Stretch-induced enhancement of contractions in uterine smooth muscle of XXXX .

@entity398 @entity141 @entity3360 @entity593 @entity19643 @entity3897 @entity35
1. We studied the effect of servo-controlled stretch of smooth muscle strips from @entity35 uterus on tension and intracellular @entity141 concentration ([ @entity141 ]i, using @entity593 as an indicator) at 30 degrees C. 2. When quiescent uterine muscle strips were stretched at a ramp time of 0.5 s by multiples of 5% of the resting muscle length (L0) up to 40%, forty-two out of sixty muscle strips responded with a transient active contraction and a [ @entity141 ]i increase. The minimum excursion of stretch required for contraction was 26.3 +/- 7.5% of L0 (mean +/- S.D.). The peak response had an all-or-none property and was almost independent of the duration of stretch. 3. Stretches of 30 or 35% of L0 induced contraction in most cases when rapidly applied in 0.2-0.5 s, but slowly applied stretch (ramp duration of 5-10 s) rarely induced contraction. 4. The stretch-induced response was inhibited by the removal of extracellular @entity141 or by the addition of 10 nM @entity3360 . However, it was unaffected by 1 microM tetrodotoxin, 1 microM @entity3897 or by 10 microM @entity19643 , an inhibitor of @entity141 -ATPase in intracellular @entity141 stores. 5. When a stretch of 15-35% of L0 was applied during the relaxation phase of 10 nM @entity398 -induced rhythmic contractions, the first contraction after the stretch occurred earlier than that expected from the control rhythm. However, the frequency of the subsequent rhythm returned to almost the control level even during continued application of stretch, although the half-width of rhythmic contractions was increased during stretch. 6. The present study demonstrates that stretch of uterine muscle induces a transient contraction due to @entity141 influx, which is myogenic and dependent on the excursion and velocity of stretch. The all-or-none property of the stretch-induced contractions suggests initiation of @entity141 spikes. Furthermore, stretch modulates the @entity398 -induced rhythmic contractions.
