It is certain that the membrane potential has something to do with the face that Na ions have a higher concentration outside the cell and K+ ions inside.
Starting from a condition in which both ions inside and outside the cell are equally concentrated, the active interference of the cell membrane soon shifts the balance.
A simple explanation of how this comes about is that of a sodium pump in the membrane, which continuously transports Na+ ions from inside to outside, and thus charges the membrane positively.
The K+ ions, according to this theory, passively follow the electrostatic force produced by this charge and pile up inside the cell.
Another hypothesis is that of a sodium-potassium pump in the membrane that continuously discharges Na+ ions from the cell while it brings in an equal quantity of K+ ions.
According to this theory, the symmetric movement of two positive ions indirectly generates the charge of the membrane, which results from the difficult mobilities of Na+ and K+ ions through the membrane.


(1) なぜ1つ目の解説(A simple explanation of ~の文)ではsodiumpumpと表記し2つ目の解説( Another hypothesis is ~の文)ではsodium-potassium pumpと表記しているんでしょうか。

(2) A simple explanation of と Another hypothesis is の文「is that of」と出てくるんですがこの「that」は同じ単語(explanation)を使うのを避けていると考えていいんでしょうか?

(3) A simple explanation of と Another hypothesis is の2つの解釈の違いとは何なのでしょうか?

A 回答 (1件)

(1) 一つ目の解説ではNaポンプが中から外へNaを移動させており、K+イオンは受動的に(Naの移動を補うように)外から中へ移動するだけのメカニズムなので、ポンプ作動の対象は<Naのみ>です。


(2) that = explanation, that = hypothesis です。is that of を省略して is a sodium pump, hypothesis is a sodium-potassium pump と書いても通じるでしょうが、is that of があることで文章の形を整えていると考えられます。

(3) 化学音痴ですが、文面上は2つのメカニズムには (1) に書いたような違いがあります。
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that = explanation, that = hypothesis だったんですか。

お礼日時:2009/05/26 10:59