Article date: February 1984
By: C. Lalanne, C. Mironneau, J. Mironneau, J.P. Savineau in Volume 81, Issue 2, pages 317-326
The effects of acetylcholine (ACh, 10−4m) and angiotensin II (Ang II, 10−6 M) have been studied on the mechanical and electrical activities of rat myometrial strips perfused in Ca2+‐free EGTA‐containing solutions.
Both ACh and Ang II produced transient contractions, the amplitude of which can be taken as a measurement of the amount of Ca2+ present in a drug‐sensitive Ca2+ store. The degree of filling of this store depended on the external Ca2+ concentration, and on the presence of contractile responses during the Ca2+ loading period. The existence of two pathways (either direct or transcytoplasmic) is suggested for Ca2+ uptake into the internal Ca2+ store.
The rate of filling of the Ca2+ store in 2.1 mm‐Ca2+‐containing solution was faster (time to half‐maximal response, t1/2 = 29 ± 2.2s, n = 4) than the rate of depletion in Ca2+‐free solution (t1/2 = 3 ± 0.3 min, n = 3). The gradual depletion of this store was much slower at 18°C than at 35°C, and in the presence of vanadate which is known to inhibit Ca2+‐ATPases.
Methoxyverapamil (D600, 10−6‐10−5m) had no appreciable effect on the direct Ca2+ uptake or on the release of Ca2+ from the store by ACh and Ang II. Mn2+ (10−3m) completely inhibited the direct pathway to the internal Ca2+ store and also reduced the release of Ca2+.
ACh and Ang II induced repetitive depolarizations close to zero potential which did not parallel the transient contractions as a function of the time of perfusion in Ca2+‐free solution. Applications of 2 mm EGTA, 135 mm K+ or Ca2+ antagonists which suppressed or reduced the drug‐induced depolarizations did not affect appreciably the drug‐induced contractions.
These results suggest that myometrial cells have an intracellular Ca2+ store sensitive to different stimulus substances. This store is not affected by depolarization of the plasma membrane and is certainly different from that described in voltage‐clamp experiments.
The effects of acetylcholine (ACh, 10−4m) and angiotensin II (Ang II, 10−6 M) have been studied on the mechanical and electrical activities of rat myometrial strips perfused in Ca2+‐free EGTA‐containing solutions.
Both ACh and Ang II produced transient contractions, the amplitude of which can be taken as a measurement of the amount of Ca2+ present in a drug‐sensitive Ca2+ store. The degree of filling of this store depended on the external Ca2+ concentration, and on the presence of contractile responses during the Ca2+ loading period. The existence of two pathways (either direct or transcytoplasmic) is suggested for Ca2+ uptake into the internal Ca2+ store.
The rate of filling of the Ca2+ store in 2.1 mm‐Ca2+‐containing solution was faster (time to half‐maximal response, t1/2 = 29 ± 2.2s, n = 4) than the rate of depletion in Ca2+‐free solution (t1/2 = 3 ± 0.3 min, n = 3). The gradual depletion of this store was much slower at 18°C than at 35°C, and in the presence of vanadate which is known to inhibit Ca2+‐ATPases.
Methoxyverapamil (D600, 10−6‐10−5m) had no appreciable effect on the direct Ca2+ uptake or on the release of Ca2+ from the store by ACh and Ang II. Mn2+ (10−3m) completely inhibited the direct pathway to the internal Ca2+ store and also reduced the release of Ca2+.
ACh and Ang II induced repetitive depolarizations close to zero potential which did not parallel the transient contractions as a function of the time of perfusion in Ca2+‐free solution. Applications of 2 mm EGTA, 135 mm K+ or Ca2+ antagonists which suppressed or reduced the drug‐induced depolarizations did not affect appreciably the drug‐induced contractions.
These results suggest that myometrial cells have an intracellular Ca2+ store sensitive to different stimulus substances. This store is not affected by depolarization of the plasma membrane and is certainly different from that described in voltage‐clamp experiments.
DOI: 10.1111/j.1476-5381.1984.tb10081.x
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