Tissue specificity and alternative splicing of the Na+/Ca2+ exchanger isoforms NCX1, NCX2, and NCX3 in rat

Abstract

The gene coding for the Na+/Ca2+ exchanger NCX1 is characterized by a cluster of six exons (A, B, C, D, E, and F) coding for a variable region in the COOH terminus of the large intracellular loop of the protein. Alternative splicing of these exons generates multiple tissue-specific variants of NCX1. Using reverse transcriptase-polymerase chain reaction, we analyzed eight previously described and four new splicing isoforms of NCX1 in a wide variety of tissues and cells. Exons A and B are mutually exclusive, as shown in earlier studies, and splicing isoforms containing exon A are preferentially expressed in heart, brain, and skeletal muscle, whereas splicing variants with exon B are found in all rat tissues except heart. The second and third isoforms of the Na+/Ca2+ exchanger, NCX2 and NCX3, show a deletion of 37 amino acids in the intracellular loop corresponding to parts of the variable region of NCX1. We identified three splicing isoforms of NCX3 in brain and skeletal muscle by reverse transcriptase-polymerase chain reaction. These splice variants are generated by including either of two alternative exons equivalent to the NCX1 exon A or B and by including or excluding a sequence equivalent to the NCX1 exon C. We did not detect any alternative splicing of NCX2. We examined selected tissues from neonatal and adult rats and found developmental regulation for NCX1 and NCX3 splicing isoforms in skeletal muscle. Specific isoform patterns were also detected for NCX1 and NCX3 in cultured cortical neurons, astrocytes, and oligodendrocytes. We suggest a new terminology to distinguish the different splice variants of individual NCX isoforms.

Plasma membrane calcium ATPases (PMCAs) as potential targets for the treatment of essential hypertension

“…Thus, modulation of mechanisms which decrease cytoplasmic Ca 2+ can modulate arterial contractility and may thus be a potential target for reduction of BP. Ca 2+ can be extruded out of VSMCs by two different Ca 2+ transporting systems, the Na + /Ca 2+ exchanger (NCX), predominantly type 1 (NCX1) (Quednau et al, 1997), and plasma membrane calcium ATPase type 1 or 4 (PMCA1, PMCA4) (Oloizia & Paul, 2008). In the heart, NCX plays a major role in Ca 2+ extrusion extruding one Ca 2+ out of the cell in exchange for three Na + ions (Bers, 2000).…”

Gangliosides of the nuclear membrane: A crucial locus of cytoprotective modulation

“…Current studies in our laboratory appear to support this hypothesis in that Jurkat cells, which lack NCX, show NCX expression in the NE when transfected with plasmid containing the BCDEF isoform of NCX1 (work in preparation). The B exon was shown to contain four Arg residues [Quednau et al, 1997;Van Eylen et al, 2001], the positive charge of which could interact with the negative charge of GM1 to form the high affinity complex. This is in contrast to the A exon, hypothesized to be targeted to the plasma membrane, which contains only one Arg and might be less likely to associate tightly with GM1.…”

Cardiac Na+–Ca2+ exchanger current induced by tyrphostin tyrosine kinase inhibitors

“…A key question is whether the tyrphostin acted by influencing tyrosine phosphorylation. In that regard, it is known that NCX1 has consensus sites for phosphorylation by TK (Quednau et al, 1997), and that tyrosine phosphorylation of NCX regulatory protein can modulate basal NCX activity (Kiang et al, 2003). Evidence in favour of a phosphorylation-related mechanism is that a second TK inhibitor (A25) was as effective as A23, the TKinactive analogue (A1) was substantially less effective, and PTP inhibitor orthovanadate antagonized the action of A23.…”