Development Of Calcium Pools In Early Embryonic Chicken
Sean M. Mercer ('96), Jeffery D. Cromartie ('97), and A. Malcolm Campbell
Presented at the 10th National Conference on Undergraduate Research (NCUR - 10), April 18 - 20, 1996, UNC Asheville. (page PS2-1 of abstracts)
Calcium plays a critical role in cellular homeostasis, neurotransmitter release, and muscle contraction. Calcium pools consist of calcium ion pumps, channels, and buffers. Sarco/endoplasmic reticulum calcium ATPase (SERCA) is the transmembrane protein which actively transports calcium ions from the cytosol into the sarcoplasmic reticulum (SR) for storage, which permits muscle relaxation. The ryanodine receptor and the inositol 1,4,5,-trisphosphate (IP3) receptor are both calcium channels which allow calcium ions to be released from the SR. The early expression of the cardiac SERCA isoform (SERCA2) was examined in cardiac myocytes of chicken embryos (stages 10 -14) using indirect immunofluorescence labeling. Our results support the observations of Jorgenson and Bashir (Dev. Biol. 106: 156-165, 1984), which showed a gradient of SERCA2 expression, consistent with the anterior to posterior development of the embryo. However, immunofluorescence labeling of intact chicken embryos allowed us to observe a punctate expression pattern of SERCA2. A small cluster of cells began to express SERCA2 by late stage 10. This cluster increased in intensity of expression and number of cells during stage 11 to form a patch of cells. By mid-stage 11, the patch was located on the right margin of the ventricle and every cardiac myocyte expressed SERCA2 by stage 14. Our observations not only support an anterior to posterior gradient, but also suggest an additional gradient of SERCA2 expression in early chicken heart development. The stage 11 expression of SERCA2 along the right margin of the ventricular wall coincides with the location of the first visible contractions (Patten and Kramer Physiol. Rev. 29: 31-47, 1949). The punctate expression pattern of SERCA2 correlates with the initial pattern of cardiac myocyte contraction. However, neither the ryanodine receptor nor the IP3 receptor were detected in the first two days of embryonic development. Therefore, calcium pool development is incomplete by the end of embryonic day 2.
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