Competition for membrane phosphoinositides by different potassium channels?. (360G-Wellcome-082043_Z_07_Z)

Many ion channels require membrane phosphatidylinositol-4,5-bisphosphate (PIP2) to open. This work addresses a hypothesis that PIP2-activated ion channels might affect each other s activity through competition for available PIP2. This hypothesis follows from the applicants recent observations that, in sympathetic neurons, expressing the inwardly-rectifying potassium channel Kir2.1 (for which PIP2 has a high affinity) reduces currents carried by the endogenously-expressed lower-affinity M(Kv7) p otassium channel and sensitizes the M-channel to other forms of PIP2 sequestration. We aim to test this interaction further to determine whether this hypothesis can be substantiated or whether the interaction results from some other cause such as changes in M-channel expression. We shall measure the interaction using electrophysiological membrane current recording and will assess expression using both electrophysiolgical and immunocytochemical methods. We shall test whether the interaction is a dependent on the amount of Kir2.1 protein and (using mutants) on Kir2.1 affinity for PIP2, and how it is affected by changing the amount of available PIP2. If the hypothesis is substantiated, it will represent a new form of ion channel interaction, with important implications regarding the mobility of PIP2, ion channel localization, and receptor/PIP2-mediated signaling in neurons and other cells.