But bitter substances block the channels that allow calcium into cells, which relaxes the tightened tissue.

但是苦味物质能够阻碍钙流入气道细胞，所以就能缓解拉紧的组织。

youdao

'Bitter' collocates with 'tears' but 'sour' does not.

bitter可与tears搭配，而sour则不可。

《牛津词典》

It is bitter, but it is good for you.

很苦，但对你有好处。

youdao

It was a bitter defeat. But it made the North recognize the need for a real army one trained and equipped for war.

VOA: special.2009.08.27

But both northern and southern extremists remained bitter.

VOA: special.2009.04.09

But bitter memories of repeated cycles of bust and boom, of hope and gloom, make it likely that politicians will choose mature compromise rather than risk plunging their country yet again into troubles like that.

ECONOMIST: Democracy day in Mexico

But a bitter row is bubbling about plans to rent out these peaceful properties.

BBC: Goring Lock

But his bitter and suspicious party colleagues are not giving him such leeway.

ECONOMIST: Israel's new government