Intermediate-conductance calcium-activated potassium channels participate in neurovascular coupling

BACKGROUND AND PURPOSE Controlling vascular tone involves K + efflux through endothelial cell small- and intermediate-conductance calcium-activated potassium channels (K Ca2.3 and K Ca3.1, respectively). We investigated the expression of these channels in astrocytes and the possibility that, by a similar mechanism, they might contribute to neurovascular coupling. EXPERIMENTAL APPROACH Transgenic mice expressing enhanced green fluorescent protein (eGFP) in astrocytes were used to assess K Ca2.3 and K Ca3.1 expression by immunohistochemistry and RT-PCR. K Ca currents in eGFP-positive astrocytes were determined in situ using whole-cell patch clamp electrophysiology. The contribution of K Ca3.1 to neurovascular coupling was investigated in pharmacological experiments using electrical field stimulation (EFS) to evoke parenchymal arteriole dilatation in FVB/NJ mouse brain slices and whisker stimulation to evoke changes in cerebral blood flow in vivo, measured by laser Doppler flowmetry. KEY RESULTS K Ca3.1 immunoreactivity was restricted to astrocyte processes and endfeet and RT-PCR confirmed astrocytic K Ca2.3 and K Ca3.1 mRNA expression. With 200 nM [Ca 2+] i, the K Ca2.1-2.3/K Ca3.1 opener NS309 increased whole-cell currents. CyPPA, a K Ca2.2/K Ca2.3 opener, was without effect. With 1 μM [Ca 2+] i, the K Ca3.1 inhibitor TRAM-34 reduced currents whereas apamin (K Ca2.1-2.3 blocker) had no effect. CyPPA also inhibited currents evoked by NS309 in HEK293 cells expressing K Ca3.1. EFS-evoked Fluo-4 fluorescence confirmed astrocyte endfoot recruitment into neurovascular coupling. TRAM-34 inhibited EFS-evoked arteriolar dilatation by 50% whereas charybdotoxin, a blocker of K Ca3.1 and the large-conductance K Ca channel, K Ca1.1, inhibited dilatation by 82%. TRAM-34 reduced the cortical hyperaemic response to whisker stimulation by 40%. CONCLUSION AND IMPLICATIONS Astrocytes express functional K Ca3.1 channels, and these contribute to neurovascular coupling. © 2011 The British Pharmacological Society.