Cytochemical localization of calcium and Ca2+,Mg2(+)-adenosine triphosphatase in colchicine-altered rat incisor ameloblasts.

Abstract

Colchicine is known to affect secretory, transport, and degradative functions of ameloblasts. The effects of colchicine on membrane-associated calcium and Ca2+,Mg2(+)-ATPase in secretory and maturation ameloblasts were investigated cytochemically. The pyroantimonate (PPA) method was used for localizing calcium and a modified Wachstein-Meisel medium was used to localize Ca2+,Mg2(+)-ATPase. Sections representing secretory and early maturation stages were examined by transmission electron microscopy. Morphological changes induced by colchicine included dislocated organelles and other well-established reactions to such anti-microtubule drugs. Calcium pyroantimonate (Ca-PA) deposits in most ameloblast types were markedly reduced, with the greater reduction occurring in those cells more severely altered morphologically. However, the cell membranes of both control and experimental smooth-ended maturation ameloblasts were essentially devoid of Ca-PA. The normal distribution and intensity of Ca2+,Mg2(+)-ATPase was not affected by colchicine. Because the observed reduction of membrane-associated calcium is apparently not mediated by Ca2+,Mg2(+)-ATPase in this case, other aspects of the calcium regulating system of ameloblasts are apparently targeted by colchicine.

Reduced Protein Expression of the Na+/Ca2++K+-Exchanger (SLC24A4) in Apical Plasma Membranes of Maturation Ameloblasts of Fluorotic Mice

“…Radioautographic studies with 45 Ca 2+ [23] and ultrastructural detection of Ca 2+ antimonate precipitates in plasma membranes [8] presented evidence that RE ameloblasts but not SE ameloblasts actively transport Ca 2+ into the enamel space. In the ameloblast layer of non-fluorotic wild-type mice, narrow gaps of immunonegative staining for NCKX4 were noted similar as for AE2 [24], resembling groups of SE ameloblasts.…”

“…Reduced secretion of buffer by ameloblasts could explain why the acidic RE bands in fluorotic enamel are wider [3, 4]. Ultrastructural detection of pyroantimonate precipitable Ca 2+ in plasma membranes of ameloblasts suggested that secretory and RE ameloblasts but not SE ameloblasts transport Ca 2+ across their membranes [8]. Exposure to F reduces the number of pyroantimonate precipitable Ca 2+ in the intercellular space of secretory ameloblasts [9] suggesting that fluoride reduced Ca 2+ transport is one factor responsible for hypomineralization of fluorotic enamel.…”

Cellular and Chemical Events During Enamel Maturation

“…Numerous studies have indicated that Ca2+,Mg2+-ATPases are enriched along the apical plasma membranes of ruffle-ended, but not smooth-ended, ameloblasts (Crenshaw and Takano, 1982;Takano et al, 1986;Sasaki et al, 1987a;Sasaki and Garant, 1987;Salama et al, 1989a;Eisenmann et al, 1990Eisenmann et al, , 1992Borke et al, 1993;Takano, 1995;Zaki et al, 1996). These ATPases seem very sensitive to anti-microtubular agents, which upset both the apical distribution pattern of the enzymes and the normal 45Ca uptake patterns seen in enamel (Eisenmann et at., 1990(Eisenmann et at., , 1992.…”

“…These ATPases seem very sensitive to anti-microtubular agents, which upset both the apical distribution pattern of the enzymes and the normal 45Ca uptake patterns seen in enamel (Eisenmann et at., 1990(Eisenmann et at., , 1992. Most workers, therefore, favor the idea that, regardless of how calcium ions get to the apical membrane of the cell, the ruffle-ended ameloblasts actively pump the calcium ions out of the cell into enamel using membrane ATPases (Bawden, 1989;Zaki et al, 1996).…”

“…Theories about calcium ion transport in the enamel organ depend to a large extent on differences that have been found between ruffleended and smooth-ended ameloblasts relative to: (1) "tightness" of apical/basal junctional complexes (simple permeability barriers) (Garant, 1972;Kallenbach, 1980;Takano and Crenshaw, 1980;Ozawa, 1980, 1984;Takano et al, 1983;Garant et al, 1984b;losephsen, 1984;Goldberg and Sasaki, 1985;McKee et al, 1986;Takano, 1995); (2) surface distribution of plasma-membrane-associated Ca2+,Mg2+-ATPases (calcium pumps) (Crenshaw and Takano, 1982;Takano et al, 1986;Sasaki et al, 1987a;Sasaki and Garant, 1987;Salama et al, 1989a;Eisenmann et al, 1990Eisenmann et al, , 1992Borke et al, 1993;Takano, 1995;Zaki et al, 1996); (3) presence/absence and distribution of various high-and low-affinity calcium-binding proteins and lipids in the plasma membranes and cytoplasm (calcium sponges) (Reith, 1983;Bawden, 1989;Berdal etal., 1991a,b;Takano, 1992Takano, , 1995Davideau et al, 1993;Hotton et al, 1995;Hubbard, 1995Hubbard, , 1996; and (4) the existence of low calcium uptake areas in enamel at short intervals after the injection of 45Ca (apparent calcium barriers) Crenshaw and Takano, 1982;Takano et al, 1982b;Reith et at., 1984;McKee and Warshawsky, 1986b;Kawamoto and Shimizu, 1987…”