MYOENDOCRINE-LIKE CELLS IN INVERTEBRATES - OCCURRENCE OF NONCARDIAC STRIATED SECRETORY-LIKE MYOCYTES IN THE GUT OF THE ANT FORMICA-POLYCTENA

The occurrence of myoendocrine-like cells investing the ampullar drain ing region of Malpighian tubules and neighboring midgut and hindgut re gions of the ant Formica polyctena is reported. These striated muscle cells show small electron-dense endocrine-like granules (130 +/- 0.95 nm) in addition to myofilaments and ordinary organules of the myocytes . Apart from their contractile function, such ultrastructural features suggest a regulatory role for these cells, as is the case of vertebra te myoendocrine cells. As far as we know, the ant secretory myocytes r eported here constitute the first description of myoendocrine cells am ong invertebrates, as well as the first report of secretory, striated muscle cells outside the heart in the animal kingdom. (C) 1994 Academi c Press, Inc.