Department of Biological Sciences
East Tennessee State University
Box 70,703
Johnson City, TN 37614-0703
Phone: (423) 439-6922
Fax: (423) 439-5958
millerh@mail.etsu.edu
Using the Reverse Hemolytic Plaque Assay, which identifies individual hormone secreting cells, we have found that in the rat atria, about 50% of total atrial cells will secrete ANP under both basal and steroid stimulation. Within that secreting population, 33% appear to be cardiomyocytes that secrete ANP and 68% do not appear to synthesize the hormone, as determined by in-situ hybridization.
The situation changes drastically when cells from each atrial chamber are analyzed separately. In the right atrium, 25% of the cells secrete ANP under both basal and steroid stimulation. In the left atrium, the basal secreting population is 15% but after steroid treatment, a secreting population of 25% is detected. This result would imply that steroids are stimulating a group of non-secreting cells in the left atrium to become ANP secreting cells.
Recently, a protein has been identified in plants that is immunologically similar to animal ANP. We have found this protein in the root and stems of Geraniums and have recently isolated a partial cDNA from Geranium root using a degenerative primer based upon the human ANP sequence. This partial cDNA has been sequenced and we are isolating the full length cDNA using primers generated from this sequence. We are also screening a cDNA library from Arabidopsis root to isolate the corresponding Arabidopsis cDNA for this protein. Preliminary studies show that water stess may affect the expression of this protein in Geraniums, suggesting this protein, like its animal counterpart, may be involved in water/solute movement in plants.