Effects of osmotic changes and neurosecretory extracts on kidney ultrastructure in the freshwater pulmonate Helisoma

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Abstract
The ultrastructure of the heart and kidney, and the effects of media of different osmotic concentrations and of nervous tissue extracts, have been investigated in Helisoma duryi and H. trivolvis. The auricle and ventricle walls do not appear to be possible sites for urine formation. In the kidney sac, ferritin and carbon particles are retained by the basement membrane of the epithelium, whereas horseradish peroxidase passes through the basement membrane into the intercellular spaces 10 min after injection. Epithelial cells have deep basal membrane infoldings. Intercellular spaces and spaces in the infoldings are wide in snails kept in distilled water but narrow in snails kept in isosmotic saline. When kidney sacs from saline-acclimated snails were treated in vitro with visceral ganglion extract from snails kept in distilled water these spaces rapidly expanded. Visceral ganglion extract from snails kept in saline, or extracts of other ganglia, had no effect. It is suggested that urine formation occurs in the kidney sac, and that a factor (probably neurosecretory) from the visceral ganglion may act on kidney sac epithelium to alter the rate of filtration and fluid (prourine) transport.