Oxytocin pretreatment of pregnant rat uterus inhibits Ca2+ uptake in plasma membrane and sarcoplasmic reticulum.
Myometrium from rats in varying stages of pregnancy (from 17 to 22 days) was treated with oxytocin (0.1-10 microM) and plasma membranes and sarcoplasmic reticulum were isolated using a Percoll gradient. When the myometrium had been treated with oxytocin, Ca2+ uptake was reduced by 29.4% in the plasma membrane and by 32.6% in the sarcoplasmic reticulum. The inhibitory action of oxytocin was highly dependent upon the stage of gestation: Only membranes from rats close to term (21-22 days) exhibited reduced Ca2+ transport activity after hormone treatment. This effect correlated highly with a significant decrease in the serum progesterone level of these animals. In plasma membrane vesicles, oxytocin reduced the maximal velocity of the Ca2+ pump without significantly affecting the affinity for Ca2+. Oxytocin did not affect the passive permeability of the plasma membranes, nor their proportion of sealed inside-out vesicles nor the amount of Ca2(+)-pump protein in these membranes. In addition, oxytocin caused no change in the passive permeability of the membrane nor in the rate of inositol trisphosphate-induced Ca2+ release from the sarcoplasmic reticulum. These results suggest that there is a specific action of oxytocin on the activity of the myometrial plasma membrane and sarcoplasmic reticulum Ca2+ pumps which may contribute to the maintenance of an elevated intracellular calcium level during parturition.
Magocsi
M
M
Department of Biochemistry and Molecular Biology, Mayo Clinic/Foundation, Rochester, MN 55905.
Penniston
J T
JT
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002147:Calmodulin / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism; D005260:Female; D005865:Gestational Age; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry; D009215:Myometrium / Q000378:metabolism; D010121:Oxytocin / Q000494:pharmacology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011374:Progesterone / Q000097:blood; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D014599:Uterus / Q000378:metabolism*
D002147:Calmodulin; D008565:Membrane Proteins; D011374:Progesterone; D010121:Oxytocin; D015544:Inositol 1,4,5-Trisphosphate; D002784:Cholesterol; D000252:Calcium-Transporting ATPases; D002118:Calcium