This is a new concept, receptors don't have to be these molecules on cell surface, there can be receptors that exist in other places within the cell.

这是一个新概念,受体分子不一定只存在于细胞表面,它们也可以存在于细胞内其它地方

耶鲁公开课 - 生物医学工程探索课程节选