Inhibition of beta-cell sodium-calcium exchange enhances glucose-dependent elevations in cytoplasmic calcium and insulin secretion.
OBJECTIVE
The sodium-calcium exchanger isoform 1 (NCX1) regulates cytoplasmic calcium (Ca(2+)(c)) required for insulin secretion in beta-cells. NCX1 is alternatively spliced, resulting in the expression of splice variants in different tissues such as NCX1.3 and -1.7 in beta-cells. As pharmacological inhibitors of NCX1 splice variants are in development, the pharmacological profile of beta-cell NCX1.3 and -1.7 and the cellular effects of NCX1 inhibition were investigated.


METHODS
The patch-clamp technique was used to examine the pharmacological profile of the NCX1 inhibitor KB-R7943 on recombinant NCX1.3 and -1.7 activity. Ca(2+) imaging and membrane capacitance were used to assess the effects of KB-R7943 on Ca(2+)(c) and insulin secretion in mouse and human beta-cells and islets.


RESULTS
NCX1.3 and -1.7 calcium extrusion (forward-mode) activity was approximately 16-fold more sensitive to KB-R7943 inhibition compared with cardiac NCX1.1 (IC(50s) = 2.9 and 2.4 vs. 43.0 micromol/l, respectively). In single mouse/human beta-cells, 1 micromol/l KB-R7943 increased insulin granule exocytosis but was without effect on alpha-cell glucagon granule exocytosis. KB-R7943 also augmented sulfonylurea and glucose-stimulated Ca(2+)(c) levels and insulin secretion in mouse and human islets, although KB-R7943 was without effect under nonstimulated conditions.


CONCLUSIONS
Islet NCX1 splice variants display a markedly greater sensitivity to pharmacological inhibition than the cardiac NCX1.1 splice variant. NCX1 inhibition resulted in glucose-dependent increases in Ca(2+)(c) and insulin secretion in mouse and human islets. Thus, we identify beta-cell NCX1 splice variants as targets for the development of novel glucose-sensitive insulinotropic drugs for type 2 diabetes.
Hamming
Kevin S C
KS
Department of Pharmacology, Alberta Diabetes Institute and Cardiovascular Research Centre, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
Soliman
Daniel
D
Webster
Nicola J
NJ
Searle
Gavin J
GJ
Matemisz
Laura C
LC
Liknes
David A
DA
Dai
Xiao-Qing
XQ
Pulinilkunnil
Thomas
T
Riedel
Michael J
MJ
Dyck
Jason R B
JR
Macdonald
Patrick E
PE
Light
Peter E
PE
D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004594:Electrophysiology; D005089:Exocytosis / Q000187:drug effects; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D020033:Protein Isoforms / Q000378:metabolism; D034741:RNA, Small Interfering; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D007328:Insulin; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D013890:Thiourea; D005947:Glucose; D002118:Calcium