Cooperation between potassium channels and gap junctions: interaction between Kv1.1 channel and Pannexin 1

Abstract

The beta 3 subunit of voltage gated has been recently identified as a modulatory macromolecule of pannexin 1. Our interest has focused on the possible interaction between the alpha subunit of Kv1.1 channel and pannexin 1. Through voltage clamp studies we have analyzed the electrical activity of the single channels and their behavior when they were coexpressed. With our results we have demonstrated that pannexin 1 was less susceptible to its inhibitors, like probenecid and DTT, when it was coexpressed with Kv1.1 channel, on the contrary pannexin 1 did not seem to influence the activity of Kv1,1 channel. Through immunocytochemistry on HEK-hBK1 cells expressing in stable way Kv1.1 channel we have observed the colocalization of the two channels but through coimmunoprecipitation we proved the lack of a physical interaction between these proteins, therefore the interaction should be functional. Moreover previous studies has reported an involvement of pannexin 1 in apoptosis at elevated concentrations of extracellular potassium. So we wanted to estimate the cell death in presence and absence of pannexin 1 inhibitors, using like control SH-SY5Y cells, being a cell line that does not express Kv1.1 channel. With our results we have obtained a decreased in the cell death when HEK-hBK1 cells were treated with probenecid 1 mM in presence of KCl 140 mM suggesting that this behavior was the consequence of pannexin 1 inhibition, therefore in these conditions Kv1.1 channel did not influence in some way its activity; on the contrary the treatment with 10 mM DTT did not produce any benefical effects in HEK-hBK1 cells. These findings confirmed that Kv1,1 channel influenced the sensibility of pannexin 1 to its inhibitors only when redox potential was altered and then in presence of reducing agents, or when a depolarization of the membrane was induced like in oocytes, but this phenomenon didn t occur in other conditions. Probably this indirect interaction is mediated by other proteins, such as calmodulin and kinase proteins or by lipids of the membrane such as PIP2; it could represent a regulatory mechanism that replaces or enhances that exercised by beta 3 subunit on pannexin 1, in order to control the potassium buffering' and then the cell excitability and survival, both in pathological and physiological conditions.