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Calcium-Activated Chloride Currents Prolongs the Duration of Contractions in Pregnant Rat Myometrial Tissue

Department of Obstetrics and Gynecology, University of Vermont, Burlington, Vermont, roger.young{at}uvm.edu

Adam Bemis, MS

BioRad Laboratories, Hercules, CA

We investigated the importance of pharmacologically blocking calcium-activated chloride (I_Cl(Ca)) and L-type calcium currents on isometric contractions of strips of D21 pregnant rat myometrial tissue, while simultaneously measuring the electrical activity of the tissue strips with extracellular contact electrodes. When measured with contact electrodes, the duration of the spiking activity directly reflects the duration of the tissue-level plateau potential. We correlated the number of spikes, durations of spiking activity, and the spiking frequencies with changes of the area under the force curves as a function of exposure to low doses of anthracene-9-carboxylate (9-AC, a non-specific Cl channel blocker), chlorotoxin (a specific I_Cl(Ca) blocker) and nifedipine (an L-type calcium channel blocker). The area under the force curve was measured only during spiking electrical activity, thereby separating pharmacological effects on tissue relaxation from those that modulate force production. Blocking chloride channels reduced impulse, shortened the duration of spiking activity, and reduced the number of spikes generated in each contraction. This was observed without a change in the frequency of spike production or a reduction of peak force. Nifedipine reduced impulse, shortened the duration of spiking activity, and reduced the number of spikes. In contrast to chloride channel blockade, nifedipine reduced maximum spike frequency and peak force. Taken together, our data suggest that blocking L-type calcium channels reduces impulse directly by reducing peak force, and indirectly by reducing activation of I_Cl(Ca) , which shortens the duration of the contraction.

Key Words: Myometrium • ICl(Ca) • nifedipine • chlorotoxin • chloride channels.

This version was published on August 1, 2009

Reproductive Sciences, Vol. 16, No. 8, 734-739 (2009)
DOI: 10.1177/1933719109334965


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