Novel voltage-dependent Cl channels in striatal medium spiny neurons are unrelated to ClC-1 or other known Ca-induced Cl channel/transporter types.

Intracellular chloride (Cl) homeostasis is a critical regulator of neuronal excitability. Voltage-dependent neuronal Cl channels remain the least understood in terms of their role as a source of Cl entry controlling excitability. We have shown recently that striatal medium spiny neurons (MSNs) express a functional Cl conducting ClC-1-like channel with properties similar but not identical to native ClC-1 channels (Yarotskyy, V., Lark, A.R.S., Nass S.R., Hahn, Y.K., Marone, M.G., McQuiston, A.R., Knapp, P.E., Hauser, K.F. (2022) Am. J. Physiol. Cell. Physiol. 322 (2022) C395-C409). Using a myotonic SWR/J-Clcn1/J mouse model with a premature stop codon for the ClC-1 channel rendering it non-functional, we demonstrate that striatal MSNs isolated from wild type (wt) and homozygous mutant (adr) mouse embryos have identical voltage-dependent outwardly rectifying Cl currents. In contrast and as expected, homozygous adr skeletal muscle flexor digitorum brevis (FDB) fibers display nominal macroscopic Cl currents compared to heterozygous wild-type adr FDB fibers. Together, our findings demonstrate that the novel ClC-1-like channels in MSNs are unrelated to skeletal muscle-specific ClC-1 channels, and therefore represent a unique voltage-dependent neuronal Cl channel of unknown identity.