Isolation of two isoforms of a 21,000-dalton Ca2+-binding protein of bovine brain

Using Ca2+-dependent hydrophobic interaction chromatography we have identified a novel bovine brain Ca2+-binding protein (CaBP) composed of 21 kDa and 23 kDa polypeptides. This calciprotein was further purified by heat-treatment in the presence of Ca2+ and ion-exchange chromatography. The isolated protein exhibits a number of properties in common with proteins belonging to the calmodulin family of CaBPs, including a Ca2+-dependent electrophoretic mobility shift on SDS-polyacrylamide gel electrophoresis, retention of the ability to bind 45Ca2+ after electrophoresis and Western blotting, and a high content of acidic amino acids. We have recently isolated and characterized a 21 kDa CaBP from bovine brain and conclude that the 21 kDa and 21/23 kDa CaBPs are isoforms since they have very similar U.V. absorption spectra and amino acid compositions, and polyclonal antibodies raised in rabbits against the 21 kDa CaBP cross-react to an identical degree with the 21/23 kDa CaBP as determined by the competitive enzyme-linked immunosorbent assay (ELISA). Both proteins contain carbohydrate, but they differ in the degree of glycosylation. Tissue distribution studies indicate the presence of both 21 kDa and 23 kDa Ca2+-binding polypeptides in bovine trachea, aorta, kidney, skeletal muscle and cardiac muscle, and chicken gizzard smooth muscle.

The establishment of a new biological assay system for simultaneous measurement of bone resorption and bone mineralization in organ cultures of chick embryonic femur

A biological assay system has been developed for the simultaneous measurement of bone resorption and bone mineralization. In this system we (1) used chick embryonic femur as the biological material because of the easy handling and easy specification of developmental stages compared with rat and mouse, (2) labeled bone with 45Ca in vitro, (3) calculated the biological half life (T1/2) of 45Ca incorporated into bone salts for quantitative estimation of the bone resorbing activity, and (4) investigated bone-mineralizing activity by determining the calcium content before and after cultivation. Eleven-day-old chick embryonic femur was labeled with 45Ca in a chemically defined medium in vitro and thereafter labeled bones were transferred to chase medium. T1/2 was calculated from the sequential release of the label into the medium from the cultured bone. No one heretofore had determined the T1/2 of Ca in bone salts. We first determined in this study that the T1/2 of Ca in the chick embryonic femur is about 50 h. The decrease in T1/2 by parathyroid hormone, prostaglandin E1 and E2 and lipopolysaccharide, well-known stimulators of bone resorption, showed that this system works well in terms of bone resorption. By using this system, we demonstrated that immunomodulators such as Bacillus Calmette Guerin and Corynebacterium paruvum stimulate bone resorption and therefore affect bone metabolism. On the contrary, sodium fluoride (NaF) and hydrocortisone increased T1/2, indicating that they inhibit bone resorption. These agents were also tested to determine if they would alter total calcium in the bone during cultivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Chondroitin sulfate-derivatized agarose beads: a new system for studying cation binding to glycosaminoglycans

Chondroitin sulfate (CS) has been covalently attached to aminoethyl-agarose beads in a carbodiimide-catalyzed reaction. In this process, an amide bond is formed between carboxylate groups on the glycosaminoglycan (GAG) and the primary amine groups of the beads. Under optimal conditions, up to 160 micrograms of CS is attached per milligram of beads. CS-agarose beads have been used to study Ca binding to GAGs. The beads are mixed with a solution containing CaCl2 and 45Ca and allowed to sediment under unit gravity. An aliquot of supernatant is then removed and 45Ca activity is determined to quantitate remaining (free) Ca. Using this system, it was shown that CS binds approximately 0.7 Ca/disaccharide unit at saturation. Under the conditions used, the apparent association constant (KA) is approximately 14 mM. In principle, this derivatization protocol may be used to attach any proteoglycan or GAG (except keratan sulfate) to an insoluble support. CS-agarose beads provide a rapid, simple, and relatively artifact-free system for studying cation-GAG interactions.

Calcium absorption and excretion in patients treated with verapamil

1. The effect of verapamil on the intestinal absorption of calcium was studied using a single isotope technique. Serum calcium and urinary excretion of calcium in the urine were followed in nine patients during treatment with verapamil for 2 months. 2. A dose of 80-120 mg (three times daily) resulted in a significant reduction of systolic and diastolic blood pressure. 3. There was no change in the intestinal calcium absorption (alpha) expressed as the fraction of given activity absorbed per hour (alpha = 0.82 +/- 0.19 vs alpha = 0.83 +/- 0.25; +/- s.d., NS) or of the excretion of calcium in urine (Ca/creatinine ratio 0.35 +/- 0.20 vs 0.31 +/- 0.33; NS). 4. Serum calcium was not significantly different before and during treatment (2.43 mmol l-1 +/- 0.10 vs 2.47 mmol l-1 +/- 0.14; NS). 5. This study demonstrates that verapamil, at doses recommended for clinical use, does not seem to affect the intestinal absorption of calcium, the serum calcium concentration or the excretion of calcium in urine.

Effect of guanosine triphosphate on the release of Ca2+ from intracellular store sites of saponin-treated human peripheral lymphocytes

The effects of guanosine triphosphate (GTP) on the release and uptake of Ca2+ in nonmitochondrial intracellular store sites of human peripheral lymphocytes were examined. GTP in the presence of 3% polyethylene glycol released Ca2+ from the intracellular store sites of lymphocytes in a dose-dependent manner, and the maximal release was obtained at 10 microM GTP. GDP and 5'-GMP also enhanced the release of Ca2+. On the other hand, Ca2+ uptake in the presence of oxalate by saponin-treated lymphocytes was stimulated by GTP and this stimulation was abolished when polyethylene glycol was concomitantly present. The dose dependence of the stimulated Ca2+ uptake by GTP was much the same as that of the Ca2+ released by GTP. These results indicate that GTP has an inherent activity to release Ca2+ as well as to stimulate the uptake of Ca2+ in nonmitochondrial intracellular store sites of saponin-treated lymphocytes. The stimulatory effect of polyethylene glycol on GTP-mediated Ca2+ release may occur by inhibiting functions of the Ca2+ pump.

Calcium supplements: anion effects

The effects on bone remodeling of two anions commonly associated with calcium in the food and supplement chain (carbonate and phosphate) were evaluated in a pilot study in eight normal premenopausal women. Each woman was studied twice under full metabolic balance controls, once before starting treatment and then a second time after 4 months of treatment with either sodium bicarbonate in a dose providing 3240 mg carbonate daily or a mixture of sodium and potassium phosphates, providing 1144 mg additional phosphorus daily. Intakes of calcium and protein remained approximately constant between studies. Remodeling was measured by paired studies of both whole body calcium kinetics and trans-ilial bone biopsies. The extra phosphate was almost completely absorbed and produced the expected decline in urine calcium. Both anions were associated with slight decreases in intestinal calcium absorption efficiency; however neither anion altered bone remodeling as measured either by radiocalcium kinetics or by histomorphometry. Since the anion doses we used were larger than the average woman is likely to receive from either food or supplement sources, we conclude that neither anion alters bone remodeling in humans to a clinically significant degree. Additionally these findings underscore the essential safety of increased phosphorus intakes and have relevance to the use of phosphate as a remodeling activator in the ADFR (coherence therapy) approach to treatment of osteoporosis.

Effect of endothelium and carbachol on alpha-adrenoceptor agonist stimulated uptake and efflux of 45Ca in rat isolated aorta

Preincubation with carbachol (10 microM) did not affect basal 45Ca accumulation by rat isolated aortic segments complete with endothelium, although 45Ca accumulation was enhanced by removal of endothelium. This confirms the observation that in the presence of endothelium Ca2+ influx in rat aorta is antagonized, and indicates that the basal release of an endothelial derived factor might be sufficient to maximally antagonize basal Ca2+ influx, or alternatively that EDRF released as a result of muscarinic stimulation does not have identical effects to the factor released under basal conditions. Accumulation of 45Ca stimulated by B-HT 920 but not that stimulated by phenylephrine was antagonized in the presence of endothelium. Contractions elicited by B-HT 920 were abolished in the presence of endothelium while contractions evoked by phenylephrine were reduced by about 50%. Preincubation with 10 microM carbachol antagonized both phenylephrine (1 microM) stimulated 45Ca accumulation and contractile responses in the presence of endothelium to about the same extent. Therefore, it might be concluded that the inhibitory effect of EDRF in this tissue is due to an inhibition of stimulated Ca2+ influx. However, while addition of carbachol to tissues precontracted with phenylephrine elicited an immediate relaxation in the presence of endothelium, this relaxation could not be correlated with a reduction in tissue accumulation of 45Ca. Carbachol also antagonized the phenylephrine-induced reduction of tissue 45Ca content (i.e. efflux of Ca2+), in tissues preloaded with 45Ca. This implies that the initial endothelial-mediated relaxant effect of carbachol in precontracted tissues cannot be explained either by reduced influx or by an enhanced efflux of Ca2+ from the smooth muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased bone formation and decreased bone resorption in fetal mouse calvaria as a result of intermittent compressive force in vitro

We have shown earlier that hypertrophic chondrocytes of growth plate cartilage in vitro react to an intermittent compressive force (ICF) of physiological magnitude by an increased calcification of the matrix. In this communication, we report the influence of ICF on bone metabolism, i.e., osteoblastic and osteoclastic activity, using fetal mouse calvaria in vitro. Seventeen-day-old calvaria were cultured for 5 days under control conditions (atmospheric pressure), or under the influence of ICF. ICF was generated by intermittently compressing the gas phase above the culture medium (130 mbar, 0.3 Hz). Osteoblastic activity was monitored by measuring alkaline phosphatase (AP) activity and 45Ca incorporation into the bone mineral. Osteoclastic resorption of the mineral phase was monitored by measuring the release of 45Ca from prelabeled bone rudiments. In addition, the total mineral content (Ca and Pi) of the calvaria was determined. Exposure to ICF resulted in a significant increase in bone formation, indicated by an enhanced alkaline phosphatase activity and increased incorporation of 45Ca, as well as a decreased bone resorption. The combined effects led to a net increase in mineral content per calvarium of some 16%. We conclude that both osteoblasts and osteoclasts are affected by intermittent compressive force. Osteoblasts are stimulated, and osteoclasts are inhibited in their activity and/or growth. The effect of ICF on osteoblasts is comparable with the effect on fetal growth plate chondrocytes; both cell types respond to ICF by an increase in calcium-phosphate mineral deposition in the matrix. The lower bone resorption may be a direct effect of ICF on osteoclasts, but it is also possible that osteoblasts play an intermediate role.

Effect of calcium agonists and antagonists on cerebellar granule cells

In cerebellar cultures, comprising predominantly granule neurones, dihydropyridine (DHP) Ca2+ agonists were potent stimulators of voltage-sensitive 45Ca2+ uptake. Their effect was maximal in partially depolarized cells; at 15 mM K+e half maximal stimulation occurred at about 5 X 10(-8) M BAY K 8644 and 10(-7) M (+)-(S)-202791. Organic Ca2+ antagonists were effective inhibitors of voltage-sensitive calcium entry into granule cells: the order of potency in blocking uptake induced by sub-maximal concentration of K+ and BAY K 8644 was nifedipine greater than (-)-202791 greater than D600. BAY K 8644 also stimulated the release of glutamate, the transmitter of the granule cells, from depolarized cells. Granule cells are therefore a class of neurones whose responsiveness to organic Ca2+ effectors is similar to that of cardiac and smooth muscle. The discrepant findings on the effect of calcium effectors in various preparations of nervous tissues may thus reflect a differential distribution of voltage-sensitive Ca2+ channels in different neuronal cell types.

Effect of 1,25(OH)2 vitamin D3 and ionized Ca2+ on 45Ca uptake by primary cultures of aortic myocytes of spontaneously hypertensive and Wistar Kyoto normotensive rats

The effect of several regulators of whole animal Ca2+ homeostasis on 45Ca uptake by primary cultures of aortic myocytes isolated from spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats was examined. Exposure of confluent cells to 1.0, 1.25 or 1.50 mM ionized Ca2+ in serum-free medium for seven days resulted in increased 45Ca uptake at the higher concentrations of Ca2+ in cells of the SHR but not the WKY. 1,25 (OH)2 vitamin D3 (1 ng/ml) for 7 days caused enhanced influx in cells from both the SHR and WKY while parathyroid hormone (1-34) (1 ng/ml) was without effect. The data indicate that humoral factors that serve to regulate whole animal Ca2+ homeostasis may also play a role in the regulation of Ca2+ metabolism of the vascular smooth muscle cell.

Effect of ruthenium red upon Ca2+ and Mn2+ uptake in Saccharomyces cerevisiae. Comparison with the effect of La3+

The initial rate of both Ca2+ and Mn2+ uptake is inhibited by ruthenium red to about the same extent as by equivalent concentrations of La3+. The inhibition of Ca2+ uptake, however, is relieved during further incubation with ruthenium red. On preincubating the cells with ruthenium red even a stimulation of divalent cation uptake can be found. Relieve of the inhibition of divalent cation uptake is accompanied by K+ efflux. Both ruthenium red and La3+ displace Ca2+ very effectively from binding sites at the cell surface. The inhibition of initial Ca2+ uptake is accompanied by a reduction in the binding of Ca2+.

The relative contributions of extracellular and intracellular calcium to secretion from tumor mast cells. Multiple effects of the proton ionophore carbonyl cyanide m-chlorophenylhydrazone

The proton ionophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) inhibited antigen-stimulated secretion and calcium influx in rat basophilic leukemia cells. In a glucose-free solution the inhibitory effects of CCCP were due to a decrease in the intracellular ATP concentration; however, when glucose was present there was no decrease in ATP. Instead, we found that in a glucose-containing saline solution, CCCP inhibited antigen-stimulated calcium uptake because it depolarized the plasma membrane, which in rat basophilic leukemia cells inhibits antigen-stimulated calcium uptake. In the presence of glucose, relatively low concentrations of CCCP inhibited calcium uptake while higher concentrations were required to inhibit secretion. In contrast, the initial antigen-stimulated rise in cytoplasmic calcium, measured with the fluorescent calcium indicator quin2, was not inhibited by CCCP. This suggests that the release of calcium from intracellular stores might, in some cases, be sufficient to support antigen-stimulated secretion. In the presence of CCCP the pH gradient becomes important for regulating the membrane potential across the plasma membrane. When cells were depolarized with CCCP and the external pH was increased, the membrane potential returned to resting levels and antigen-stimulated calcium uptake was restored. Inhibition of antigen-stimulated secretion by higher concentrations of CCCP could also be reversed by increasing the external pH.

Disposition of preformed mineral in matrix vesicles. Internal localization and association with alkaline phosphatase

Studies were made on the disposition of mineral ions in matrix vesicles (MV) and their relationship to alkaline phosphatase by treatment of MV-enriched microsomes (MVEM) with graded levels of Ca2+-chelating agents to complex accessible ions, fractionation of MVEM on hypertonic sucrose gradients at two different pH values (7.5 and 8.0) to evaluate for the presence of calcium phosphate mineral, and passage of MVEM through cation-exchange columns to determine the accessibility of the Ca2+. The effect of removal of Ca2+ and Pi on subsequent ability of MVEM to induce mineral formation from synthetic cartilage lymph was also determined. Passage through cation-exchange columns revealed that MV Ca2+ was not freely exchangeable, but coeluted in the void volume with alkaline phosphatase. However, upon incubation in synthetic cartilage lymph, progressively more Ca2+ was retained by the column. These findings indicate that, initially, the majority of Ca2+ in MVEM is internal and not readily exchangeable, but as Ca2+ accumulates, progressively more becomes external. The mineral in MV is labile and readily susceptible to loss; treatment with graded levels of EGTA removed major portions of the original Ca2+ and Pi. 45Ca uptake by these mineral-depleted MV was markedly reduced, even in the presence of alkaline phosphatase substrates. Sucrose gradient fractionation of MVEM caused extensive loss of Pi, but not Ca2+, from the low-density alkaline phosphatase-rich fractions. This reveals that Ca2+ and Pi are not initially coupled together: Pi is largely soluble, whereas Ca2+ must be tightly bound. In the high-density vesicles, large amounts of both Ca2+ and Pi are present. The slightly enhanced recovery at higher pH suggests the presence of a solid mineral phase. During mineralization by MV, Ca2+ became externalized, and concomitantly alkaline phosphatase activity declined. This suggests that a direct association exists between the enzyme and the developing mineral.

Effects of potassium and norepinephrine on calcium influx in guinea-pig vas deferens

The effects of potassium (K+) and adrenoceptor agonists on 45Ca influx and contraction of isolated vas deferens from reserpine-treated guinea-pigs has been investigated. K+ (18-84 mM) increased 45Ca influx with the maximum influx occurring at 50 mM K+. The rate of influx upon exposure to K+ was highest in the first 2 min and decreased thereafter. In contrast to K+, norepinephrine, methoxamine and xylazine did not increase the rate of 45Ca influx. Norepinephrine and methoxamine, but not xylazine, inhibited 45Ca influx induced by high K+. The inhibitory effect of norepinephrine was also present in denervated tissues. Prazosin, but not yohimbine or propranolol, blocked the inhibitory effect of norepinephrine. Potassium-induced contractions were significantly potentiated in the presence of norepinephrine, especially at low calcium concentrations. We conclude that K+ contracts the guinea-pig vas deferens by increasing the influx of calcium whereas stimulation of alpha 1-adrenoceptors prevents 45Ca influx elicited by high potassium.

Abnormal 45Ca fluxes in dispersed submandibular acini of rats treated with reserpine

The uptake and efflux of the isotopic tracer 45Ca were compared in dispersed submandibular acini of both control rats and rats treated with seven daily doses of reserpine (0.5 mg/kg, i.p.). Tracer uptake occurred in a time-dependent manner in both types of acini and reached 8.4 +/- 0.2 and 8.0 +/- 0.2 pmol/mg protein, respectively, in acini from control and treated animals after 60 min of incubation. Uptake of tracer was 2.35 nmol/mg DNA in control cells and 4 nmol/mg DNA in cells from treated rats at 60 min. 45Ca uptake (per mg protein) was enhanced in control acini 48% by 20 mumol/L epinephrine; 38% by 50 mumol/L carbachol; and 23% by 10 mumol/L isoproterenol. A similar order of potency was observed when uptake was expressed per mg DNA. In acini from reserpine-treated rats, 45Ca uptake (per mg protein) was increased 53% by epinephrine, 39% by isoproterenol, and only 8% by carbachol. The same enhanced effect of isoproterenol and lack of effect of carbachol were observed when uptake was calculated per mg DNA. In the absence of secretagogue, efflux of 45Ca from tracer-pre-loaded acini was larger in acini from reserpine-treated rats (53%) than in control acini (36%). Whether expressed in terms of mg protein or mg DNA, this efflux was increased in control acini 35% by epinephrine, from 25 to 28% by isoproterenol, and 17% by carbachol. In acini of reserpine-treated rats, epinephrine increased 45Ca efflux 20%, isoproterenol from 25 to 28%, and carbachol from 14 to 15%.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein kinase C-mediated negative-feedback inhibition of unstimulated and bombesin-stimulated polyphosphoinositide hydrolysis in Swiss-mouse 3T3 cells

Bombesin-related peptides stimulate a rapid increase in polyphosphoinositide hydrolysis in Swiss-mouse 3T3 cells. These peptides generate an increase in the efflux of 45Ca2+ from pre-labelled cells, a response consistent with an inositol trisphosphate-mediated mobilization of intracellular Ca2+. The bombesin-stimulated release of cellular 45Ca2+ is inhibited by tumour-promoting phorbol esters (e.g. 12-O-tetradecanoylphorbol 13-acetate, TPA). Although there are several possible sites of action at which this effect might occur, our results indicate that TPA induces an uncoupling of bombesin-stimulated hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) without decreasing cellular binding of bombesin. In cultured cells, protein kinase C can be down-modulated by a prolonged incubation of the cells with phorbol esters. Such pretreatment greatly decreased the inhibitory effect of TPA on bombesin-stimulated PIP2 hydrolysis, suggesting that this action of the phorbol ester is mediated via protein kinase C. Since diacylglycerol is an endogenous activator of protein kinase C and a direct product of PIP2 hydrolysis, these results suggest that protein kinase C inhibition of polyphosphoinositide hydrolysis may function as a negative-feedback pathway. Cells in which protein kinase C has been down-modulated show elevated basal and bombesin-stimulated production of inositol phosphates, providing evidence that such a feedback loop limits polyphosphoinositide turnover in both unstimulated and mitogen-stimulated cells.

Effect of 5-(3-[4-(4-fluorophenyl)-1-piperazinyl]-propoxy)indan (BP-528) on benzodiazepine receptor bindings and gamma-aminobutyric acid release

The action of a new type of anti-anxiety compound, 5-(3-[4-(4-fluorophenyl)-1-piperazinyl]-propoxy)indan (BP-528), was tested on benzodiazepine receptor bindings and on [3H]-GABA release. BP-528 did not alter [3H]-diazepam binding to rat cerebral cortical and hippocampal membranes either in the presence or absence of GABA; and the binding of [3H]-propyl-beta-carboline-3-carboxylate at low concentration (0.04 nM), which labels only the type I benzodiazepine receptor, was not changed by BP-528. BP-528 did not interact with the GABA-benzodiazepine receptor complex, which is related to the anti-anxiety activity of benzodiazepines. This compound affected neither GABA binding nor GABA uptake. Ten micromolar BP-528 depressed high K+-induced [3H]-GABA release from preloaded rat hippocampal slices. However, the same concentration of BP-528 also inhibited high K+-induced calcium uptake by rat cerebral cortical synaptosomes.

[Effect of parathyroid hormone on the transport of 45Ca2+ and 3H-GABA in nerve endings isolated from the rat cerebral cortex]

Parathyroid hormone (PTH) (0.1-10 ng/ml) evokes a dose-dependent increase in 45Ca2+ accumulation in synaptosomes isolated from the rat brain cortex. In the presence of PTH the fast (I sec) potential-dependent 45Ca2+ uptake was less than in the control. PTH had no effect on 3H-GABA uptake by synaptosomes (P2 fraction). Synaptosomes preincubated in the presence of PTH in Ca2+-free medium and transferred into Ca2+-containing normal medium released more 3H-GABA than control synaptosomes. In this case depolarization-evoked 3H-GABA release was diminished.

The cholecystokinin-induced Ca2+ shuttle from the inositol trisphosphate-sensitive and ATP-dependent pool, and initial pepsinogen release connected with cytoskeleton of the chief cell

In guinea pig chief cells, inositol 1,4,5-trisphosphate (IP3) caused release of Ca2+, which was accumulated by ATP, from an endoplasmic reticulum-enriched fraction in both the permeable system and the cell-free system. This was mimicked with the Ca2+ ionophores A23187 and ionomycin on a large scale since an IP3-sensitive Ca2+ pool might be a subset of the Ca2+ ionophore-sensitive Ca2+ pool. The permeable chief cells, but not the cell-free system, retained the ability to react to synthetic cholecystokinin octapeptide (CCK-OP) with Ca2+ release from an IP3-sensitive pool due to of the non-additive but constant effect in exerting Ca2+ release from the store(s) induced by the combination with IP3 and CCK-OP. The increase in the cytosolic free Ca2+ concentration of intact chief cells responding to CCK-OP or the Ca2+ ionophore, ionomycin, comprised two components, namely, that by the Ca2+ entry from the extracellular space, and that by the Ca2+ release from the intracellular space(s) (as measured by fura-2). When CCK-OP or ionomycin was added, there was a biphasic response of pepsinogen secretion. An initial but transient response reaching a peak in 5 min was followed by a sustained response reaching a peak in 30 min. The initial pepsinogen release was independent of medium Ca2+, whereas the sustained one was dependent on medium Ca2+. The results suggest that the intracellular Ca2+ release from the store(s), presumably endoplasmic reticulum, may trigger the initial pepsinogen release, whereas the sustained pepsinogen secretion may be caused by acting in concert with the initial response and external Ca2+ entry. On the other hand, the disruption of the microtubular-microfilamentous system by colchicine or cytochalasin D failed to cause the Ca2+ release evoked by either IP3, CCK-OP or Ca2+ ionophores and to cause the CCK-OP- or ionomycin-induced initial pepsinogen release. These findings suggest that the IP3-sensitive pool is the same Ca2+ store which is completely or partially sensitive to CCK-OP and Ca2+ ionophores, respectively, and that the assembly of the cytoskeletal system is involved in initial intracellular Ca2+ metabolism and the following initial pepsinogen release. The assembly of the cytoskeletal system may be an early event in mediating the CCK-OP-induced initial pepsinogen release, perhaps by causing the Ca2+ release from an IP3-sensitive pool of the chief cell. The translocation or attachment of the IP3-sensitive pool brought about by cytoskeletal system might be necessary to cause Ca2+ release after the cell stimulation with CCK-OP.

Do presynaptic opiate receptors and alpha-adrenoceptors alter acetylcholine release from a sympathetic ganglion by a similar mechanism?

The present experiments tested the possible involvement of a calcium-sensitive mechanism in the alpha-adrenoceptor- and opiate receptor-mediated inhibition of acetylcholine release from the cat superior cervical ganglion. First, the calcium-dependence of evoked acetylcholine release was measured in the presence and absence of the alpha-adrenoceptor agonist noradrenaline or of the opiate receptor agonist [Met5]enkephalin-Arg6-Phe7. When ganglia were perfused with Krebs medium containing [Ca2+] = 2.4, 1.2, 0.6, 0.2 mM, evoked release of acetylcholine was depressed by both agonists and the inhibition increased with reduced levels of extracellular Ca2+; this was especially evident when calcium in the medium was reduced to 0.2 mM. Second, the effects of both noradrenaline and [Met5]enkephalin-Arg6-Phe7 on calcium influx into presynaptic nerve endings was determined by measuring the accumulation of 45Ca into ganglia in the presence and absence of either drug. Both agonists reduced the stimulation-induced increase in 45Ca accumulation. The effect of noradrenaline to reduce calcium influx was blocked by yohimbine or by phentolamine; the effect of [Met5]enkephalin-Arg6-Phe7 to decrease 45Ca accumulation by ganglia was blocked by naloxone. It is concluded that activation of presynaptic opiate receptors and alpha-adrenoceptors in the cat superior cervical ganglion can alter acetylcholine release by a similar mechanism, i.e. to reduce Ca2+ influx during preganglionic nerve stimulation.

Effect of cadmium on vitamin D-non-stimulated intestinal calcium absorption in rats

The present report demonstrates the effect of Cd on intestinal Ca transport and Ca-binding protein in rats adapted to vitamin D repletion and high Ca. There were significant decreases in in vitro intestinal Ca transport in animals exposed to Cd for 2 or 3 months as compared with controls. Ca transport from everted gut sacs of normal rats showed a dose-dependent decrease. 45Ca-binding activity to intestinal mucosa from Cd-exposed rats showed a lower level of decrease than that on control rat mucosa. The typical peak of Cd-binding protein obtained from Sephadex G-100 gel filtration of 109Cd added to mucosal supernatant agreed with results of gel filtration obtained after 45Ca had been added to the same supernatant. Although there were 2 proteins binding Cd or Ca in the intestinal mucosa, with the same molecular weight of 10,000, these proteins were shown to be different, since Cd did not bind with the Ca protein. It was concluded that inhibition of vitamin-D-non-stimulated Ca transport was not caused by Cd bound to Ca-binding protein, but by some other factor.

The relationship between alpha 1-adrenergic receptor occupancy and response in BC3H-1 muscle cells

The relationship between alpha 1-adrenergic receptor occupancy by agonists or antagonists and the regulation of intracellular Ca2+ was examined. Receptor occupancy was measured using the antagonist [3H]prazosin and correlated with agonist-elicited 45Ca2+ fluxes. The agonists epinephrine (E), norepinephrine (NE), and phenylephrine (PE) coordinately activated Ca2+ efflux, reflecting a substantial mobilization of intracellular Ca2+, as well as a smaller 45Ca2+ influx. The agonist concentration dependences for influx and efflux were similar, with the order of potency expected for alpha 1 receptors (E greater than or equal to NE greater than PE). To determine the relationship between receptor occupancy and response, the slowly dissociating antagonist prazosin was used to inactivate specified fractions of the receptor population. A linear relationship was observed between the remaining activatable receptors and residual 45Ca2+ efflux elicited by E or NE, except at saturating agonist concentrations where some curvature was observed. Moreover, the concentration dependence for agonist-elicited 45Ca2+ efflux was shifted toward slightly higher concentrations of E or NE following prazosin inactivation. These results suggest the presence of a modest receptor reserve which is revealed by E or NE, but not by PE. Agonist occupation was measured over the same interval as receptor activation by competition with the initial rate of [3H]prazosin association. All three agonists exhibited the major fraction of receptor occupation over the same concentration ranges required for the functional response. Exposure of receptors to specified agonist concentrations for 30 min had little effect on the number of receptors or their ligand affinities, whereas a 2.5-hr exposure to agonist decreased apparent agonist affinity as well as the number of receptors recognized by [3H]prazosin.

Effects of nandrolone decanoate on forearm mineral density and calcium metabolism in osteoporotic postmenopausal women

Although anabolic steroids have been used for many years to treat osteoporosis there is little available evidence about their efficacy or mode of action. These agents have recently been shown to produce an increase in total body calcium and bone density and it has been suggested that they stimulate bone formation. In this study 27 osteoporotic postmenopausal women were given 50 mg of nandrolone decanoate intramuscularly, every 2 or 3 weeks for 3 months, and the changes in forearm mineral density, fasting plasma, and urinary calcium, urinary hydroxyproline, and radiocalcium absorption were measured. Associated with a rise in forearm mineral density was a significant fall in fasting urinary calcium, but no significant change in fasting urinary hydroxyproline. The plasma calcium and phosphate fell significantly and there was a significant rise in the renal tubular reabsorption of calcium and a fall in the renal tubular reabsorption of phosphate. In a subset of 22 patients there was a significant rise in radiocalcium absorption. The results are consistent with the concept that nandrolone exerts a significant positive effect on bone formation and that this results in a fall in the fasting plasma calcium level, and consequently calcium excretion.

Heterogeneity of presynaptic calcium channels revealed by species differences in the sensitivity of synaptosomal 45Ca entry to omega-conotoxin

The inhibition of K+-depolarization dependent Ca influx by omega-conotoxin GVIA was compared in the frog, chick, and rat brain synaptosomes. The toxin at concentrations greater than or equal to 0.3 microM completely inhibited Ca entry in the frog and chick preparations, but was only partly effective in blocking Ca influx in the rat brain synaptosomes. In chick synaptosomes the toxin's effect was biphasic: a small component (approximately equal to 15%) of total Ca influx was inhibited by the toxin with high affinity (I50 less than 0.002 microM); a major component (approximately equal to 80%) of Ca influx was inhibited with a moderate affinity (I50 approximately equal to 0.05 microM). In rat brain synaptosomes 40% of Ca influx was inhibited by the toxin with low affinity (I50 approximately equal to 0.3 microM), and 60% of Ca influx was unaffected by the toxin concentration of up to 10 microM. These data suggest a heterogeneity of voltage-sensitive Ca channels in vertebrate brain synaptosomes.