High glucose‐6‐phosphatase activity in osteoblasts in the metaphysis of femur of growing rats

Abstract

Glucose-6-phosphatase (G6Pase) activity was examined cytochemically in the metaphysis of femurs of 3- and 7-day-old rats. G6Pase and hexokinase activities were also examined biochemically in the femur and tibia of 3-day-old animals. The reaction product for G6Pase activity was seen in the endoplasmic reticulum and nuclear envelope of all cell types composing the metaphysis. The amount of the reaction product was abundant in osteoblasts, moderate in osteocytes, and moderate to scarce in osteoclasts and capillary endothelial cells. Biochemical G6Pase activity in the bones was higher than that in the brain, submandibular gland, or pancreas of the animals. Hexokinase activity in the bones was not different from that in the submandibular gland, pancreas, or kidney. The activity ratio of G6Pase and hexokinase in the bones (0.603) was greater than that in the submandibular gland, pancreas, or brain and smaller than that in the kidney. Possible physiological significances of the higher G6Pase activity in osteoblasts are discussed.

Histochemical Studies of Lysosomal Forming System in Osteoclasts with Calcitonin Treatment: Acid Phosphatase and Glucose-6-Phosphatase.

“…On the basis of this hypothesis, detection of G6Pase activity in ER of osteoclasts may be useful, as well as ER tracer. Tokunaga et al [46] reported moderate to scarce G6Pase activity in the ER of osteoclasts, and we observed same activity in the ER of control osteoclasts. On the other hand, G6Pase activity as seen in the control osteoclasts was seen in the ER of CT-treated osteoclasts.…”

“…It is not, however, a conspicuous element in the cell, and the function of ER on bone resorption has not been known yet. Generally G6Pase has been well utilized as a marker enzyme of ER [17,25,42,46,47,50,51], and one of the main functions of the enzyme reported in previous studies is gluconeogenesis on phosphohydrolase activity [36]. It has been recognized that much ATP is utilized by ATPdriven proton pump on the lysosomal membrane to make lysosomal acidification [11,12,16,31,41,43,48].…”

Glucose‐6‐phosphatase activity of endoplasmic reticulum and Golgi apparatus in spermatocytes and spermatids of the rat: an electron microscopic cytochemical study

“…In spermatocytes, all ER cisternae displayed G6Pase activity similar to the ER reactivity observed in Leydig cells, Sertoli cells and other cell types [19,22,41]. In contrast, the ER of spermatids was not uniformly labeled with cerium since some of the ER cisternae distal to the Golgi apparatus were G6Pase-positive, while others were either slightly reactive or negative.…”

“…Indeed, the consistency of the results obtained in several successive experiments, the uniformity of the distribution of the fine cerium precipitate over ER cisternae and some Golgi elements as well as the absence of non-specific dusty cerium deposits over the nucleus and cytoplasm of the testicular cell argued in favor of using cerium ions as capture agents. In addition, the consistency of the G6Pase activity in acidic, neutral or slightly alkaline media minimized the possibility raised by Tokunaga et al [41] that the reactivity observed in the Golgi apparatus may be due to acid phosphatases, which are known to be present in the Golgi apparatus of spermatids in particular [4,38,39]. Recent results obtained by Luo et al [22] on the ultrastructural localization of various phosphatases in cells of the pineal gland also tend to validate the use of the cerium technique in the cytochemical localization of phosphatases.…”

“…The cytochemical detection of G6Pase has been used repeatedly as a marker of ER cisternae [19,40,41,43]. Lead nitrate, traditionally used as a capture agent, gave erratic results when applied to the testis.…”