It sounds like you've already narrowed your search to specific receptor subunits, in which case, it is the same wherever it is found. Functions can of course be very different from tissue to tissue. The only way to gather more information on that is to do a thorough literature search and find out about the known functions, tissue specificity in the body, signalling pathways in various tissues, etc.
In terms of a transcript resulting in many variants, you mean splice variants I suppose. Those would be described as different isoforms. For some proteins, many splice variants can be common and functional, for others, only a single form has been identified or is functional. Again, you just have to dig into the literature for each protein you're interested into find out what is known. It is always best to start with a current review article and work your way backward from there (and forward as necessary). This way, you'll know that if someone identified a new isoform of a receptor in say, 1998, any publications prior to that referring to the receptor are only referring to the previously known isoform.
Here's a good example; estrogen receptor is found in two known isoforms, the alpha and the beta form. However, the beta form was only discovered and confirmed approximately 10 years ago. All papers prior to that refer only to estrogen receptor. You then have to look at their methods to determine if their results apply to only estrogen receptor alpha (such as using an antibody that is now known to be specific for the alpha form), or for both forms (such as binding studies using radio-labeled estradiol that could bind to both receptor isoforms). There is also very recent debate that there is a third, membrane-bound form of estrogen receptor, but it has not been isolated yet, so there is much debate about whether that third form is actually an estrogen receptor or possibly something else, such as an ion channel activated by estrogen (there is evidence that supports both interpretations right now), so, it may be that in a few years, we'll need to read through a lot of that old literature keeping in mind that there could have been yet another mechanism of action of estradiol that had been overlooked and determine if those studies need to be interpreted differently in light of this new evidence.
As long as the isoform is identified, or the subunit specified, then you can be certain you are reading about the same thing in all tissues, but if the isoform or subunit in question is not specified, you'll need to pay close attention to the methods to see if it's the one relevant to what you're looking for.
