Figure 5. Role of extracellular as well as intracellular calcium in Tg-induced uterine contractions and MLC20 phosphorylation.

(A) Representative recordings of the cumulative dose responses on myometrial strips induced by Tg or PGF-2α in calcium-free solution. After the stimulators were increased to the maximal effective dose, calcium was added to a final concentration of 1.8 mmol/L. (B) Representative antibody reaction blots for the relative levels of MLC20 and pMLC20 in protein samples from Tg (400 nM) -treated or untreated rat myometrial cells in the presence or absence of extracellular Ca²⁺. (C) Inhibitory effects of cumulative doses of nitrendipine on contractile responses after stimulation with Tg or PGF-2α in rat myometrial strips (n = 3). Contractions were measured as the area under the curve (AUC) and expressed as a percentage of the response to 5 µM Tg or 450 nM PGF-2α. (D–E) Representative antibody reaction blots for the relative levels of MLC20 and pMLC20 in protein samples from Tg (400 nM) -treated or untreated rat myometrial cells in the presence or absence of thapsigargin (2.5 µM) (D). Signal intensities for MLC20 and pMLC20 from three different blots were used for the quantitative analyses (E). (F) Inhibitory effects of cumulative doses of Rethenium red on contractile responses after stimulation with Tg in rat myometrial strips (n = 3). Contractions were measured as the area under the curve (AUC) and expressed as a percentage of the response to 5 µM Tg. Data are expressed as means ± SEM. *** P<0.001 and ** P<0.01 compared to control.