Molecular evidence suggests that store-operated and receptor-operated
channels may be formed from proteins belonging to the same family,
being the mammalian homologues of the transient receptor potential
(TRP) channels.
Less clear whether they form the channels in native smooth muscle
One putative model is that TRPC proteins may fall into two classes;
one responsive to receptor activation but not store depletion and the
other responsive to store depletion.
McFadzean and Gibson  Br J Pharm 135: 1-13