Magnesium and potassium ions on tone and reactivity of human placental chorionic veins.
1. In vitro studies were undertaken to investigate the effects of external potassium [K+]0 2.4-7.1 mM and magnesium [Mg2+]0 0-4.8 mM concentration on human chorionic veins basal tone and on serotonin (5-HT)-induced contractions. 2. The higher the [Mg2+]0, the less the basal tension developed in isolated chorionic veins, irrespective of the [K+]0. 3. The EC50 value to 5-HT was enhanced by increases in [Mg2+]0, whereas the ability of 5-HT to induce a maximal contraction was attenuated. 4. The rightward shift of the concentration-response curves and reduced Emax response, observed when the concentration of [Mg2+]0 was raised, indicate a non-competitive antagonism of [Mg2+]0 with 5-HT. 5. The lack of an effect of [K+]0 on the EC50 and Emax values for 5-HT suggest that in this tissue the affinity of 5-HT for 5-HT receptors does not involve potassium. 6. These results suggest that basal tone and 5-HT-induced contractions of human chorionic vascular smooth muscle cells appear to be highly sensitive to alterations in extracellular Mg2+.
González
C
C
Departamento de Ciencias Fisiológicas, Facultad de Ciencias Biológicas, Universidad de Concepción, Chile.
Cruz
M A
MA
Gallardo
V
V
Varela
J
J
D002824:Chorionic Villi / Q000502:physiology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010920:Placenta / Q000098:blood supply; D011188:Potassium / Q000494:pharmacology*; D011247:Pregnancy; D012701:Serotonin / Q000494:pharmacology; D014680:Veins / Q000187:drug effects
D012701:Serotonin; D008274:Magnesium; D011188:Potassium