Differential modulation of L-type calcium channel subunits by oleate.
Nonesterified fatty acids such as oleate and palmitate acutely potentiate insulin secretion from pancreatic islets in a glucose-dependent manner. In addition, recent studies show that fatty acids elevate intracellular free Ca(2+) and increase voltage-gated Ca(2+) current in mouse beta-cells, although the mechanisms involved are poorly understood. Here we utilized a heterologous system to express subunit-defined voltage-dependent L-type Ca(2+) channels (LTCC) and demonstrate that beta-cell calcium may increase in part from an interaction between fatty acid and specific calcium channel subunits. Distinct functional LTCC were assembled in both COS-7 and HEK-293 cells by expressing either one of the EYFP-tagged L-type alpha(1)-subunits (beta-cell Cav1.3 or lung Cav1.2) and ERFP-tagged islet beta-subunits (ibeta(2a) or ibeta(3)). In COS-7 cells, elevations in intracellular Ca(2+) mediated by LTCC were enhanced by an oleate-BSA complex. To extend these findings, Ca(2+) current was measured in LTCC-expressing HEK-293 cells that revealed an increase in peak Ca(2+) current within 2 min after addition of the oleate complex, with maximal potentiation occurring at voltages <0 mV. Both Cav1.3 and Cav1.2 were modulated by oleate, and the presence of different auxiliary beta-subunits resulted in differential augmentation. The potentiating effect of oleate on Cav1.2 was abolished by the pretreatment of cells with triacsin C, suggesting that long-chain CoA synthesis is necessary for Ca(2+) channel modulation. These results show for the first time that two L-type Ca(2+) channels expressed in beta-cells (Cav1.3 and Cav1.2) appear to be targeted by nonesterified fatty acids. This effect may account in part for the acute potentiation of glucose-dependent insulin secretion by fatty acids.
Tian
Yingrao
Y
Department of Pharmacology and Toxicology, Virginia Commonwealth University Medical Center, Richmond, VA, USA.
Corkey
Richard F
RF
Yaney
Gordon C
GC
Goforth
Paula B
PB
Satin
Leslie S
LS
Moitoso de Vargas
Lina
L
D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry; D019556:COS Cells; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002522:Chlorocebus aethiops; D004594:Electrophysiology / Q000379:methods; D006801:Humans; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D008164:Luminescent Proteins / Q000737:chemistry; D019301:Oleic Acid / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D010957:Plasmids; D014162:Transfection; D000097573:Red Fluorescent Protein
D001426:Bacterial Proteins; D002118:Calcium; D020746:Calcium Channels, L-Type; D008164:Luminescent Proteins; D019301:Oleic Acid; D000097573:Red Fluorescent Protein; C054562:yellow fluorescent protein, Bacteria