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First published online April 18, 2008
Journal of Experimental Biology 211, 1394-1401 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.014282

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Is there life in the horny layer? Dihydropyridine and ryanodine receptors in the skin of female and male chickens (Gallus domesticus)

Liisa M. Peltonen^1,* and Satu Mänttäri²

¹ Department of Biomedicine/Physiology, Biomedicum Helsinki, PO Box 63, 00014 University of Helsinki, Finland
² Department of Biology, PO Box 3000, 90014 University of Oulu, Finland

^* Author for correspondence (e-mail: liisa.m.peltonen{at}helsinki.fi)

Accepted 18 February 2008

Previous findings in pigeons and chickens show that Ca²⁺ may be accumulated inside the cornified skin cells and that Ca²⁺ microenvironments with a lower- or higher-than-blood concentration may exist in the skin. It has been suggested that the skin may function as a secretory pathway or a reservoir for Ca²⁺ recycling. To test this hypothesis, we studied the dermis and epidermis of female and male chickens in vivo to find out whether cellular mechanisms exist for the accumulation, recycling or secretion of Ca²⁺. For calcium influx and intracellular Ca²⁺ release, respectively, the density of dihydropyridine receptors (DHPRs) and ryanodine receptors (RyRs) was examined, using high-affinity (–)-enantiomers of dihydropyridine and ryanodine labelled with fluorophores. To investigate Ca²⁺ utilization in the skin, the systemic and local activity of the enzyme alkaline phosphatase (ALP) and the concentration of ionic Ca²⁺ were measured in plasma and in cutaneous extracellular fluid, collected by suction blister technique. We found that both DHPRs and RyRs were present in all skin layers from dermis to horny layer. However, receptor densities were highest in the surface layers. With a basic calcium-rich diet, receptor densities were higher in males, particularly in the dermis and mid-epidermis. After a reduction in the nutritional Ca²⁺ input, receptor densities in males decreased to the same level as in females, in which the receptor densities were not affected by the amount of Ca²⁺ in the diet or that resulting from coming out of lay. The extracellular concentration of ionic Ca²⁺ per se was not found to affect the density of DHPRs and RyRs in the skin. Spatially, RyRs seem to be located in the periphery of the sebokeratinocyte. ALP activity was shown to be lower in the extracellular fluid than in the plasma in both sexes. However, activity in both extracellular domains increased significantly in females that had come out of lay. This was probably connected with the increased osteoblast activity related to the reformation of structural bone. In conclusion, voltage-sensitive L-type Ca²⁺ channels for ion influx and RyRs for Ca²⁺ release are present in the cells of the skin of female and male chickens. Higher densities in the males receiving excessive Ca²⁺ imply an increased capacity for Ca²⁺ influx and intracellular processing. Even though the functional interactions between DHPRs and RyRs in the sebokeratinocytes could not be demonstrated, peripheral colocation and high receptor densities at the level of exocytosis of the lamellar bodies point to their role as part of a signalling pathway for secretion. The finding that DHPRs and RyRs are present in the horny layer implies that the function of the outermost skin might be more active than had been previously thought and that this function might be both secretory and sensory.

Key words: DHPR, RyR, calcium, skin, avian