Salivary glands of the cockroach, Periplaneta americana: New data from light and electron microscopy

Abstract

We have reinvestigated the morphology of the salivary glands in the cockroach, Periplaneta americana, by light, electron, and confocal laser scanning microscopy. All secretory acini have a uniform structural layout. They consist of three cell types: peripheral cells, central cells, and duct cells. One pair of peripheral cells forms the base of each acinus. The central cells, arranged concentrically in a fourfold symmetry around the most proximal part of the acinar ducts, lie next downstream. In every acinus, duct cells accompany the central cells and form a thin sheet on the apical surface of the latter. This apical lining of the duct cells is regularly fenestrated, and the central cells secrete the contents of their secretory vesicles only through these openings into the lumen of the ducts. Peripheral cells and central cells are never in direct physical contact, because, apically, extensions of the inner acinar duct cells intervene between the cells. Basally, thin extensions of the basement membrane separate the cell types. We have found no morphological evidence for the existence of electrical coupling (gap junctions) between the saliva-producing cells. Our ultrastructural data support the view that the peripheral cells are responsible for water and electrolyte transport, whereas only central cells secrete the proteinaceous components of the saliva. We have found that the duct cells distal to the acini are also specialized for ion and water transport. They have a prominent basal labyrinth containing numerous mitochondria and a highly folded apical surface. The folded apical membrane surface is coated with electron-dense particles on its cytoplasmic side; these particles are probably portasomes. Our investigation provides morphological evidence that the duct cells distal to the secreting acini are able to modify primary saliva.

Characterisation of neurotransmitter-induced electrolyte transport in cockroach salivary glands by intracellular Ca2+, Na+ and pH measurements in duct cells

“…However, mechanosensitive flow sensors such as apical primary cilia or flow-induced circumferential stretch as shown in kidney (Liu et al, 2003;Wang, 2006) are unlikely. The cockroach salivary ducts are relatively inelastic due to a luminal cuticle and no cilia extend into the duct lumen (Just and Walz, 1994a). More complex signalling processes could be involved, since epithelial transport in glands has been shown to be influenced by certain agonists present in the luminal compartment (Forte and Currie, 1995;Sakairi et al, 1995;Leipziger, 2003;Novak, 2003).…”

“…Cockroach salivary glands are of the acinar type and consist of several cell types (Just and Walz, 1994a). Salivation is controlled by dopaminergic and serotonergic neurons (Baumann et al, 2002;Baumann et al, 2004).…”

Source, topography and excitatory effects of GABAergic innervation in cockroach salivary glands

“…Salivary glands of young male imagines were dissected in physiological saline (PS: 160 mmol l -1 NaCl, 10 mmol l -1 KCl, 2 mmol l -1 CaCl 2 , 2 mmol l -1 MgCl 2 , 10 mmol l -1 glucose, 10 mmol l -1 TRIS, pH 7.4) as described previously (Just and Walz, 1994).…”

“…2A presents a schematic view of the organization of the cockroach salivary gland complex (Just and Walz, 1994) in order to give the reader some landmarks. The paired salivary glands consist of many lobules, each with numerous secretory acini.…”

“…The salivary glands are composed of three main cell types with different functions (Just and Walz, 1994;Just and Walz, 1996): the grapelike acini consist of a pair of ion-secreting peripheral cells (P-cells) and several protein-secreting central cells (C-cells). The P-cells are innervated by both dopaminergic and serotonergic fibers, and are responsible for ion and water transport.…”