New isoform of the neuronal Ca²⁺ channel α1E subunit in islets of Langerhans and kidney

Abstract

The expression of Ca 2ϩ channel A1E isoforms has been analyzed in different cell lines, embryoid bodies and tissues. The comparison of the different cloned A1E cDNA sequences led to the prediction of A1E splice variants. Transcripts of two cloned A1E isoforms, which are discriminated by a carboxy terminal 129-bp sequence, have been detected in different cell lines and tissues. Transcripts of the shorter A1E isoform have been assigned to the rat cerebrum and to neuron-like cells from in vitro, differentiated embryonic stem cells. The shorter isoform is the major transcript amplified from total RNA by reverse transcription (RT)-PCR and visualized on the protein level by Western blotting with common and isoformspecific antibodies. Transcripts of the longer A1E isoform have been identified in mouse, rat and human cerebellum, in in vitro, differentiated embryoid bodies, in the insulinoma cell lines INS-1 (rat) and βTC-3 (mouse), in the pituitary cell line AtT-20 (mouse) when grown in 5 mM glucose, and in islets of Langerhans (rat) and kidney (rat and human). The detection of different isoforms of A1E in cell lines and tissues shows that the wide expression of A1E has to be specified by identifying the corresponding isoforms in each tissue. In islets of Langerhans and in kidney, a distinct isoform called A1Ee has been determined by RT-PCR, while in cerebellum a set of different A1E structures has been detected, which might reflect the functional heterogeneity of cerebellar neurons. The tissue-specific expression of different isoforms might be related to specific functions, which are not yet known, but the expression of the new isoform A1Ee in islets of Langerhans and kidney leads to the suggestion that A1E might be involved in the modulation of the Ca 2ϩ -mediated hormone secretion.Keywords : A1E isoforms ; Ca 2ϩ channels ; islets of Langerhans; kidney; single-cell RT-PCR.Low and high voltage-gated Ca 2ϩ channels are subdivided, according to their threshold of activation and their different single channel conductances [1]. The pore-forming subunit of the first low voltage-activated T-type Ca 2ϩ channel has been cloned and functionally expressed recently as A1G [2].The group of six different high voltage-activated Ca 2ϩ channels (A1S-, A1C-, A1D-, A1A-, A1B-, A1E subunits) has been investigated intensively during the last decade [3,4]. They are subdivided into two different families, based on their primary sequence. The A1S, A1C, and A1D subunits are sensitive against the classical blockers of L-type Ca 2ϩ channels, the dihydropyridines, the phenylalkylamines and the benzothiazepines. The subfamily of the non-L-type A1 subunits share, among each other, a functional interaction with inhibitory G proteins [5]. The Ntype Ca 2ϩ channels (A1B) are blocked by ω-conotoxin-GVIA, the P-type and Q-type Ca 2ϩ channels (A1A) are discriminated byCorrespondence to T. Schneider,

R-type Calcium Channel Isoform in Rat Dorsal Root Ganglion Neurons

“…Among six isoforms (Cav2.3a, Cav2.3b, Cav2.3c, Cav2.3d, Cav2.3e, Cav2.3f), Cav2.3e is the major endocrine Cav2.3 isoform that was identified in rat and human kidney, insulinoma cell line INS-1 cells and islets of Langerhans [10]. We have shown that Cav2.3e is uniquely expressed in trkA-positive, IB4-negative DRG neurons that contain neuropeptide transmitters such as substance P and CGRP.…”

“…Six isoforms of the R-type Cav2.3 Ca 2+ channel (Cav2.3a∼ Cav2.3f) have been reported in various mammalian species [8][9][10][11][12]. R-type Ca 2+ channels are also present in DRG neurons [2], and have been suggested to play a critical role in the pain transmission and neuropathic pain [13,14].…”

CaV2.3 calcium channels control second-phase insulin release

“…It exhibits a relatively modest neurological phenotype, including altered pain responses (22), impaired spatial memory (23), and enhanced fear reaction (24). Pancreatic islets express the endocrine splice variant of Ca V 2.3 (25), and previous investigations of glucose homeostasis in Ca V 2.3 -/-mice have demonstrated a slight glucose intolerance and reduced glucoseinduced insulin secretion (26). Here we have extended these initial observations by performing in vivo glucose tolerance tests, dynamic measurements of phasic insulin secretion in situ, static pancreatic hormone-release experiments in isolated islets, as well as single cell recordings of whole-cell Ca 2+ currents and exocytosis and ratiometric measurements of the cytoplasmic Ca 2+ concentration in WT and Ca V 2.3 -/-islets.…”

Reduction of insulin secretion in the insulinoma cell line INS-1 by overexpression of a Ca(v)2.3 (alpha1E) calcium channel antisense cassette

“…The predicted structure of a1Ee in the insulinoma cell line INS-1 and in rat islets of Langerhans (15) is different from the cloned a1Ed (16) and a1E-1/a1E-3 variants (17). The a1Ee splice variant is characterized by a deletion of 19 amino acids in the II/III loop and an insertion of 43 amino acids in the carboxy terminus (15,18,19).…”