External alkalinization decreases intracellular Ca++ and spontaneous contractions in pregnant rat myometrium.
OBJECTIVE
As plasma pH rises during pregnancy, the effect of raising external pH on spontaneous contractions in pregnant rat myometrium was investigated to test the hypothesis that elevated external pH depresses contraction.


METHODS
Strips of longitudinal myometrium were loaded with SNARF (seminaphthorhodafluor) or Indo-1 for simultaneous intracellular pH or Ca++ and force measurements. Results were obtained from a minimum of five animals in each group, and significant differences were tested for by paired Student t tests.


RESULTS
Raising the external pH significantly reduced spontaneous force and calcium transient in the pregnant uterus. Raising the external pH led to a slow rise in intracellular pH, but this could not account for the functional effect. K+ rubidium 86-labeled efflux rates were unaffected by external pH, suggesting no hyperpolarization. The Ca++ channel agonist Bay K8644 (5 mumol/L) restored contractions abolished by raised external pH.


CONCLUSIONS
Raised external pH reduces spontaneous contractions in the pregnant rat uterus, probably by an external effect on Ca++ entry. This effect may contribute to uterine quiescence before term.
Taggart
M J
MJ
Physiological Laboratory, University of Liverpool, United Kingdom.
Sheader
E A
EA
Walker
S D
SD
Naderali
E K
EK
Moore
S
S
Wray
S
S
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001578:Benzopyrans; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D005260:Female; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007211:Indoles; D009215:Myometrium / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D011247:Pregnancy; D051381:Rats; D012414:Rubidium Radioisotopes / Q000378:metabolism; D014590:Uterine Contraction / Q000187:drug effects
D001578:Benzopyrans; D002120:Calcium Channel Agonists; D005456:Fluorescent Dyes; D007211:Indoles; D012414:Rubidium Radioisotopes; C063917:SNARF dye; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C048960:indo-1; D011188:Potassium; D002118:Calcium