脳腫瘍細胞の電気生理学的諸性質とその診断への応用

ELECTROPHYSIOLOGICAL STUDY ON THE PROPERTIES OF BRAIN TUMOR CELLS AND ITS APPLICATION TO DIAGNOSIS

I．はじめに

　細胞の外壁を構成する細胞膜は，機能的には単に細胞の内と外とを境する働きだけではなく，必要な物質を外界からとりこみ，不必要な物質を外界に排出したり，また，細胞相互間の情報交換など細胞にとつてはきわめて重要な働きをしていると考えられる。さて，腫瘍化した細胞には，この細胞膜に機能的にも解剖学的にも何等かの変化がみられるはずである^23）。この細胞膜の変化は遺伝子の変化にもとつく二次的なものであろうが，細胞自体にとつては一次的な意義を有する重要な変化である。この細胞膜の変化に関する研究は，解剖学的にも生化学的にも生理学的にも幾多なされているが，われわれは従来この分野では余り用いられていない電気生理学的方法により，種々の脳腫瘍由来の培養細胞の膜の性質を比較検討した。その結果膜抵抗と腫瘍の種類および整流性とその腫瘍化との間に有意の関係のあることを見出したので報告したい。

　Intracellular microelectrode studies of brain tumorcells in tissue culture were performed. The cellsobtained by surgery were cultured by monolayermethod and fed with a nutrient medium consistingof 80% Eagle MEM and 20% fetal calf serum.Those cells cultured for 4 to 7 days were used forthe studies. Under the phase contrast microscope,a micromanupulator was used to control a fineglass micropipette filled with 3M KCl(5 ~ 15megohms)into cells. Total 702 cells were examined.

Results:

　1) Membrane potential

　Membrane potential recorded was -7 ~ -12 mVin general. No apparent difference was obtainedamong cell types and malignancy of brain tumors.

　2) Membrane resistance (depolarizing current10 nA)

　Astrocytoma I~II　　　1.39 MΩ

　Glioblastoma Multiforme　　　1.22 MΩ

　Oligodendroglioma　　　5.48 MΩ

　Ependymoma　　　1.20 MΩ

　Nomal cerebeller glial cell　　　1.46 MΩ

　Meninglioma　　　6.65 MΩ

　Neurinoma　　　2.65 MΩ

　Pituitary Adenoma　　　4.10 MΩ

　Oligodendroglioma has exceedingly high membrane resistance among the glial cells and neurinoma has also moderately high one. Oligodendroglia and Schwann cell act as nerve sheath in the central nervous system and peripheral nervous system respectively. Thus the value of membrane resistance differed among the cell types and functions, and it might be helpful for differentiating the cellular origin.

　3) Rectifying activity

　Rectifying activity was indicated by comparing the absolute values of potential differences at depolarizing current with those at hyperpolarizing current. The author defined rectifying index (R.I.) as indicated below.

　　R.I.＝｜V₊₁₀／V_-10｜

　V₊₁₀: potential difference at depolarizing current (10 nA)

　V_-10 : potential difference at hyperpolarizing current (-10 nA)

　Glioblastoma Multiforme　　　2.44

　Astrocytoma (grade I~II)　　　2.86

　Normal cerebellar glial cell　　　4.57

　It is suggested that the malignancy of the glioma cell may be assessed by this method, because the value of this index decreases as the malignancy increases.

　The electrophysiological studies on the properties of brain tumor cells should be very useful, not only for the basic study on the histiogenesis and malignant transformation of the tumor cells, but also for the clinical diagnosis of the nature of the cells and the evaluation of therapeutic effects of various drugs, irradiation or immunoactive substances.