The buffer capacity and buffer systems of human whole saliva measured without loss of CO2

The buffer capacity of unstimulated (UWS) and stimulated (SWS) whole-mouth saliva involves three major buffer systems. The aim was to determine the buffer capacity of UWS and SWS at specific pH in the interval from pH 7.5 down to pH 3.0. The contribution of each of the buffer systems was also determined under conditions resembling those in the mouth. UWS and SWS were collected from 20 healthy volunteers; the saliva was collected under paraffin oil in order to avoid loss of CO2. The buffer capacity of UWS and SWS in samples with and without bicarbonate (HCO3-) and CO2 were measured at various pH by acid titration in a closed system at 36 C. The mean concentrations of the buffer systems in UWS (mean flow rate 0.55 ml/min) were 4.4 mmol/l HCO3-, 4.5 mmol/l phosphate (of which 1.3 mmol/l was present in the form of HPO4(2-)), 1876 microg/ml protein; the saliva pH was 6.8 and the P(CO2) 29.3 mmHg. The corresponding mean concentrations in SWS (mean flow rate 1.66 ml/min) were 9.7 mmol/l HCO3-, 3.8 mmol/l phosphate (of which 1.9 mmol/l was present in the form of HPO4(2-)), 1955 microg/ml protein; pH 7.2 and P(CO2) 25.7 mmHg, The highest buffer capacity of UWS and SWS was 6.0 and 8.5 mmol H+ /(1 saliva*pH unit) at pH 6.25, respectively. At saliva pH in the range from pH 7 down to pH 5, the following had significant impact on buffer capacity: the HCO3- concentration (p < 0.001), the flow rate (p < 0.01), and the pH of the saliva (p < 0.05). At acidic pH in the range from pH 5 down to pH 4, however, only the protein concentration had a significant impact on buffer capacity (p < 0.01).     

The flow-rate-dependent excretion of ionized calcium in human parotid saliva.

The total calcium content of parotid saliva is increased in various diseases. Because of methodological difficulties, little is known about the ionized calcium fraction although it might be of importance for the secretion of fluid and proteins. Using a new method with calcium-selective disc electrodes, which gives an easy and exact estimation of ionized calcium, the Ca²⁺ activity in pilocarpine-stimulated parotid saliva of 10 healthy males was measured. With increasing flow-rate (0.1–0.6 ml/min), the concentration of ionized calcium rose exponentially from 1.13 ± 0.36 mequiv./litre (0.57 ± 0.18 mmol/litre) to 1.76 ± 0.21 mequiv./litre. At higher flow-rates (up to 2.5 ml/min), a plateau was observed. The total calcium concentration and the ionic calcium concentration were closely correlated (r = 0.93) and the ratio ionic/total remained nearly constant at 0.54 at all flow-rates.     

The inhibition of acid production in human saliva by monofluorophosphate.

Sodium monofluorophosphate (MFP) and NaF were compared for their ability to inhibit acid production in human saliva-glucose mixtures. Whole stimulated saliva was incubated at 37 °C with 2.5 per cent glucose in the presence of NaF (1.05 mmol/l) or MFP (initially 1.05 mmol/1 or neither (controls). Because MFP was gradually decomposed, releasing fluoride, further incubations were included in which increments of NaF were added to reproduce this increasing fluoride concentration. Acid production in the MFP incubations was less than in the controls and greater than in those containing equimolar NaF, but almost the same as in those in which added fluoride reproduced the release from MFP. This showed that the inhibition of acid production in the MFP incubations was due to the fluoride released and that the PO₃F^2? ion itself had little or no effect. The hydrolysis of MFP by salivary enzymes was greater at pH 7 than at pH 4. A direct effect on plaque microorganisms by MFP is an unlikely explanation for the cariostatic properties of MFP toothpastes.     

The effects of extracellular citric acid acidosis on the viability, cellular adhesion capacity and protein synthesis of cultured human gingival fibroblasts

Root surface demineralization is widely used as an adjunct to periodontal treatment. To clarify the influence of citric acid root conditioning on periodontal wound healing, the effects of citric acid and associated extracellular acidosis on the viability (MTT assay), attachment and protein synthesis ([3H]-proline incorporation into trichloroacetic acid-precipitated proteins) of human gingival fibroblasts (GF) were investigated. A concentration of 47.6 mmol/L of citric acid (pH 2.3) in water led to total cell death within three minutes of incubation. Media containing 23.8 mmol/L and 47.6 mmol/L of citric acid exerted strong cytotoxicity (47 to 90 per cent of cell death) and inhibited protein synthesis (IC50 = 0.28 per cent) of GF within three hours of incubation. Incubation of cells in a medium containing 11.9 mmol/L of citric acid also suppressed the attachment and spreading of fibroblasts on culture plates and Type I collagen, with 58 per cent and 22 per cent of inhibition, respectively. Culture medium supplemented with 11.9, 23.8 and 47.6 mmol/L of citric acid also led to extracellular acidosis by decreasing the pH value from 7.5 to 6.3, 5.2 and 3.8, respectively. In addition, it was confirmed that the toxic effect of media containing citric acid was due to their acidity rather than the citrate content. Most of the citric acid-induced cell death could be prevented by adjusting the pH value of the culture medium to pH 7.5. Sodium citrate, at a concentration of 47.6 mmol/L, also exerted little cytotoxicity. The results suggested that toxicity of citric acid in specific stages of the healing process must be considered prior to its clinical application. Careful management of citric acid in order to avoid contact with tissue or the development of other demineralizing agents is important in enhancing periodontal wound healing.     

The state of calcium and inorganic orthophosphate in human saliva

The state of calcium and inorganic orthophosphate was investigated in resting parotid saliva and in stimulated parotid, submaxillary and whole saliva. Macromolecular binding was determined utilizing ultrafiltration procedures. Ionized calcium and phosphate in the ultrafiltrates were calculated on the basis of chemical analyses and considering the formation of the ion pairs CaHPO₄^o, CaH₂PO₄⁺ and CaHCO₃⁺. Mean findings showed that 85 per cent of the calcium in resting parotid saliva was ionized, while 8 per cent was bound to macromolecules and 6 per cent in ion pairs. In stimulated secretions, the ionized calcium ranged from 45 per cent (submaxillary saliva) to 54 per cent (mixed whole saliva) of total calcium. The macromolecular bound fraction accounted for 30–43 per cent while ion pairs bound 12–17 per cent of the calcium. Mean concentrations of ionized calcium were 0.74, 0.49, 0.76 and 0.59 mM respectively for the four types of saliva. Ultrafiltrability of inorganic orthophosphate ranged from 66 to 70 per cent in stimulated salivas and was over 90 per cent in resting parotid saliva. The ultrafiltrable phosphate was almost fully ionized because only 1–2 per cent was complexed with calcium. Mean concentrations of ionized orthophosphate were 6.58,2.59,2.08 and 2.53 mM respectively for the four types of saliva.     

The effects of different foods and concentrations of citric acid on the flow rate of whole saliva in man

The effects of seven different foods and three concentrations of citric acid in 16 adult subjects of each sex were evaluated. The foods were steamed rice, french fries, cheeseburger, cookie, milk chocolate, apple, and rhubarb pie. The volume of saliva was determined by subtracting the initial weight of food from that of the food bolus after subjects had chewed it normally and then spat it into a weighed container, without swallowing. The flow rates were compared with those produced in response to infusion into the mouth of 52, 156 and 260 mmol/l citric acid through a plastic tube at a constant rate of 5.0 ml/min, controlled by a peristaltic pump. Mean salivary flow rates were highest with rhubarb pie and lowest with rice; these were 70.5 +/- 11.3 and 43.2 +/- 14.4 per cent, respectively, of the maximum flow rate (7.07 +/- 2.16 ml/min) elicited by 260 mmol/l (5 per cent) citric acid. The chewing times per 10 g of food were inversely related to the water content (r = -0.82). The water content of the food bolus varied over a wide range (28-87 per cent). Thus normal foods elicit a salivary flow rate which is a high fraction of the maximum secretory rate achieved in response to acid.     

Retention of chlorhexidine in the human oral cavity after mouth rinses

The retention of chlorhexidine after mouth rinses was measured by the use of [¹⁴C]-chlorhexidine. The fraction swallowed was estimated using [⁵¹Cr]-EDTA. The mean total retention after 0.2 per cent chlorhexidine-digluconate mouth rinses (10 ml for 1 min) averaged 34 ± 7 per cent (6.9 ± 1.4 mg), and the oral retention 30 ± 7 per cent (6.0 ± 1.5 mg).The intra-individual variation, estimated by five mouth rinses at 1-week intervals, averaged ±4 per cent.The ¹⁴C-activity in saliva showed a sharp fall during the first few hours, followed by a slow release, with activity still present after 24 hr.     

The flow-rate-dependent excretion of ionized calcium in pilocarpine-stimulated human submandibular saliva

In 10 healthy male subjects the total calcium concentration in submandibular saliva varied between 2.05 +/- 0.12 mmol/l and 2.48 +/- 0.1 mmol/min, and did not show a dependency on the flow rate. The salivary-ionized calcium increased significantly at flow rates between 0.1 and 1.3 ml/min (from 0.74 +/- 0.05 to 1.41 +/- 0.04 mmol/l) and even reached plasma levels.     

Differences in basic proline-rich proteins in rat parotid saliva following chronic isoproterenol treatment or maintenance on a liquid diet

The basic proline-rich proteins (BPRP) in the stimulated parotid saliva of rats treated for 8 days with isoproterenol and rats fed a liquid diet for 2 weeks were compared to those in the stimulated parotid saliva of untreated rats fed a stock pelleted-diet (control). In the control, the BPRP were separated into 5 groups designated Peak A (the basic proline-rich glycoprotein), SP-1, SP-2, SP-3 and SP-4. The percentage of BPRP in each group was as follows: Peak A, 6.5 per cent; SP-1, 37 per cent; SP-2, 6.5 per cent; SP-3, 32.4 per cent; SP-4, 17.6 per cent. In the parotid saliva of rats fed the liquid diet, proteins corresponding to Peak A and SP-2 were not present, the proportion of BPRP in SP-4 was increased to almost 90 per cent while the proportions of material in SP-1 and SP-3 were reduced to 3 and 8 per cent, respectively. In the saliva of rats subjected to chronic isoproterenol treatment, a protein corresponding to SP-4 was not present; proteins corresponding to Peak A, SP-1 and SP-3 were present and in amounts similar to their proportion in untreated rats although material in SP-2 increased to 36 per cent.     

The effect of beta-sympathomimetic stimulation on parotid salivation in the red kangaroo (Macropus rufus)

Salivation was stimulated by intracarotid isoprenaline infusion given alone or combined with acetylcholine. By itself, isoprenaline (0.12-1.2 nmol kg-1 min-1) stimulated flow rates of 0.037-0.233 ml min-1 (2.77-10.5 microliters/g gland per min). Salivary Na, Cl, PO4 and total solute concentrations were positively correlated with flow; K, Mg and urea were negatively correlated with flow; and Ca, H+, HCO3, protein and amylase activity were not correlated with flow. Relative to cholinergic saliva, isoprenaline-evoked saliva had higher levels of amylase activity, urea, protein, K, Mg, H+, PO4 and Cl but lower osmolality, Na, Ca and HCO3. At a steady flow (1 ml min-1), isoprenaline infusion (0.3 nmol kg-1 min-1) superimposed on a pre-existing acetylcholine infusion increased salivary amylase activity, protein, urea, K, Mg, Cl and PO4, reduced HCO3 and did not alter Na, Ca, H+ and osmolality. Superimposition of isoprenaline infusion (0.5 nmol kg-1 min-1) on a low-level acetylcholine infusion increased flow rate by 400-900%. Excretion rates of K, Mg, Cl and PO4 were higher and Ca lower than predicted for saliva secreted at equivalent flows during acetylcholine stimulation. Na, H+ and HCO3 were as predicted for the same flow rate under cholinergic stimulation. The simplest coherent interpretation of these data is that isoprenaline affects transport of protein and ions at the end organs, but has little effect on the resting transport characteristics of the striated and excretory ducts of the kangaroo parotid, in accord with the known nerve distribution of this gland.     

Accumulation of enamel constituents in Streptococcus mutans plaque during intraoral demineralization

Studies were carried out with an intraoral demineralizing system in order to determine whether calcium and inorganic phosphate (Pi) accumulate in plaque during active demineralization of enamel. Blocks of bovine enamel were coated with Streptococcus mutans and were carried in palatal appliances worn by human volunteers. Demineralization was determined as changes in the iodide penetrability (delta Ip) of the enamel surfaces. Ca and Pi were determined in the extracellular spaces of the synthetic plaque. Delta Ip increased with time after administration of rinses containing 5% (w/v) sucrose, while plaque pH dropped and then returned toward neutrality. Ca increased to 10.9 +/- 2.8 mmol/l at 30 min, while Ca2+ and Pi rose to 3.0 +/- 2.1 and 9.5 +/- 3.1 mmol/l, respectively. The Ca:Pi ratio was 1.15. Rinses with 10% (w/v) sucrose gave similar results. Concentrations of Ca and Pi were considerably higher than those in saliva. Accumulation of the mineral constituents was shown to be dependent on metabolic activity of the S. mutans plaque, and experiments in which enamel blocks were replaced with blocks made of acrylic plastic gave Ca and Pi concentrations of 2.5 +/- 0.6 and 6.6 +/- 2.4 mmol/l, respectively, demonstrating that most of the Ca and about one-third of the Pi were derived from enamel. The data suggested, furthermore, that Ca and Pi were partially bound to complex macromolecules, and that part eventually recrystallized as mineral within the plaque.     

Circadian rhythms in the flow rate and proportional contribution of parotid to whole saliva volume in man

Seven subjects collected both left-parotid saliva and the remaining whole saliva simultaneously under resting conditions and under“sour-lemon-drop” (SLD) stimulation at five different times each day for spans of 11–17 consecutive days. Leastsquares cosine analysis of the data demonstrated statistically significant circadian rhythms under resting conditions in the estimated flow rates from both parotid glands (mean level, 0.13 ± 0.02 ml/min; amplitude, 0.05± 0.01 ml/min; acrophase, ?234.1 ± 5.0 ° [i.e. 3.36 p.m.± 20min.]), and in the flow rate of whole saliva (mean level, 0.46 ±0.05 ml/min; amplitude, 0.15 ± 0.03 ml/min; acrophase, ?250.2 ± 5.9 °) as well as in the parotid contribution to whole saliva volume (mean level, 28.4± 3.6 per cent; amplitude, 3.5±0.4 per cent; acrophase, ?165.9± 19.2 °). Under SLD-stimulation in which the left parotid flow rate was maintained constant at 1 ml/min, statistically significant circadian rhythms could not be demonstrated in the flow rate of whole saliva or in the proportional contribution of parotid to whole saliva.     

The composition of unstimulated whole saliva of healthy dental students

The purpose of this study was to determine the unstimulated whole saliva biochemical parameters in healthy dental students of Tehran University of Medical Sciences (TUMS) living in the students' dormitory with a mean age of 22 years. Five ml whole saliva samples were obtained by expectoration. The saliva composition was measured by a spectrophotometer and affiliated kits. The data was analyzed through the student's unpaired t-test using the SPSS program. In the male students (n=50) the mean concentrations of glucose (mmol/l), inorganic phosphate (mmol/l), total protein (mg/ml), magnesium (mmol/l), chloride (mmol/l), and calcium (mmol/l) were 0.75+/-0.44, 1.52+/-0.63, 6.69+/-2.89, 1.27+/-0.45, 27.60+/-11.06, and 2.17+/-0.76, respectively. In the female students (n=50) they were 0.73+/-0.47, 1.58+/-0.63, 7.26+/-3.78, 1.37+/-0.44, 30.42+/-12.74, and 1.87+/-0.78, respectively. There were no significant differences between the whole saliva values in male and female students.     

Effects of salivary bicarbonate content and film velocity on pH changes in an artificial plaque containing Streptococcus oralis, after exposure to sucrose

Chewing-gum stimulation of salivary flow (at the time of the pH minimum following exposure of plaque to carbohydrate) has been shown to cause a rapid increase in plaque pH. The objective of this study was to determine whether the rise in plaque pH is primarily due to the increased buffering capacity of stimulated saliva, or to the fact that an increased flow rate increases the concentration gradient for acid to diffuse from the plaque into the overlying salivary film, which will be moving at a higher velocity. This was investigated with an in vitro technique in which artificial plaque (0.5 or 1.5 mm deep) containing S. oralis cells was exposed to 10% sucrose for one min. The pH values at the proximal and distal undersurfaces of the plaque were then monitored during the passage of a 0.1-mm-thick film of a sucrose-free artificial saliva over the surface, at a range of film velocities (0.8-8 mm/min) that have been estimated to occur in vivo. When a minimum plaque pH had been achieved, the salivary film velocity was either (a) kept the same, with or without 15 mmol/L HCO3 (the concentration measured in chewing-gum-stimulated saliva), (b) increased to 86.2 mm/min, or (c) increased to 86.2 mm/min with 15 mmol/L HCO3 added to the artificial saliva. The findings suggest that after sucrose ingestion, the rapid rise from minimum plaque pH values, which can occur with gum-chewing stimulation of salivary flow, is due to the combined effects of the increase in salivary film velocity, and of a greater availability of bicarbonate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Salivary secretion induced from isolated, perfused rat submandibular glands by sympathomimetic agents

Saliva secretion was elicited from the isolated preparations by isoproterenol and phenyl-ephrine, at concentrations from 10⁻⁸ to 10⁻⁵ M. The volumes of saliva secreted during a 60-min period, the rates of flow and the electrolyte composition of saliva secreted in response to each secretagogue were similar to those in vivo. Replacement of perfusate Na⁺ inhibited the secretion of fluid induced by isoproterenol (75 per cent) and by phenylephrine (99 per cent). It also reduced the Na⁺ and K⁺ concentrations of saliva elicited by the two secretagogues and inhibited isoproterenol-induced protein secretion (81 per cent). Omission of Ca²⁺ from the perfusate also inhibited fluid secretion (isoproterenol-stimulated, 84 per cent; phenylephrine-stimulated, 99 per cent) and isoproterenol-induced protein secretion (69 per cent). The absence of the divalent cation in the perfusate resulted in increased Na⁺ and decreased K⁺ concentrations in isoproterenol-stimulated saliva and in reduced K⁺ concentrations in phenylephrine-stimulated saliva. Administration of 10⁻⁵M phentolamine did not modify the volume of saliva secreted in response to isoproterenol, but reduced the response to phenylephrine by 90 per cent. The antagonist caused some reduction in the Na⁺ and K⁺ concentrations of isoproterenol-stimulated saliva, but did not modify those of phenylephrine-evoked secretion. Little recovery in fluid secretion was observed when the isolated gland was perfused with complete perfusate in the presence of phenylephrine after perfusion with Na⁺- or Ca²⁺-free solutions. Thus perfused rat submandibular glands are fully functional preparations, which respond to sympathomimetic agents of the and β types. Both external Na⁺ and Ca²⁺ are required for fluid secretion with either type of stimulus, a finding which suggests that a similar ionic mechanism, involving an influx or mobilization of Ca²⁺ and Na⁺, is activated for the secretion of saliva when either or β adrenergic receptors are stimulated by appropriate agonists.     

Relationships between medication intake, complaints of dry mouth, salivary flow rate and composition, and the rate of tooth demineralization in situ

The aim of this study was to describe the relationships between the rate of tooth demineralisation and medication intake, subjective feeling of dry mouth, saliva flow, saliva composition and the salivary level of lactobacilli. The study group consisted of 28 subjects that were divided into three groups according to their unstimulated whole saliva flow rate. Group 1 had an unstimulated saliva low rate < or =0.16 ml/min (n=10), group 2 had one from 0.17--0.30 ml/min (n=9), and group 3 had one >0.30 ml/min (n=9). The rate of tooth demineralization was determined as mineral loss assessed by quantitative microradiography of human root surfaces, exposed to the oral environment for 62 days in situ. The unstimulated and stimulated saliva flow rates, pH, bicarbonate, calcium, phosphate, and protein concentrations, as well as the degree of saturation of saliva with hydroxyapatite and the saliva buffer capacity were determined. The results showed that almost all subjects developed demineralization, albeit at highly varying rates. Eighty-five percent of the subjects in group 1, 33% of the subjects in group 2, and 0% of the subjects in group 3 developed mineral loss above the mean mineral loss for all the root surfaces in this experiment. Futhermore, group 1 differed significantly from groups 2 and 3 in having a higher medication intake, a more pronounced feeling of dry mouth, lower stimulated saliva flow rate, lower stimulated bicarbonate concentration, lower unstimulated and stimulated compositional outputs (bicarbonate, calcium, phosphate, and protein), and a higher Lactobacillus level. The best explanatory variable for high mineral loss in this study was a low unstimulated saliva flow rate. In conclusion, our results suggest that an unstimulated salivary flow rate < or =0.16 ml/min as described by Navazesh et al. (1992), is a better indicator of increased caries risk due to impaired salivation, than the currently accepted definition of hyposalivation (unstimulated saliva flow rate < or =0.10 ml/min), which relates to the function of the salivary glands (Sreebny, 1992).     

Salivary conditions and cariogenic microorganisms in 55, 65, and 75-year-old Swedish individuals

Abstract – Secretion rate, buffer capacity, and cariogenic microorganisms of resting and stimulated whole saliva were examined in 208 55-, 65-, and 75-yr-old Swedes. The secretion rate for both resting and stimulated saliva decreased with age. When the use of drugs was taken into account the difference in terms of age group was significant for resting saliva alone (P<0.01). In 22%, the resting saliva was <0.1 ml/min, and in 5% the stimulated saliva was <0.7 ml/min. Persons with subjective dryness in the mouth had a lower salivary flow. Men had higher secretion rates than women irrespective of medication (P<0.05). The buffer capacity was strongly correlated to the secretion rate of both resting and stimulated saliva (r=0.39 and r=0.44, respectively). The number of mutans streptococci and lactobacilli increased with age, although significant in terms of age group for lactobacilli alone (P<0.05). The number of these microorganisms was lower in resting saliva than in stimulated saliva (P<0.0001). Individuals harboring both Streptococcus mutans and Streptococcus sobrinus had higher values of mutans streptococci in resting and stimulated saliva than those harboring only S. mutans (P<0.001). Actinomyces viscosus and Actinomyces naeslundii comprised 1% of the total CFU in 89% of the plaque samples. The corresponding figures for lactobacilli and mutans streptococci were 6% and 38%, respectively.     

Effects of an experimental diet on parotid saliva and dental plaque pH in institutionalized children

Sixty-six children aged 6-12, permanent residents of a children's home, were placed on a diet during a 45-day experimental period to measure salivary flow-rate, pH of saliva and dental plaque, total concentrations of salivary proteins, inorganic phosphate, bicarbonate, calcium and amylase. The total caloric content, as well as the proportional nutrient and calorie distribution of the foods, were determined and compared with those of the previous habitual diet. After the experimental period, stimulated parotid salivary flow, increased by 40 per cent over the pre-experimental values. Total proteins of saliva and pH of both saliva and dental plaque increased significantly, whereas inorganic phosphate concentration decreased. Concentrations of bicarbonate, calcium and amylase did not differ from those found pre-experimentally. The findings appear to derive from lesser retention and increased hardness of the foods in the experimental diet.     

Isolation and characterization of the basic proline-rich proteins from rat parotid saliva

Five fractions of basic proline-rich proteins were isolated from rat parotid saliva, obtained by surgical cannulation of the ducts. The purification procedures employed DEAE-Sephadex to isolate a heterogeneous break-through fraction containing the basic proline-rich proteins, followed by gel filtration on Sephadex G-200 to separate the high molecular weight glycoprotein, fraction A, from the other basic proline-rich proteins which were resolved into four additional fractions, SP-1 to SP-4, by ion exchange chromatography on SP-Sephadex. The proteins differed in their amino acid composition and content of neutral and amino sugars. All the proteins were characterized by a high proportion of proline (approx. 40 mol per cent) and glycine (11–23 mol per cent). Four of the fractions were also enriched in glutamic $\text{acid}\text{glutamine}$ (19–26 mol per cent). The exception was fraction SP-4, which contained lower levels of glutamic $\text{acid}\text{glutamine}$ and has no counterpart in human basic proline-rich proteins. Fraction A, the basic glycoprotein, was heavily glycosylated (59 mol per cent), whereas SP-2 and SP-4 were less glycosylated. Fractions SP-1 and SP-3 contained low levels of neutral and amino sugars. Basic proline-rich proteins constitute a smaller percentage of the total protein in rat parotid saliva than they do in human parotid saliva (10.5 versus 40 per cent). Rat basic glycoprotein fraction constitutes less than 1 per cent whereas the human glycoprotein fraction constitutes 17 per cent. Rat basic proline-rich proteins appear to be larger and less basic than most of the human basic proteins, and they resolve into fewer protein fractions (4 versus 9) with SP-Sephadex chromatography.     

The CaATPase activity of rat-incisor odontoblast vesicles

An homogenate of rat incisor odontoblasts had Ca²⁺ and Mg²⁺ ATPase activity and suitable storage conditions kept it stable for several days. Over 90 per cent of the activity was retained in a vesicle-rich microsomal fraction that removed about 85 per cent of the total material from the homogenate. This fraction was further characterized: the resolved Ca²⁺-activated ATPase activity, above the basal MgATPase activity, was 0.30 μmol P₁/min-mg total protein, and 50 per cent activated at free [Ca²⁺] equal 0.8 μM. This calcium dependency is consistent with an intracellular Ca²⁺-regulated enzymatic activity. The calcium ionophore, A23187, had no measurable effect on the CaATPase activity, which suggests that the odontoblast vesicles do not concentrate Ca²⁺ in a lipid bilayer compartment. Direct measurement of the uptake of ⁴⁵Ca²⁺ by the filtration method and parallel measurements of CaATPase activity on the same preparations under identical conditions indicated that the odontoblastderived vesicles have a coupling ratio of 0.024 Ca²⁺/ATP. This low coupling ratio and the lack of detectable compartmentalization of calcium indicate that the CaATPase activity of the odontoblast microsomes is not associated with a calcium pump. The [Ca²⁺] dependence of the activity suggests the CaATPase is under intracellular Ca²⁺ control, but its function is unknown.