Mediators involved in the rat uterus contraction in calcium-free solution

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1. 1. The effect of (Na + + K +)-ATPase inhibitor ouabain (10 −5−3 × 10 −4 M), and the (Ca 2+ + Mg 2+)-ATPase inhibitors vanadate (6 × 10 −6−6 × 10 −4 M), oxytocin (2 × 10 −9−4 × 10 −8 M), and prostaglandin F 2α (PGF 2α, 10 −7−6 × 10 −6 M) were assayed on rat 2. 2. Vanadate, oxytocin and PGF 2α, but not ouabain, induced contractions in a dose-dependent way (ED 50: 7.5 ± 0.03 × 10 −5 M; 6.5 ± 0.064 × 10 −9 M and 3.8 ± 0.085 × 10 −7 M). 3. 3. Vanadate (3 × 10 −4 M) and oxytocin (OT, 10 mU/ml = 2 × 10 −8 M)-induced tonic contraction were not modified by nifedipine (10 −10–10 −6 M), monensin (10 −5−3 × 10 −4 M) or amiloride (10 −5–10 −3 M). 4. 4. The intracellular calcium release inhibitors TMB-8 (10 −6–10 −4 M) and dantrolene (3 × 10 −6–10 −4 M), and the prostaglandin release inhibitor indomethacin (3 × 10 −8−6 × 10 −5 M) relaxed the vanadate and OT-induced tonic contractions. 5. 5. The calmodulin inhibitors trifluoperazine ( 3 × 10 −5−3 × −4 M ), bepridil (10 −8−3 × 10 −4 M), calmida (10 −7–10 −4 M) and W-7 (10 −7–10 −5 M) also relaxed the vanadate and OT-induced tonic contractions. 6. 6. Our results suggest that oxytocin and vanadate-induced contractions on rat uterus in Ca-free medium could be produced by release of prostaglandins and intracellular calcium, and mediated by calmodulin.