Splice variant-dependent regulation of beta-cell sodium-calcium exchange by acyl-coenzyme As.
The sodium-calcium exchanger isoform 1 (NCX1) is intimately involved in the regulation of calcium (Ca(2+)) homeostasis in many tissues including excitation-secretion coupling in pancreatic beta-cells. Our group has previously found that intracellular long-chain acyl-coenzyme As (acyl CoAs) are potent regulators of the cardiac NCX1.1 splice variant. Despite this, little is known about the biophysical properties of beta-cell NCX1 splice variants and the effects of intracellular modulators on their important physiological function in health and disease. Here, we show that the forward-mode activity of beta-cell NCX1 splice variants is differentially modulated by acyl-CoAs and is dependent both upon the intrinsic biophysical properties of the particular NCX1 splice variant as well as the side chain length and degree of saturation of the acyl-CoA moiety. Notably, saturated long-chain acyl-CoAs increased both peak and total NCX1 activity, whereas polyunsaturated long-chain acyl-CoAs did not show this effect. Furthermore, we have identified the exon within the alternative splicing region that bestows sensitivity to acyl-CoAs. We conclude that the physiologically relevant forward-mode activity of NCX1 splice variants expressed in the pancreatic beta-cell are sensitive to acyl-CoAs of different saturation and alterations in intracellular acyl-CoA levels may ultimately lead to defects in Ca(2+)-mediated exocytosis and insulin secretion.
Hamming
Kevin S C
KS
Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Riedel
Michael J
MJ
Soliman
Daniel
D
Matemisz
Laura C
LC
Webster
Nicola J
NJ
Searle
Gavin J
GJ
MacDonald
Patrick E
PE
Light
Peter E
PE
D000214:Acyl Coenzyme A / Q000737:chemistry / Q000378:metabolism*; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D005089:Exocytosis / Q000502:physiology; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D010171:Palmitoyl Coenzyme A / Q000737:chemistry / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D016415:Sequence Alignment; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D000214:Acyl Coenzyme A; D020033:Protein Isoforms; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D010171:Palmitoyl Coenzyme A; D012964:Sodium; D002118:Calcium