Fig. 7.
An extreme hypothesis with almost all of phosphoinositide metabolism occurring in Lo/raft domains of the PM. The Lo domain includes receptors, fast PtdIns(4,5)P2 breakdown, and fast restoration of PtdIns(4,5)P2 by local synthesis and/or by transfer or membrane fusion delivering precursors from intracellular membranes. The Ld domain has local PIP5K activity and exchanges DAG, PtdIns4P, and PtdIns(4,5)P2 surprisingly slowly with the Lo domain across the domain interface. PI, PtdIns; PIP, PtdIns4P; and PIP2, PtdIns(4,5)P2.