title: Effects of magnesium and terbutaline on contractility and K+ uptake in isolated human uterine muscle.
abstract: Mg++ (3 and 6 mmol/L), the beta 2-adrenergic agonist terbutaline (1 and 10 mumol/L), and dibutyryl cyclic adenosine 5'-monophosphate (0.1 and 1 mmol/L) suppressed spontaneous activity and the increase in contractile activity induced by ouabain or K(+)-free buffer in isolated human pregnant myometrium. The ouabain-suppressible rubidium 86 or potassium 42 uptake was unaffected by the presence of Mg++ (3 and 6 mmol/L), the beta 2-adrenergic agonist terbutaline (1 and 10 mumol/L), or dibutyryl cyclic adenosine 5'-monophosphate (1 mmol/L). However, loading of the strips with Na+ and incubation in high K+ induced a fivefold increase in rubidium 86 uptake. On the basis of these flux rates, our previous data on the total concentration of sodium-potassium pumps in the human myometrium, and an estimated maximum transport rate of the sodium-potassium pump of 8900 K+ ions per minute at 30 degrees C, it could be calculated that the sodium-potassium pump in the Na(+)-loaded strips reached around 80% of its maximal rate. Taken together, these results showed that the relaxant effects of Mg++, terbutaline, and dibutyryl cyclic adenosine 5'-monophosphate on human myometrium are not due to a stimulation of active sodium-potassium transport.
authors.affiliation: Department of Obstetrics and Gynecology, University of Aarhus, Denmark.
authors.forename: K
authors.initials: K
authors.lastname: Skajaa
authors.forename: M E
authors.initials: ME
authors.lastname: Everts
authors.forename: T
authors.initials: T
authors.lastname: Clausen
authors.forename: A
authors.initials: A
authors.lastname: Forman
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology*; D009215:Myometrium / Q000187:drug effects*; D011188:Potassium / Q000493:pharmacokinetics; D012414:Rubidium Radioisotopes / Q000493:pharmacokinetics; D012964:Sodium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects; D013726:Terbutaline / Q000494:pharmacology*; D013997:Time Factors; D014590:Uterine Contraction / Q000187:drug effects*
chemical_list: D007328:Insulin; D012414:Rubidium Radioisotopes; D005576:Colforsin; D003994:Bucladesine; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D013726:Terbutaline; D011188:Potassium