A physiological role for protoporphyrin IX photodynamic action in the rat Harderian gland?
OBJECTIVE
The lipid-secreting exocrine Harderian gland contains a large amount of porphyrins (mainly protoporphyrin IX, PPIX) in the glandular cells, the physiological significance of which is rather poorly understood.


METHODS
In the present study, the possibility of using Fura-2 to measure intracellular calcium ([Ca2+]c) changes in these cells was assessed.


RESULTS
It was found that when Fura-2-loaded cells were excited by light at 340/380 nm, [Ca2+]c increased spontaneously, indicating a photodynamic action powered by light at 340/380 nm. In contrast, with the visible spectrum calcium probe Fluo-3 (lambda(ex) = 475 nm), carbachol at 10 microm induced [Ca2+]c increase; [Ca2+]c did not change without carbachol stimulation. Brief illumination with light at 340/380 nm induced a large [Ca2+]c increase in Fluo-3-loaded cells. Photodynamic stimulation of [Ca2+]c increase was confirmed with an exogenous photosensitizer sulphonated aluminium phthalocyanine (SALPC) and visible light (>580 nm). The wavelength-dependence of the [Ca2+]c increase correlates well with the excitation spectrum of the isolated Harderian glandular cells.


CONCLUSIONS
These data suggest that PPIX present in rat Harderian glandular cells plays the role of a photosensitizer which upon activation by UVA and blue components of daylight and subsequent singlet oxygen generation, triggers [Ca2+]c increase and secretory response. The PPIX photodynamic action may also play a potential role in photic entrainment of the central circadian clock.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D018679:Cholinergic Agonists / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000378:metabolism; D006243:Harderian Gland / Q000187:drug effects / Q000502:physiology*; D007211:Indoles / Q000494:pharmacology; D008027:Light; D008297:Male; D009942:Organometallic Compounds / Q000494:pharmacology; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011524:Protoporphyrins / Q000494:pharmacology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014466:Ultraviolet Rays
D018679:Cholinergic Agonists; D005456:Fluorescent Dyes; D007211:Indoles; D009942:Organometallic Compounds; D017319:Photosensitizing Agents; D011524:Protoporphyrins; C060570:aluminum phthalocyanine; D002217:Carbachol; C028025:protoporphyrin IX; D002118:Calcium; D016257:Fura-2