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Calcium Wave Evoked by Activation of Endogenous or Exogenously Expressed Receptors in Xenopus oocytes
Gary Brooker, Takashi Seki, Dennis Croll and Claes Wahlestedt
Proceedings of the National Academy of Sciences of the United States of America
Vol. 87, No. 7 (Apr., 1990), pp. 2813-2817
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/2354314
Page Count: 5
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The mRNA encoding the cloned substance K receptor was microinjected into Xenopus laevis oocytes. After expression of the mRNA, Ca2+ was imaged in the oocytes with a digital imaging fluorescence microscopy system using the Ca2+-sensitive dyes fura-2 and fluo-3. Application of substance K caused a dose-related wave of Ca2+ mobilization to spread from a focus and to elevate the Ca2+ concentration in the oocyte. Activation of endogenous muscarinic or angiotensin II receptors in noninjected oocytes evoked a similar response. The Ca2+ rise in oocytes induced by substance K was due to internal Ca2+ mobilization and was independent of external Ca2+, since it occurred in Ca2+-free medium fortified with 2 mM EGTA. The Ca2+ imaging was well correlated with ion current measurements of voltage-clamped oocytes. Imaging, in addition to detecting the spatial spread of Ca2+ across the cell, was at least as sensitive as voltage clamping and much faster when screening oocytes for the expression of receptor mRNAs that stimulate Ca2+ mobilization. While it is known that fertilization of Xenopus eggs causes a spreading wave of Ca2+ mobilization, we found that activation of either native or newly expressed receptors in oocytes causes a similar change in Ca2+ distribution.
Proceedings of the National Academy of Sciences of the United States of America © 1990 National Academy of Sciences