| Ionic currents elicited by the hypotonic solution in hamster eggs |
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Won-yeong Choi1, Yang-mi Kim2, Jae-hee Haan2, Il-oh Huh2, Choon-ok Park2, Seong-geun Hong2, Pan-dong Pyu3, Jong-shu Kim1 |
1College of Veterinary Medicine and Department of Physiology
2College of Medicine, Gyeongsang National University
3College of Veterinary Medicine Seoul National University |
| 저장성 용액에 노출된 햄스터 난자에 관찰되는 이온전류의 변화 |
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최원영1, 김양미2, 한재희2, 허일오2, 박춘옥2, 홍성근2, 류판동3, 김종수1 |
1경상대학교 수의과대학 약리학교실
2경상대학교 의과대학 생리학교실
3서울대학교 수의과대학 |
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| Abstract |
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Cell volume regulatory mechanisms are usually disclosed by exposure of cell to anisotonic media. If a cell is suddenly exposed to hypotonic media, it swells initially like an osmometer but within minutes regains its original cell volume. This behavior has been labelled as regulatory cell volume decrease(RVD). RVD is believed to result from the loss of permeable ions through the membrane. In this study, we examined hypotonically induced changes in the membrance currents involved in RVD by using whole cell voltage clamp technique in the unfertilized hamster egg. At -40mV of the holding potential, the stationary current was maintained in the hamster egg exposed to isotonic solution composed of, mainly, 115mM NaCl and 40mM mannitol. Hypotonic solution was prepared by removing mannitol. Therefore, the concentrations of $Na^+$ and $Cl^-$ in this hypotonic media were the same as those in the isotonic solution. Following 30 to 60 sec after applying the hypotonic media to the egg, the inward current was evoked. This inward current was eliminated by $100{mu}M$ 4-acetamido-4'-isothiocyanostil-bene-2,2'-disulfonic acid(SITS), an anion channel blocker, leaving the small outward current component. Further addition of 2mM $Ba^{2+}$, a broad $K^+$ channel blocker, completely abolished the small outward current left even in the presence of SITS during hypotonic stress. These results suggest that $K^+$ and $Cl^-$ move out of cells, resulting in RVD. To test the involvement of $Na^+$ in RVD, 20mM Na-isethionate was substituted for mannitol in isotonic media(135mM $Na^+$) and Na-isethionate (20mM) was freed the hypotonic solution. Only $Cl^-$ concentration in both isotonic and hypotonic media was kept constant at 115mM, whereas concentration of $Na^+$ was lowered in hypotonic solution to 115mM from 135mM in isotonic solution. Hypotonic medium induced the outward current in the egg equilibrated isotonically. This current was reduced by $100{mu}M$ SITS but was augmented by 2 mM $Ba^{2+}$. In terms of RVD, these results imply that $Cl^-$ efflux is coupled with $K^+$, maybe for electroneutrality during hypotonic stress and/or with $Na^+$ via unknown transport mechanism(s). From the overall results, the hypotonic stress facilitates the movement of $Cl^-$ and $K^+$ out of the hamster egg to regain cellular volume with electroneutrality. If there exist a difference in $[Na^+]_0$ between isotonic and hypotonic solution, another transport mechanism concerned with $Na^+$ may, at least partly, participate in regulatory volume decrease. |
| Key Words:
Cell volume regulatory mechanism, hypotonic media, $Cl^{-}$ efflux regulatory cell volume decrease(RVD) |
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