OSR1 and SPAK Sensitivity of Large-Conductance Ca2+ Activated K+ Channel

Abstract

Background/Aims: The oxidative stress-responsive kinase 1 (OSR1) and the serine/threonine kinases SPAK (SPS1-related proline/alanine-rich kinase) are under the control of WNK (with-no-K [Lys]) kinases. OSR1 and SPAK participate in diverse functions including cell volume regulation and neuronal excitability. Cell volume and neuronal excitation are further modified by the large conductance Ca²⁺-activated K⁺ channels (maxi K⁺ channel or BK channels). An influence of OSR1 and/or SPAK on BK channel activity has, however, never been shown. The present study thus explored whether OSR1 and/or SPAK modify the activity of BK channels. Methods: cRNA encoding the Ca²⁺ insensitive BK channel mutant BK^{M513I+Δ899-903} was injected into Xenopus laevis oocytes without or with additional injection of cRNA encoding wild-type OSR1 or wild-type SPAK, constitutively active ^T185EOSR1, catalytically inactive ^D164AOSR1, constitutively active ^T233ESPAK or catalytically inactive ^D212ASPAK. K⁺ channel activity was measured utilizing dual electrode voltage clamp. Results: BK channel activity in BK^{M513I+Δ899-903} expressing oocytes was significantly decreased by co-expression of OSR1 or SPAK. The effect of wild-type OSR1/SPAK was mimicked by ^T185EOSR1 and ^T233ESPAK, but not by ^D164AOSR1 or ^D212ASPAK. Conclusions: OSR1 and SPAK suppress BK channels, an effect possibly contributing to cell volume regulation and neuroexcitability.