Genetic, Cellular, and Functional Evidence for Ca 2+ Inflow through Ca v 1.2 and Ca v 1.3 Channels in Murine Spiral Ganglion Neurons

• Published in: The Journal of neuroscience 2014-05, Vol.34 (21), p.7383-7393
• Main Authors: Lv, Ping, Kim, Hyo Jeong, Lee, Jeong-Han, Sihn, Choong-Ryoul, Fathabad Gharaie, Somayeh, Mousavi-Nik, Atefeh, Wang, Wenying, Wang, Hong-Gang, Gratton, Michael Anne, Doyle, Karen J., Zhang, Xiao-Dong, Chiamvimonvat, Nipavan, Yamoah, Ebenezer N.
• Format: Article
• Language: English
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.5416-13.2014

Spiral ganglion neurons (SGNs) of the eighth nerve serve as the bridge between hair cells and the cochlear nucleus. Hair cells use Ca v 1.3 as the primary channel for Ca 2+ inflow to mediate transmitter release. In contrast, SGNs are equipped with multiple Ca 2+ channels to mediate Ca 2+ -dependent functions. We examined directly the role of Ca v 1.3 channels in SGNs using Ca v 1.3-deficient mice ( Ca v 1.3 −/− ). We revealed a surprising finding that SGNs functionally express the cardiac-specific Ca v 1.2, as well as neuronal Ca v 1.3 channels. We show that evoked action potentials recorded from SGNs show a significant decrease in the frequency of firing in Ca v 1.3 −/− mice compared with wild-type ( Ca v 1.3 +/+ ) littermates. Although Ca v 1.3 is the designated L-type channel in neurons, whole-cell currents recorded in isolated SGNs from Ca v 1.3 −/− mice showed a surprising remnant current with sensitivity toward the dihydropyridine (DHP) agonist and antagonist, and a depolarization shift in the voltage-dependent activation compared with that in the Ca v 1.3 +/+ mice. Indeed, direct measurement of the elementary properties of Ca 2+ channels, in Ca v 1.3 +/+ neurons, confirmed the existence of two DHP-sensitive single-channel currents, with distinct open probabilities and conductances. We demonstrate that the DHP-sensitive current in Ca v 1.3 −/− mice is derived from Ca v 1.2 channel activity, providing for the first time, to our knowledge, functional data for the expression of Ca v 1.2 currents in neurons. Finally, using shRNA gene knockdown methodology, and histological analyses of SGNs from Ca v 1.2 +/− and Ca v 1.3 +/− mice, we were able to establish the differential roles of Ca v 1.2 and Ca v 1.3 in SGNs.