Investigation and characterization of splice variations of L-Type Ca2+ channel, Cav 1.3, in chick basilar papilla and rat cochlea hair cells: Iimplications in hearing

Abstract

L-type Cav1.3 voltage-gated calcium channels play important roles in insulin secretion, regulating pacemaking activities, mediating synaptic neurotransmission in hair cells and learning and memory. For some time, a puzzling question asked was about the lack of correlation between the behaviors of the Cav1.3 channels recorded in native hair cells and cloned Cav1.3 channels recorded in heterologous HEK 293 cells. The native Ca2+ currents flowing through Cav1.3 channels of cochlear hair cells inactivate only little (Zidanic and Fuchs 1995) while those through heterologously expressed Cav1.3 channels in HEK293 cells do so markedly (Xu and Lipscombe 2001). To understand how these Cav1.3 channels are adapted to such unique behavior, as an initial step, we transcript-scanned mRNA obtained from P9 (before onset of hearing) and P28 (after onset of hearing) rat cochlea to determine whether alternative splicing at the C-terminus of Cav1.3 gene may produce a hair cell splice variant that does not inactivate. We find that the alternate use of exon 41 acceptor sites generated a splice variant that lost the calmodulin-binding IQ motif in the C-terminus. Besides analyzing the splicing patterns at the C-terminus of the Cav1.3 gene, we have identified all alternative splicing combinations in the I-II loop region. The I-II loop region in Cav1.3i?!1 subunit is known to be the location where many patterns of splice variations can be found. Detailed analyses of the distribution of intracellular I-II loop region splice variants revealed tissue specific and developmental regulation. This study provides essential information of new alternatively spliced exons of Cav1.3 channels which may play diverse roles in the field of hearing sciences.