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This review addresses the role of lipids and membranes in biologic calcification and examines their regulation during endochondral ossification. The close association of lipids with mineral deposition has been well established. Early observations indicated that lipids, particularly phospholipids, can not be totally extracted from calcified tissues until the tissues are decalcified. Phospholipids associated with mineral are also enriched in extracellular membrane vesicles, called matrix vesicles. Numerous studies indicate that mineral deposits in calcifying cartilage are first seen in these phosphatidylserine and alkaline phosphatase enriched vesicles and that the process of endochondral calcification of epiphyseal growth plate is possibly mediated by them. Matrix vesicles, and the phospholipids present in them, appear to be involved in initial formation of calcium hydroxyapatite crystals via the interaction of calcium and phosphate ions with phosphatidylserine to form phospholipid:Ca:Pi complexes (CPLX). CPLX is present in tissues which are undergoing initial mineral deposition but are absent from nonmineralizing tissues. Evidence suggests that CPLX resides in the interior of matrix vesicles where the earliest mineral crystals are formed in association with the vesicle membrane. More recently, it has been determined that specific membrane proteins, called proteolipids, participate in CPLX formation and hydroxyapatite deposition, in part by structuring phosphatidylserine in an appropriate conformation. Phosphatidylserine involvement in the initiation of mineralization has been extensively investigated because of its extremely high binding affinity for Ca2+. In addition to structuring a specific phospholipid environment, proteolipids may also act as ionophores, promoting export of protons and import of calcium and phosphate, both requirements of biologic calcification.(ABSTRACT TRUNCATED AT 250 WORDS)
Anat Rec 1989 Jun
PMID:Role of lipids in calcification of cartilage. 267 85

The present paper reviews the use of liposomes as synthetic models for studying various biophysical aspects of matrix vesicle calcification, especially the involvement of acidic phospholipids in the nucleation and growth processes which occur during the initial stages of mineral formation in and around these membrane-bound structures. Recent results showed that acidic phospholipids incorporated into phosphatidylcholine-rich anionic liposome membranes were ineffective in initiating extraliposomal calcium phosphate precipitation from metastable solutions at physiological pH. On the contrary, certain acidic phospholipids such as phosphatidic acid and phosphatidylserine retarded the development of such precipitation when the latter was endogenously induced. The extent of inhibition correlated with the strength of the electrostatic interaction between the polar head group of the acidic phospholipid and the surface of the mineral phase. The results suggest that acidic phospholipids may play an important role in controlling the rate of early mineral development in matrix vesicle calcification.
Anat Rec 1989 Jun
PMID:Biophysical aspects of lipid interaction with mineral: liposome model studies. 267 86

Many studies of calcium phosphate precipitation have been made using relaxation techniques in which the concentrations of the lattice ions are allowed to decrease as equilibrium is approached. Since the nature of the phases that form depend markedly on the solution composition, this decrease can lead to concomitant phase transformations during the crystallization experiments. The results of the present constant composition (CC) studies show that defect apatites may be formed under conditions of sustained supersaturation with a non-stoichiometric coefficient dependent on the pH of the growth medium. An important factor in analyzing these experiments is the initial surface modification and ion-exchange processes involving H+ and Ca2+ ions after inoculation of the supersaturated solutions. Thereafter, active growth sites may be eliminated as the crystals undergo lattice perfection. Transformation of dicalcium phosphate dihydrate to octacalcium phosphate, involving dissolution and subsequent nucleation and growth of the new phase, is also influenced by surface roughening of the initial phase. Typical inhibitors that reduce the rate of growth of seed crystals in supersaturated solutions may actually induce the nucleation of calcium phosphate phases when immobilized on inert surfaces. This may be a factor in the modulation of crystal growth in many biological systems.
Anat Rec 1989 Jun
PMID:Mineral phases of calcium phosphate. 267 88

The application of high resolution electron microscopy, computer image processing, and image simulation techniques to the investigation of synthetic nonstoichiometric apatites has provided new details of apatite crystal growth mechanisms. Under certain precipitation conditions, calcium-deficient apatites with distinct octacalcium phosphate (OCP)-apatite intergrowths have been observed. Apatite crystals with unit-cell thick overgrowths of OCP on their surfaces confirmed the stepwise hydrolysis crystal growth mechanism initially proposed by Brown (Nature 196:1048-1050). However, many crystals also contained a central two-dimensional OCP inclusion one to two unit cells thick, embedded in an apatite matrix. Similar planar defects have been observed in dental enamel, dentin, and bone crystals. We have developed a modified version of Brown's stepwise OCP hydrolysis apatite crystal growth mechanism to explain the formation of crystals with OCP central planar defects. The mechanism involves the nucleation of an OCP seed that grows until it reaches a critical size, rh, before OCP hydrolysis occurs. Apatite subsequently grows epitaxially on the OCP seed, thereby embedding it in the center of an apatite crystal. Apatite growth is facilitated by partial screw dislocations emanating from the planar defect.
Anat Rec 1989 Jun
PMID:High resolution electron microscopy of nonstoichiometric apatite crystals. 267 90

To obtain bacterial-mediated oncogenic transformation of plants, the transferred DNA (T-DNA) of the tumor-inducing (Ti) plasmid of Agrobacterium tumefaciens is transferred to its plant host cells during infection. The initial phases of transformation involve the processing of the T-DNA in the bacterial cell after induction of the vir genes located on the Ti plasmid. The kinetics and conditions of this processing were examined and upon induction with acetosyringone up to 40% of the left and right borders of the T-DNA were cleaved. This cleavage was dependent upon virA, virG, and VirD and was rec-independent. Processed T-DNA was observed within 30 min after induction and was delayed by an increased concentration of phosphate in the induction medium. When DNA was isolated in the absence of protease treatment, the DNA fragment corresponding to the left side of the cut at both the left and right border region exhibited gel retardation, suggesting one or more "pilot" proteins may be involved in T-DNA transfer. Although the relative abundance of a processed product does not necessarily imply relative importance, the preponderance of double-stranded cleavage products suggests that double-stranded T-DNA should be considered as a possible intermediate in T-DNA transfer.
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PMID:High levels of double-stranded transferred DNA (T-DNA) processing from an intact nopaline Ti plasmid. 292 22

Fortnightly injections with 500 mg (1.4 ml) of recombinant bovine somatotrophin in 20 dairy cows and heifers at 80 +/- 7 days after calving resulted in increasing milk yields, compared with paired control cows, for three to four days. The advantage was maintained for a further seven to eight days with a decline occurring during the last two to three days before the next injection. The milk yield did not return to the level of the control cows, and the gap between the lactation curves widened as treatment continued, until two to three weeks after the last injection. The cows' response to treatment was greater than the response to heifers. Blood beta-hydroxybutyrate concentrations reflected the higher energy requirements of the treated animals and the weight loss of the treated heifers. Urea-nitrogen concentrations were significantly lower in the treated animals, suggesting that they utilised protein more efficiently. Treated animals had higher inorganic phosphate concentrations, although they remained within the normal ranges. Differences in calcium, magnesium, albumin and globulin concentrations were either statistically or practically not significant.
Vet Rec 1989 Jan 28
PMID:Milk production, weight changes and blood biochemical measurements in dairy cattle receiving recombinant bovine somatotropin. 292 83

The effect of a diabetogenic dose of streptozotocin on the secretory activity of ameloblasts was investigated in the rat incisor by radioautography. One group of male Sprague-Dawley rats was injected intravenously with streptozotocin in citrate buffer (pH 4.5). One hour later, this group was again injected intravenously with 3H-proline (2 mCi/kg). A control group of animals was injected with 3H-proline only. All the animals were sacrificed in groups of three at 5 min, 1 h, 2 h, 4 h and 8 h after 3H-proline injection by perfusion with 3% phosphate-buffered formaldehyde followed by an additional perfusion with 2.5% phosphate-buffered glutaraldehyde. The incisors were extracted with the jaws, demineralized, and prepared for radioautographic observations and analysis. The principal effects of streptozotocin were as follows: There was an inhibition of 3H-proline incorporation into the secretory ameloblasts at 5 min after injection. This was followed by a larger uptake and a slower passage of the label out of the cells into the enamel matrix than that seen in the control sample. Finally, there was a slower secretion of labeled proteins out of Tomes' processes between 1 and 4 h after injection. Therefore, streptozotocin had a temporary inhibitory effect on the incorporation and secretion of 3H-proline by the secretory ameloblasts of the rat incisor. This effect was present for about 4 h and was completely reversed 9 h after streptozotocin injection.
Anat Rec 1986 Jan
PMID:The effect of streptozotocin on the secretory activity of ameloblasts in rat incisor as revealed by radioautography after 3H-proline administration. 293 48

Transmission electron microscopy and ultracytochemistry were employed in an attempt to localize the enzyme calcium adenosine triphosphatase (Ca-ATPase) in the rod outer segments (ROS) of the toad retina. Utilizing a one-step incubation procedure, Ca-ATPase was identified as an electron-dense precipitate in the intradiskal spaces of the rod disks (vesicles) of the ROS. Analytical microscopy identified the reaction product as lead phosphate. The formation of the reaction product was dependent on the presence of ATP (the substrate) and calcium ions. However, calcium ions could be substituted for by magnesium ions. In addition, the reaction was vanadate sensitive. The latter is known to inhibit Ca-ATPase activity. Such data appear to indicate the presence of a Ca-Mg-ATPase in association with the rod disks. Since cyclic guanosine monophosphate (cyclic GMP), rather than calcium ions, is currently believed to be the primary intracellular messenger associated with phototransduction, the presence of an ROS Ca-ATPase may indicate other functions for this cation in the physiology and biochemistry of the visual process. Ca-ATPase might play a role in directional calcium fluxes between intracellular compartments.
Anat Rec 1988 Jul
PMID:Electron microscopic cytochemical localization of Ca-ATPase in the rod outer segments of the toad Bufo marinus. 297 64

The effects of starvation on glucose 6-phosphatase (G6Pase; EC 3.1.3.9., D-glucose 6-phosphate phosphohydrolase) and glycogen phosphorylase (EC 2.4.1.1.) activities, and on glycogen content, were studied in skeletal muscles (m. rectus femoris) of mice. In the muscle cells from fed animals, the cytochemical reaction product for G6Pase activity was observed in moderate amounts in the terminal cisternae of sarcoplasmic reticulum and in small amounts in the nuclear envelope, and was rare or absent in the intermyofibrillar sarcoplasmic reticulum. After 4 days of starvation, however, the reaction product became abundant in all of the terminal cisternae, intermyofibrillar sarcoplasmic reticulum, and nuclear envelope. Biochemical G6Pase and glycogen phosphorylase a (active form) activities were higher in the muscles of starved mice than in those of fed animals. The glycogen content decreased markedly in the muscles of starved mice. The results suggest that the role of the increased G6Pase in skeletal muscle cells of starved mice is to release glucose into the blood by hydrolyzing glucose 6-phosphate produced through the increased phosphorylase activity.
Anat Rec 1986 Oct
PMID:Significance of the increase in glucose 6-phosphatase activity in skeletal muscle cells of the mouse by starvation. 302 18

Haematological and blood biochemical changes were studied in nine camels after maximal exercise over 4 or 5 km. There was a lack of splenic reserve for red blood cells, indicated by a minimal increase in haemoglobin concentration and haematocrit. There were marked increases in plasma lactate (to over 20 mmol/litre), plasma ammonia and plasma glucose and a pronounced decrease in circulating free fatty acids. There were small but significant increases in plasma calcium, magnesium, sodium, potassium, chloride and phosphate concentrations.
Vet Rec 1988 Sep 17
PMID:Effects of maximal exercise on the blood composition of the racing camel. 319 11


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