title: Sodium-calcium exchange in sarcolemmal vesicles from tracheal smooth muscle.
abstract: Sarcolemmal vesicles prepared by a new procedure from bovine tracheal smooth muscle were found to have a Na-Ca exchange activity that is significantly higher than that reported for different preparations from other types of smooth muscle. The exchange process system co-purified with 5'-nucleotidase, a plasma membrane marker enzyme, and was significantly enriched (over 100-fold) compared to mitochondria (cytochrome-c oxidase) but only slightly enriched (4-fold) compared to sarcoplasmic reticulum (NADPH-cytochrome-c reductase). The Na+ dependence of Ca2+ transport was demonstrated through both uptake and efflux procedures. The uptake profile with respect to Ca2+ was monotonic with a linear vo VS. vo.S-1 plot. The resultant Km of Ca2+ from the airway sarcolemmal vesicles (20 microM) was similar in magnitude to the Km of cardiac sarcolemmal vesicles (30 microM). Tracheal vesicles demonstrated a Vmax of 0.3-0.5 nmol.mg-1.s-1 which is significantly higher than that reported in preparations from other smooth muscle types. Furthermore, two processes found to stimulate cardiac Na-Ca exchange, pretreatment with either a mixture of dithiothreitol and Fe2+ or with chymotrypsin, were ineffective on the tracheal smooth muscle. Thus, the Na-Ca exchanger identified in tracheal smooth muscle appears to be different from that observed in cardiac muscle, implying that regulation of this activity may also be different.
authors.affiliation: Allergy and Inflammation Research, Hoffmann-La Roche Inc., Nutley, NJ.
authors.forename: R S
authors.initials: RS
authors.lastname: Slaughter
authors.forename: A F
authors.initials: AF
authors.lastname: Welton
authors.forename: D W
authors.initials: DW
authors.lastname: Morgan
mesh_terms: D015720:5'-Nucleotidase; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002458:Cell Fractionation; D002469:Cell Separation; D002498:Centrifugation; D004533:Egtazic Acid / Q000494:pharmacology; D003576:Electron Transport Complex IV / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D009708:Nucleotidases / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D012508:Sarcolemma / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014132:Trachea / Q000378:metabolism*
chemical_list: D000001:Calcimycin; D004533:Egtazic Acid; D011189:Potassium Chloride; D012964:Sodium; D009251:NADPH-Ferrihemoprotein Reductase; D003576:Electron Transport Complex IV; D009708:Nucleotidases; D015720:5'-Nucleotidase; D002118:Calcium