A Purkinje cell specific GoLoco domain protein, L7/Pcp-2, modulates receptor-mediated inhibition of Ca v 2.1 Ca 2+ channels in a dose-dependent manner

L7/Pcp-2 is a GoLoco domain protein encoded by a Purkinje cell dendritic mRNA. Although biochemical interactions of GoLoco proteins with Gα o and Gα i are well documented, little is known about effector function modulation resulting from these interactions. The P-type Ca 2+ channels might be physiological effectors of L7 because (1) they are the major voltage-dependent Ca 2+ channels (VDCC) that modulate Purkinje cell output and (2) they are regulated by G i/o proteins. As a first step towards validating this hypothesis and to further understand the possible physiological effect of L7 protein and its two isoforms, we have coexpressed Ca v 2.1 channels and κ-opioid receptors (KORs) with varying amounts of L7A or L7B in Xenopus oocytes and measured ionic currents by two-electrode voltage clamping. Without receptor activation L7 did not alter the Ca 2+ channel activity. With tonic and weak activation of the receptors, however, the Ca 2+ channels were inhibited by 40–50%. This inhibition was enhanced by low, but dampened by high, expression levels of L7A and L7B and differences were observed between the two isoforms. The enhancing effect of L7 was occluded by overexpression of Gβγ, whereas the disinhibition was antagonized by overexpression of Gα o. We propose that L7 differentially affects the Gα and Gβγ arms of receptor-induced G i/o signaling in a concentration-dependent manner, through which it increases the dynamic range of regulation of P/Q-type Ca 2+ channels by G i/o protein-coupled receptors. This provides a framework for designing further experiments to determine how dendritic local fluctuations in L7 protein levels might influence signal processing in Purkinje cells.