Dense Cored Vesicles in SAI Merkel Cells and Their Role in Mechano-Electric Transduction

Abstract

The SAI (slowly-adapting type I) mammalian mechanoreceptor is a well characterised and distinctive cutaneous sensory receptor. In hairy skin of the cat it is present as a dome-like epidermal structure innervated by a myelinated afferent fibre that ends in expanded disk-like flattened terminals each of which is associated with a Merkel cell (Iggo and Muir, 1969). Several studies have reported that the normal high sensitivity of the receptor to mechanical stimulation and the characteristic irregularities of the afferent discharge during sustained activity is dependent on the presence of innervated Merkel cells (Brown and Iggo, 1963; Burgess and Horch, 1973). The actual role of the Merkel cells in the normal function of the SAI is not yet, however, established and views range from the suggestion that they are the actual mechanoelectric transducers (Iggo and Muir, 1969; Horch et al., 1974) to the opposite extreme that they can be removed without affecting the functional properties of the sensory Open image in new window Fig. 1 Merkel cell-neurite complex, showing high density of granular vesicles (G) in Merkel cell cytoplasm between the cell’s nucleus (N) and the expanded terminal of the nerve (NP). receptor (Diamond, pers. comm.) or at least that they are not the transducers (Gottschaldt and Vahle-Hinz, 1982).