Molecular diversity and functional characterization of voltage-dependent calcium channels (CACN4) expressed in pancreatic beta-cells.
Dihydropyridine-sensitive voltage-dependent calcium channels (VDCC) play a crucial role in insulin secretion. We recently have cloned a human alpha 1-subunit of the VDCC expressed in pancreatic beta-cells, designated CACN4. In this study we have isolated complementary DNAs encoding two forms of rat CACN4 (rCACN4A and rCACN4B) from a rat insulinoma RINm5F complementary DNA library. Rat CACN4A is a protein of 2203 amino acids and is the rat homolog of human CACN4, whereas rCACN4B lacks 535 amino acids in the carboxyl-terminal region, probably due to alternative splicing. We have found two additional variations, one in the intracellular loop between repeats I and II and the other in the extracellular region between the third and fourth segments of repeat IV. Reverse transcriptase-polymerase chain reaction analysis of rat pancreatic islet messenger RNA reveals that these variants are present in pancreatic islets. In addition, whole-cell voltage-clamp recordings of Chinese hamster ovary cells stably expressing the alpha 1-subunit (rCACN4A or rCACN4B) with or without the calcium channel beta 2-subunit show that coexpression of rCACN4A with the beta 2-subunit or rCACN4B with the beta 2-subunit elicits L-type VDCC currents, whereas expression of the alpha 1-subunit alone does not, indicating that CACN4 can associate functionally with the beta 2-subunit and that the beta-subunit is essential for functional expression of CACN4. These results suggest that there are various subtypes of CACN4 expressed in pancreatic beta-cells, and that both rCACN4A and rCACN4B can function as VDCC. Furthermore, the present study suggests that the expression of the beta-subunit as well as the alpha 1-subunit may participate in the regulation of insulin secretion.
Ihara
Y
Y
Department of Metabolism and Clinical Nutrition Kyoto University Faculty of Medicine, Japan.
Yamada
Y
Y
Fujii
Y
Y
Gonoi
T
T
Yano
H
H
Yasuda
K
K
Inagaki
N
N
Seino
Y
Y
Seino
S
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D020746:Calcium Channels, L-Type; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D006801:Humans; D007340:Insulinoma / Q000473:pathology; D015640:Ion Channel Gating; D007515:Islets of Langerhans / Q000378:metabolism*; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000473:pathology; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D012326:RNA Splicing; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D018076:DNA, Complementary; D009124:Muscle Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C093712:Cacna1d protein, rat; D002118:Calcium