Characterization of ST14A Cells for Studying Modulation of Voltage-Gated Calcium Channels

Abstract

In medium spiny neurons (MSNs) of the striatum, dopamine D2 receptors (D2Rs) specifically inhibit the Cav1.3 subtype of L-type Ca2+ channels (LTCs). MSNs are heterogeneous in their expression of dopamine receptors making the study of D2R pathways difficult in primary neurons. Here, we employed the ST14A cell line, derived from embryonic striatum and characterized to have properties of MSNs, to study Cav1.3 current and its modulation by neurotransmitters. Round, undifferentiated ST14A cells exhibited little to no endogenous Ca2+ current while differentiated ST14A cells expressed endogenous Ca2+ current. Transfection with LTC subunits produced functional Cav1.3 current from round cells, providing a homogeneous model system compared to native MSNs for studying D2R pathways. However, neither endogenous nor recombinant Cav1.3 current was modulated by the D2R agonist quinpirole. We confirmed D2R expression in ST14A cells and also detected D1Rs, D4Rs, D5Rs, Gq, calcineurin and phospholipase A2 using RT-PCR and/or Western blot analysis. Phospholipase C beta-1 (PLCbeta-1) expression was not detected by Western blot analysis which may account for the lack of LTC modulation by D2Rs. These findings raise caution about the assumption that the presence of G-protein coupled receptors in cell lines indicates the presence of complete signaling cascades. However, exogenous arachidonic acid inhibited recombinant Cav1.3 current indicating that channels expressed in ST14A cells are capable of modulation since they respond to a known signaling molecule downstream of D2Rs. Thus, ST14A cells provide a MSN-like cell line for studying channel modulation and signaling pathways that do not involve activation of PLCbeta-1.