Changes of LDH Subunit Combinations Induced by Tetrodotoxin

Tetrodotoxin에 의하여 유발되는 LDH 하부단위체 조합의 변화

In an attempt to make a scrutiny into a mechanism for the formation of quaternary structure of LDH isozymes, male mice were intraperitoneally exposed to a wide range of tetrodotoxin concentration and the changes in relative percentage of the five isozymes were monitored by electrophoresis and subsequent densitometry. The observations that a conspicuous increase of the $H_4$ isozyme was demonstrated in nearly all brain tissues, that the $M_4$ isozyme of skeletal muscle tissue was slightly increased while the $M_3H$ and $M_2H_2$ isozymes were decreased, that the M/H ratio was strikingly reduced in heart tissue and that assembly of $H_4$ isozyme was revealed in liver tissue although its rate was extremely low suggest that new intracellular ionic environment established by compulsory change in Donnan equilibrium could alter the LDH isozyme distribution. The reduction of assembly of $M_3H$ isozyme found in mouse tissues exposed to tetrodotoxin also seems to suggest that the subunit combination of 3M+H is very unfavorable in an intracellular environment deviated from its accustomed one. It was reaffirmed that there might occur TTX-insensitive sodium channels in plasma membrane.

LDH 동위효소의 4차구조 형성기작을 규명하기 위한 일환으로 웅성 흰쥐 복강내에 여러 가지 농도의 tetrodotoxin을 수차 주사한 후, 전기영동 및 densitometry에 의해 여러 조직내의 5가지 동위효소의 상대적 분포의 변화를 조사하였다. 뇌조직에서는 $H_4$ 동위효소가 현저히 증가하였고, 골격근조직에서 $M_4$ 동위 효소는 약간 증가한 반면 $M_3H$ 및 $M_2H_2$ 동위효소들은 감소되었으며, 심장조직에서는 M/H 비가 급격히 감소되었으며, 간조직에서는 소량의 $H_4$ 동위효소 형성이 나타났다. 이러한 결과들은 Donnan막 평형의 변화가 LDH 동위효소 분포의 변화를 초래할 수 있음을 시사한다. Tetrodotoxin에 노출된 흰쥐의 여러 조직내에서 $M_3H$ 동위효소 형성이 감소되는 사실로 미루어 고유한 세포질내 환경이 변화되면 3M+H 조합은 쉽게 이우러지지 않는 것으로 사료된다. 원형질 막의 어떤 sodium channel은 tetrodotoxin에 민감하지 않다는 사실이 재확인 되었다.