Postma M, Oberwinkler J, Stavenga D. Does Ca2+ reach millimolar concentrations after single photon absorption in Drosophila photoreceptor microvilli?. Biophys J. 1999;77:1811-23 pubmed
..These very high concentrations show that the microvilli of fly photoreceptors are unique structures in which the Ca2+ signaling is even more extreme than in calcium concentration microdomains very close to Ca2+ channels. ..