ROCs and SOCs: what's in a name?

There is currently a great deal of interest in the relative contributions of external and internally sequestered Ca(2+) in various physiological responses. However, this field is losing clarity due to inattentive use of terms. In particular, the terms "receptor-operated channels" and "store-operated channels" (ROCs and SOCs, respectively) are becoming ambiguous through over-use. In this paper, we will first consider basic principles of channel gating in order to set the stage for defining criteria which can be used to distinguish precisely between different channel-related functions. We will then focus on recurring examples of adventurous use of terminology, or of blurring of the distinctions between channel types, and propose solutions to this quandary.