Characterization of [<sup>3</sup>H]‐nitrendipine binding to uterine smooth muscle plasma membrane and its relevance to inhibition of calcium entry

1Spontaneous and potassium chloride (KCI)-induced tension development of strips of whole uterus from the day-22 pregnant rat was reduced when the tissues were incubated in a calcium ion (Ca2')-free medium. 2 Strips of whole uterus, in an initially Ca2 -free medium, responded to the cumulative addition of Ca2" with graded phasic tension development and associated rapid electrical discharges. The spasms were inhibited by gallopamil (100 nM) and diltiazem (I JM). 3 Strips of whole uterus in a depolarizing (40mM K+) medium, which was initially Ca2+-free, responded to the cumulative addition of Ca2+ with graded tonic tension development without associated electrical discharges. These spasms were inhibited by calcium entry blockers with a rank order of potency of nifedipine = gallopamil > diltiazem > cinnarizine. 4 KCl-induced tension development in endometrium-free uterine strips was antagonized by calcium entry blockers with a rank order of potency of nifedipine > gallopamil> diltiazem> cinnarizine. 5 Ca2+ influx into endometrium-free uterine strips was assessed by means of the 'lanthanum method'. KCl induced a concentration-dependent increase in 45Ca2+ influx which was suppressed or abolished by nifedipine (2.5 nM), gallopamil (100 nM), diltiazem (500 nM) or cinnarizine (5 JAM). 6 It is concluded that spontaneous and KCI-induced tension development of rat uterus involves Ca2+ influx from the extracellular medium into the myometrial cell. These results support the hypothesis that nifedipine, gallopamil, diltiazem and cinnarizine inhibit Ca2+-and KCI-induced tension development of rat uterus by reduction of Ca2" influx.

Section: Discussionmentioning

confidence: 99%

Effects of calcium entry blockers on tension development and calcium influx in rat uterus

Granger

Hollingsworth

Weston

1986

“…The influx ofextracellular calcium through membrane calcium channels is considered to be of major importance for the initiation of contraction in smooth muscle. Data on the characterization of membrane channels for calcium entry in the rat myometrium, using nitrendipine as the radioligand, were recently presented (Batra, 1985). In the present study the effect ofoestrogen treatment on both net influx ofcalcium in the intact uterine smooth muscle and density of calcium channels, in the isolated membranes of ovariectomized rats, was examined.…”

Section: Introductionmentioning

confidence: 99%

“…The various subcellular fractions were isolated by a method essentially similar to that described by JaquaSteweart et al (1979) with some modifications (Batra, 1985). The tissue was homogenized in about 4 volumes of sucrose-HEPES (sucrose 0.25 M and HEPES 10mM) buffer with a Polytron homogenizer (PGA 10-35) for 2 s at one half speed.…”

Section: Preparation Of Subcellular Fractionsmentioning

confidence: 99%

“…The pooled supernatant was filtered through two layers of gauze and the filtrate centrifuged at 175,000 g for 20 min in a Beckman L-5-65 centrifuge. The supernatant was discarded and the pellet, which represented crude membrane preparation, was suspended in 20ml of buffer and subjected subsequently to centrifugation on a discontinuous sucrose gradient as described previously (Batra, 1985). Bands containing plasma membrane (PM), endoplasmic reticulum (ER) and mitochondria (M) were successively aspirated from the top of the centrifuge tube.…”

Section: Preparation Of Subcellular Fractionsmentioning

confidence: 99%

See 1 more Smart Citation

Increase by oestrogen of calcium entry and calcium channel density in uterine smooth muscle

Batra

1987

Self Cite

The effect of in vivo oestrogen treatment on both 45Ca influx in myometrial strips and the kinetics of [3H)‐nitrendipine binding in the isolated plasma membrane (PM) was studied. After four days of continuous oestrogen treatment of ovariectomized rats, 45Ca influx in both resting (unstimulated) and K‐stimulated myometrium was substantially increased. Oestrogen treatment significantly increased the density in PM of nitrendipine binding sites and also caused a slight and insignificant increase in the affinity for nitrendipine. The data suggest that the increase in Ca entry following oestrogen treatment prol ably results from an increase in calcium channel density.

“…Each point is the mean of at least five determinations. (Johnson & Fugman, 1983;Kreye et al, 1983;Spedding, 1984;Batra, 1985).…”

Section: Introductionmentioning

confidence: 99%

Effect of calcium and calmodulin antagonists on contractile responses of the human uterine artery

Kostrzewska

Laudański

Batra

1988

Self Cite

0.7 and 10pUM. 4 Calmodulin antagonists, particularly trifluoperazine and flunarizine, caused a greater inhibition of the NA than of the K response. 5 These results indicate that besides the extracellular calcium which appears to be the major source of activator calcium, there is an intracellular pool of calcium which can be utilized to activate, albeit to a limited extent, drug-induced contractile responses.