title: Measurement of the total concentration of functional Na+, K(+)-pumps in rumen epithelium.
abstract: Using the technique of vanadate-facilitated [3H]ouabain binding we have developed a simple and reliable assay for measuring the concentration of [3H]ouabain binding sites in small fresh or frozen biopsies of rumen epithelium papillae. In bovine and ovine rumen epithelium obtained from the cranio-ventral rumen sac the concentration of [3H]ouabain binding sites was 1.6-4.9 nmol g dry wt-1 (n = 32) and 3.7-5.2 nmol g dry wt-1 (n = 6), respectively. When incubated in oxygenated Krebs-Ringer bicarbonate buffer fresh biopsies of rumen epithelium maintained a high K+ and low Na+ content for at least 6 h. Na+ loading of the biopsies induced about 20-fold increase of the Na+, K(+)-pump activity based on measurement of ouabain suppressible net [86Rb+] influx. The ouabain suppressible net influx of [86Rb+] measured in Na+ loaded biopsies showed a close correlation to the [3H]ouabain binding capacity (r = 0.80, P < 0.01) and corresponded to 47 +/- 2% (n = 9) of the theoretical maximum flux rate. The ouabain suppressible net influx of K+ and [86Rb+] were linearly related (r = 0.73; P < 0.001). The net Na+ efflux was 1.21 times the net K+ influx. It is concluded that rumen epithelium has a large capacity for active Na+/K+ transport and that there is agreement between the concentration of [3H]ouabain binding sites in the epithelium and the ouabain suppressible rate of net [86Rb+] influx in Na+ loaded biopsies in spite of some uncertainty about the maximum turnover number of the Na+, K(+)-pump in rumen epithelium.
authors.affiliation: Institute of Physiology, University of Aarhus, Denmark.
authors.forename: N B
authors.initials: NB
authors.lastname: Kristensen
authors.forename: O
authors.initials: O
authors.lastname: Hansen
authors.forename: T
authors.initials: T
authors.lastname: Clausen
mesh_terms: D000042:Absorption / Q000502:physiology; D000818:Animals; D001706:Biopsy; D002417:Cattle; D004848:Epithelium / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D012417:Rumen / Q000166:cytology / Q000378:metabolism*; D012756:Sheep; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: C028996:cardiac glycoside receptors; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium