title: Nardilysin convertase regulates the function of the maxi-K channel isoform mK44 in human myometrium.
abstract: In smooth muscle, large-conductance Ca(2+)- and voltage-activated K(+) channels from the gene KCNMA (maxi-K channels) generate isoforms with disparate responses to contractile stimuli. We previously showed that the human myometrium expresses high levels of the splice variant of the maxi-K channel containing a 44-amino acid insertion (mK44). The studies presented here demonstrate that nardilysin convertase, a Zn(2+)-dependent metalloprotease of the insulinase family, regulates the plasma membrane expression of mK44 and its response to increases in intracellular Ca(2+). We show that nardilysin convertase isoform 1 is present in human myometrium and colocalizes with mK44. Studies indicate that nardilysin convertase regulates 1) retention of the mK44 COOH-terminal fragment in the endoplasmic reticulum in quiescent myometrial smooth muscle and 2) Ca(2+)-induced translocation of mK44 to the plasma membrane. In mouse fibroblasts, nardilysin convertase significantly attenuates mK44-dependent current. In human myometrial smooth muscle cells, inhibition of nardilysin convertase promotes membrane localization of mK44 and an increase in maxi-K current. Overall, our data indicate that, in human myometrium, nardilysin convertase and mK44 channels are a part of the molecular mechanism that regulates the excitability of smooth muscle cells.
authors.affiliation: Dept. of Molecular Physiology and Biophysics, 6-432 BSB, Iowa City, IA 52242-1109, USA.
authors.forename: Victoria P
authors.initials: VP
authors.lastname: Korovkina
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Stamnes
authors.forename: Adam M
authors.initials: AM
authors.lastname: Brainard
authors.forename: Sarah K
authors.initials: SK
authors.lastname: England
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000201:enzymology; D005260:Female; D005347:Fibroblasts / Q000201:enzymology; D006801:Humans; D007527:Isoenzymes; D007700:Kinetics; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology*; D009215:Myometrium / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D011188:Potassium / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D020033:Protein Isoforms; D021381:Protein Transport; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection; D014590:Uterine Contraction
chemical_list: D007527:Isoenzymes; C494841:KCNMA1 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D011480:Protease Inhibitors; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D008666:Metalloendopeptidases; C087976:nardilysin; D011188:Potassium; D002118:Calcium