Atrial granular cells of the snail Achatina fulica release proteins into hemolymph after stimulation of the heart nerve
2009
SUMMARY The atrium of the gastropod mollusc Achatina fulica receives rich
innervation and contains numerous granular cells (GCs). We studied the atrial
innervation and discovered that axon profiles typical in appearance of
peptidergic neurons form close unspecialized membrane contacts with GCs. Then,
we investigated, at both morphological and biochemical levels, the effect of
electrical stimulation of the heart nerve on GCs of Achatina heart
perfused in situ . The ultrastructural study demonstrated changes in
granule morphology consistent with secretion. These events included alteration
of granule content, intracellular granule fusion and formation of complex
degranulation channels, within which the granule matrix solubilized. It was
shown that electrical stimulation resulted in a significant increase of the
total protein concentration in the perfusate. Furthermore, SDS-PAGE analysis
of the perfusate revealed three new proteins with molecular masses of 16, 22,
and 57 kDa. Affinity-purified polyclonal antibodies against the 16 kDa protein
were obtained; the whole-mount immunofluorescence technique revealed the
presence of this protein in the granules of atrial GCs. In GCs of the
stimulated atrium, a progressive loss of their granular content was observed.
The results suggest that the central nervous system can modulate the secretory
activity of the atrial GCs through non-synaptic pathways.
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