Homer regulation of native plasma membrane calcium channels in A431 cells.

Homers are adapter proteins that play a significant role in the organization of calcium signaling protein complexes. Previous functional studies linked Homer proteins to calcium influx in nonexcitable cells. These studies utilized calcium imaging or whole-cell current recordings. Because of limited resolution of these methods, an identity of Homer-modulated ion channels remained unclear. There are several types of plasma membrane calcium influx channels in A431 cells. In the present study, we demonstrated that Homer dissociation resulted in specific activation of I(min) channels but not of I(max) channels in inside-out patches taken from A431 cells. In contrast, inositol 1,4,5-trisphosphate activated both I(min) and I(max) channels in inside-out patches. Short (1a) and long (1c) forms of Homer had different effects on I(min) channel activity. Homer 1a but not Homer 1c activated I(min) in the patches. This study indicates that I(min) channels are specifically regulated by Homer proteins in A431 cells.