CALCIUM-BINDING PROTEINS IN AVIAN HERBST AND GRANDRY SENSORY CORPUSCLES

Background: Calcium-binding proteins (Ca2+-BP) are involved in the homeostasis of intracellular calcium ions (Ca2+), which play a key role in electrogenesis, and therefore in somatosensory transduction, within sensory corpuscles, This study analyze the distribution of several Ca2+-BP in avian Herbst and Grandry sensory corpuscles. Methods: Specimens of beak skin and tongue from ducks and pigeons were studied immunohistochemically using antibodies against S100 protein (S100P), calretinin (CR) calbindin D-28K: (CB), and parvalbumin (PV), Moreover, neurofilament proteins (NFP) and neuron-specific enolase (NSE) were studied in parallel. Results: In Herbst corpuscles: 1) specific immunoreactivity (IR) for S100P was always observed labelling the inner-core cells and was also found in the capsule of duck Herbst corpuscles; 2) all the other investigated Ca2+ -BP were found primarily in the inner-core, without relevant species-specific differences, but also in the central axon and in the capsule (CB and PV). In Grandry corpuscles, the Grandry cells 1) can be subdivided on the basis of S100P IR; 2) displayed a strong CR IR, moderate PV IR, and weak CB IR; 3) were negative for NFP or NSE. On the other hand, the central axon of both kinds of sensory corpuscles showed NFP and NSE IR, and the intraepidermic Merkel-like cells were NFP IR. Conclusions: Present results provide evidence for the presence of several Ca2+-BP in two kinds of rapidly adapting avian sensory corpuscles, and also for the existence of species-specific differences in the localization of some of them. These findings suggest that Ca2+-BP may be involved in the maintenance of Ca2+ homeostasis in avian sensory corpuscles, and therefore in mechano-electric transduction. (C) 1995 Wiley-Liss, Inc.