BK and CaV Channel Interactions in the Plasma Membrane

Abstract

Activation of the human voltage- and Ca2+-gated (BK, Slo1) K+ channel is triggered by both depolarization and increases in intracellular Ca2+ concentration. BK channels and different types of voltage gated (CaV) channels associate in the cell membrane such that Ca2+ entering via CaV channels activates BK channels. Protein co-localization and distribution at the plasma membrane level are typically addressed by fluorescence microscopy. We seek to gain insight into the relative proximity and positioning of BK channels and different types of CaV channels (CaV1.2 or CaV2.2) in the membrane by fitting to a mathematical model ionic current recordings obtained from Xenopus oocytes co-expressing BK and CaV channels. Prior to voltage clamp, the oocytes were injected with known concentrations of EGTA or BAPTA. Using the cut-open oocyte voltage-clamp technique, oocytes were subjected to a protocol consisting of two 80 mV pulses, separated by a −70 mV or 0 mV intermediate pulse of variable duration. The magnitude of the BK channel currents, during the second 80 mV pulse, depended on the amplitude and duration of Ca2+ entry during the intermediate pulse, as well as intracellular Ca2+ buffering conditions. Under the same experimental conditions, CaV2.2 channels activated BK channels more efficiently than CaV1.2 types, as suggested by the longer-lasting potentiation of the BK current when CaV2.2 and BK channels were co-expressed. We are interpreting the degree of physical association in view of a mathematical model that computes the activation of CaV and BK channels, as well as intracellular Ca2+ dynamics, and allows for varying density and relative distance between these channels. This model may be useful for predicting the relative distribution of CaV and BK channels in native cells.