장 근위세뇨관세포에서 $Na^+$ uptake는 막전위와 세포내 에너지 의존적이며 IGF-I은 부분적으로 단백질 및 RNA 합성을 통해서 그리고 세포내 cAMP나 PKC 경로를 통해서 $Na^+$ uptake를 조절하는 것으로 생각된다.