Carboxyeosin decreases the rate of decay of the [Ca2+]i transient in uterine smooth muscle cells isolated from pregnant rats (original) (raw)

Abstract

In myometrial smooth muscle cells the rate of decline of intracellular calcium ([Ca2+]i) is determined by Ca2+ extrusion from the cell and uptake into intracellular stores. The relative quantitative contribution of these processes however, has not been established. We therefore examined the effect of the sarcolemmal Ca2+ pump inhibitor, carboxyeosin, on the rate of the [Ca2+]i transient decline in myocytes isolated from pregnant rat uterus. Indo-1 was used in conjunction with the whole-cell patch-clamp technique to measure [Ca2+]i simultaneously with transmembrane calcium current (I Ca). [Ca2+]i transients were elicited by repetitive membrane depolarization to simulate the natural pattern of uterine electrical activity. The rate of [Ca2+]i removal was calculated from the falling phase of the [Ca2+]i transient. Pre-treatment of the cells with 2 µM carboxyeosin led to a marked decrease in the rate of [Ca2+]i transient decay, suggesting that the sarcolemmal Ca2+ pump is involved in the calcium extrusion process. Removal of the extracellular Na also decreased the rate of [Ca2+]i decay, indicating an important role for the Na+/Ca2+ exchange. When both the sarcolemmal Ca2+ pump and Na+/Ca2+ exchange were inhibited the cell failed to restore [Ca2+]i after the stimulation. Comparison of the rate constants of [Ca2+]i decay in control conditions and after carboxyeosin treatment shows that approximately 30% of [Ca2+]i decay is due to the sarcolemmal calcium pump activity. The remaining 70% can be attributed to the activity of Na+/Ca2+ exchanger and the intracellular calcium stores.

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Authors and Affiliations

  1. Department of Physiology, University of Liverpool, Crown Street, Liverpool, L69 3BX, UK (e-mail: s.wray@liverpool.ac.uk, Tel.: +44 151 794 5306, Fax: +44 151 794 5321), , , , , , GB
    A. Shmigol & S. Wray
  2. Department of Veterinary Preclinical Sciences, University of Liverpool, Liverpool, L69 3BX, UK, , , , , , GB
    D. A. Eisner

Authors

  1. A. Shmigol
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  2. D. A. Eisner
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  3. S. Wray
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Received: 17 July 1998 / Received after revision: 23 September 1998 / Accepted: 25 September 1998

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Shmigol, A., Eisner, D. & Wray, S. Carboxyeosin decreases the rate of decay of the [Ca2+]i transient in uterine smooth muscle cells isolated from pregnant rats.Pflügers Arch 437, 158–160 (1998). https://doi.org/10.1007/s004240050761

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