The constitutively active mGluR1,5-Homer1a complex strongly activates BigK channels in cerebellar granule cells. Left, Under basal conditions, mGluR1 and Shank are cross-linked by Homer 3. Transient activation of mGluR1 by an mGluR1,5 agonist (DHPG) activates, in a reversible manner, BigK channels recorded in cell-attached patches (physiological recordings shown underneath). Right, Homer3 antisense or activity-induced Homer1a induction releases mGluR1 from cross-linking, and they become constitutively active. This leads to constitutive activation of BigK channels recorded in cell-attached patches (physiological recordings shown underneath). The BigK channels are recorded in cell-attached patches. Application of DHPG does not further activate these channels, whereas application of an mGluR1 inverse agonist (Bay 36-7620), but not a neutral antagonist (not shown), inhibits the constitutive activation of BigK channels. *The mGluR1,5 receptors are constitutively activated.