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¹ Department of Neuroscience, Brown University, Providence, RI 02912, USA

N-type Ca_V2.2 calcium channels localize to presynaptic nerve terminals of nociceptors where they control neurotransmitter release. Nociceptive neurons express a unique set of ion channels and receptors important for optimizing their role in transmission of noxious stimuli. Included among these is a structurally and functionally distinct N-type calcium channel splice isoform, Ca_V2.2e[37a], expressed in a subset of nociceptors and with limited expression in other parts of the nervous system. Ca_V2.2[e37a] arises from the mutually exclusive replacement of e37a for e37b in the C-terminus of Ca_V2.2 mRNA. N-type current densities in nociceptors that express a combination of Ca_V2.2e[37a] and Ca_V2.2e[37b] mRNAs are significantly larger compared to cells that express only Ca_V2.2e[37b]. Here we show that e37a supports increased expression of functional N-type channels and an increase in channel open time as compared to Ca_V2.2 channels that contain e37b. To understand how e37a affects N-type currents we compared macroscopic and single-channel ionic currents as well as gating currents in tsA201 cells expressing Ca_V2.2e[37a] and Ca_V2.2e[37b]. When activated, Ca_V2.2e[37a] channels remain open for longer and are expressed at higher density than Ca_V2.2e[37b] channels. These unique features of the Ca_V2.2e[37a] isoform combine to augment substantially the amount of calcium that enters cells in response to action potentials. Our studies of the e37a/e37b splice site reveal a multifunctional domain in the C-terminus of Ca_V2.2 that regulates the overall activity of N-type calcium channels in nociceptors.

(Received 9 June 2006; accepted after revision 14 July 2006; first published online 20 July 2006)
Corresponding author D. Lipscombe: Department of Neuroscience, Box 1953, Brown University, Providence, RI 02912, USA. Email: diane_lipscombe{at}brown.edu

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