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Aim: Cardiac basal metabolism upon extracellular calcium removal and its relationship with intracellular sodium and calcium homeostasis was evaluated. Methods: A mechano-calorimetric technique was used that allowed the simultaneous and continuous measurement of both heat rate and resting pressure in arterially perfused quiescent adult rat hearts. Using pharmacological tools, the possible underlying mechanisms related to sodium and calcium movements were investigated. Results: Resting heat rate (expressed in mW g-1 dry wt) increased upon calcium withdrawal (+4.4 ± 0.2). This response was: (1) unaffected by the presence of tetrodotoxin (+4.3 ± 0.6), (2) fully blocked by both, the decrease in extracellular sodium concentration and the increase in extracellular magnesium concentration, (3) partially blocked by the presence of either nifedipine (+2.8 ± 0.4), KB-R7943 (KBR; +2.5 ± 0.2), clonazepam (CLO; +3.1 ± 0.3) or EGTA (+1.9 ± 0.3). The steady heat rate under Ca2+-free conditions was partially reduced by the addition of Ru360 (-1.1 ± 0.2) but not CLO in the presence of EGTA, KBR or Ru360. Conclusion: Energy expenditure for resting state maintenance upon calcium withdrawal depends on the intracellular rise in both sodium and calcium. Our data are consistent with a mitochondrial Ca2+ cycling, not detectable under normal calcium diastolic levels. The experimental condition here analysed, partially simulates findings reported under certain pathological situations including heart failure in which mildly increased levels of both diastolic sodium and calcium have also been found. Therefore, under such pathological conditions, hearts should distract chemical energy to fuel processes associated with sodium and calcium handling, making more expensive the maintenance of their functions. Fil: Bonazzola, Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Cardiológicas; Argentina Fil: Takara, Delia. Universidad de Buenos Aires. Facultad de Odontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Male Lewis rats (n = 27) were fed a nonpurified diet containing 0.9% calcium, 0.7% phosphorus, and 0.005% zinc until 8 wk of age. At this time rats were assigned randomly to one of two groups. Both groups were fed a low calcium, low zinc, purified diet (0.2% calcium, 0.4% phosphorus, less than 0.00007% zinc), but one group was fed 1.78 mg Zn/(animal.d). The zinc-replete animals were individually matched by weight to the zinc-depleted animals and pari-fed. Balances and plasma concentrations of zinc, calcium, and phosphorus and parathyroid hormone, 25 hydroxycholecalciferol [25(OH)D] and 1,25-dihydroxycholecalciferol [1,25(OH)2D] were determined at the start of calcium depletion and 2 wk later. Calcium and 25(OH)D levels were lower in both groups after calcium depletion. Dietary zinc had no significant effect on calcium or 25(OH)D levels. Phosphorus concentrations were lower after calcium depletion, but phosphorus concentration was higher in the zinc-depleted compared with the zinc-replete group at the end of the experiment. 1,25(OH)2D increased in both groups, but was higher in the zinc-replete than the zinc-depleted group at the end of the experiment. Calcium and phosphorus balances were greater in the zinc-depleted group at the end of the experiment. We conclude zinc depletion diminishes the response of 1,25(OH)2D to calcium depletion in rats. The mechanism is unknown, but may involve nonhormonally mediated changes in gastrointestinal absorption of calcium and phosphorus or an affect of zinc on extraintestinal processes.

The effect of adenosine on the calcium paradox in the isolated frog heart was studied. Addition of adenosine during calcium depletion protected the frog heart against a calcium paradox. This protective effect was indicated by reduced protein and creatine kinase release, maintenance of electrical activity, and recovery of mechanical activity during reperfusion. Tissue calcium determination results showed that adenosine protected frog myocardial cells by reducing the massive calcium influx during reperfusion possibly through an action on calcium channels. Adenosine exerted its action in a dose-dependent manner; a concentration of 10 μM adenosine provided maximum protection of myocardial cells against the calcium paradox damage. Higher concentrations of adenosine produced side effects on both electrical and mechanical activity. These results are discussed in terms of the possible mechanism involved in the protective effect of adenosine.Key words: calcium paradox, adenosine, frog heart.

Previous studies in a weanling rat model indicated that dietary calcium depletion not only stimulated osteoclastic resorption but also inhibited bone formation. The present study sought to test whether the depletion-associated inhibition of bone formation is related to a reduction in serum insulin-like growth factor-I (IGF-I) and/or an increase in its binding proteins (IGFBPs). Twenty male weanling rats were divided into two weight-matched groups. The study group was subjected to a semisynthetic diet deficient in calcium (0.02% calcium) for 28 days, while the control group was pair-weighed on the same diet but containing 0.62% calcium. After the depletion phase, all rats were fed the same calcium-containing diet for an additional 14 days. Serum samples were obtained from each animal on a weekly basis and assayed for IGF-I and IGFBPs. During depletion, there was no statistically significant difference in serum IGF-I level between the study group and the control group. In contrast, the study group showed a statistically significant increase in several serum IGFBPs with apparent molecular size of 30-38 kD (IGFBP-3), 26-28 kD (IGFBP-1, -2, -5, and/or -6), and 24-25 kD (IGFBP-4), respectively, compared to the control group. There was no difference in nutritional intakes between the two groups of rats during depletion. During repletion, there was also no significant difference in serum IGF-I level between the control and study group. However, during the first 7 days of repletion, serum IGFBP-3 and the 26-28 kD IGFBP of the study group was significantly less than those of the control group, which then returned to the control level after 2 weeks of repletion. In summary: (1) calcium depletion in weanling rats increased several serum IGFBPs without an effect on IGF-I; and (2) calcium repletion induced an acute reduction in serum IGFBP-3. In conclusion, these findings represent the first evidence that the depletion-related inhibition of bone formation in the rat may be associated with an increase in several serum IGFBPs, which may act to inhibit the osteogenic actions of IGFs.

Female Wistar rats were separated into 9 groups, and 9 different synthetic diets (each diet contains different level of protein and calcium) were given to each group. After 5 weeks of these dietary regimens, all rats were sacrificed and calcium, magnesium, and phospho-rus levels in plasma and various tissues were determined. In calcium-deficient groups, calcium, magnesium, and phosphorus level in bone decreased, plasma calcium level decreased and there was a tendency that magnesium levels in brain and liver and phosphorus level in brain in-creased. When comparison was made among the calcium-deficient groups, calcium, magnesium, and phosphorus levels in bone were higher in low protein/calcium-deficient group than higher protein/calcium-deficient groups. It is probable that protein deficiency inhibits calcium depletion and consequently the influence of calcium deficiency is less significant in the condition of deficiency in both protein and calcium.

Among patients exposed to hydrofluoric acid the potentially lethal effect of calcium depletion induced by binding with fluoride ion has not been well reported. Three patients exposed to hydrofluoric acid had acute fluoride poisoning with serum calcium levels equal to or below 4.1 mgm/dl. Treatment included administration of large amounts of calcium, both intravenously and by subsechar injection, to replenish the biologically active calcium and to bind fluoride. This report describes successful treatment of two survivors, apparently the first two, of severe hypocalcemia caused by hydrofluoric acid.

The role of Ca2+ in the in situ secretory response of rat colon and pig ileum was studied by chelation depletion of Ca2+ and by treatment with chlorpromazine. The effect of depleting lumenal Ca2+ by chelation and the effect of intraperitoneal administration of chlorpromazine were determined relative to colonic permeability and net fluid flux measured across the rat colon or pig ileum. Replacement of Ca2+ in the perfusate by 1.0 mM ethyleneglycol-(bis-beta-ethylaminoether) (EGTA) did not produce significant changes in the net absorptive fluid flux measured in the control state or in the net secretory fluid flux caused by secretory detergent agents. The concentration of EGTA used in the perfusate did not alter mucosal permeability. Nonsecretory bile acids or A23187 had no effect on net colonic fluid flux or on colonic permeability to mannitol in the rat. The known correlation between net fluid flux and increased colonic permeability to polar molecules has been confirmed for the secretory detergent compounds. Chlorpromazine pretreatment caused a partial reversal of net secretory fluid fluxes induced by deoxycholate and high concentrations (6.0 mM) of ricinolate and dioctyl sulfosuccinate without significantly altering mucosal permeability to mannitol. We conclude that depletion of lumenal Ca2+ is not an effective method for determining the possible Ca2+ dependence of these intestinal secretory events. The antisecretory actions of chlorpromazine may provide some indirect evidence for Ca2+ involvement in the secretory effects of the detergent class of laxative compounds. Permeability may be essential for secretion caused by these agents, but the driving force would appear to be provided by the active transfer of electrolytes from the blood to the lumen of the colon.

Epidemiologically, there is a remarkably consistent picture of the relationship between calcium depletion and the development of hypertension—apparently independent of weight, cigarette smoking, alcohol intake, and other risk factors. Typically, the inverse correlation between dietary calcium and blood pressure is more evident with systolic than with diastolic pressures.

THE EFFECTS OF CALCIUM DEPLETION OF CARDIAC MUSCLE UPON THE RELATION BETWEEN STIMULUS PATTERN AND ACTION POTENTIAL, ANALYSED IN TERMS OF A MATHEMATICAL MODEL

1. In growing rats oestrogen, cortisone and thyroxine in high doses suppress bone formation, and this effect is probably part of a general suppression of body growth. 2. Growth hormone and thyroxine in small doses stimulate both body growth and bone formation. 3. Testosterone has no effect on bone formation. 4. Oestrogen and cortisone suppress bone resorption. The effect of cortisone may be modified in conditions of calcium depletion. 5. Thyroxine appears on the other hand to increase bone resorption. 6. Testosterone has no effect on bone resorption.

THE retention of radiocalcium or radiostrontium in bones of humans (Spencer et al., 1961), rats (Cohn et al., 1961) and non-laying pullets (Hurwitz, 1965a), following a single intravenous dose, is reduced by the feeding of high-calcium diets. However, in the laying hen, the severe calcium depletion from bone during calcium restriction (Taylor and Moore, 1954; Hurwitz and Griminger, 1961) would suggest the possibility of reducing the body burden of bone-seeking radiosotopes by calcium restriction. It was the purpose of the present study to investigate the effects of variation in dietary calcium level and sources, and the timing of this variation, on the retention of calcium-45 and strontium-85 in various bone segments, and the deposition of these nuclides in the egg shell. METHODS AND RESULTS General procedure: The method for preparation of samples for analysis was given in detail in the preceding paper (Hurwitz and Bar, 1966). For calcium-45 determinations, calcium …

Excised mouse thyroids incubated in Ca++-free medium were stimulated to release increased amounts of stable thyroxine. This stimulation of thyroxine release by incubated thyroid tissue was not additive with TSH or (Bu)2cAMP. It was reversed by norepinephrine through an alpha adrenergic receptor, similar to TSH or (Bu)2cAMP stimulation. Depletion of Ca++ did not result, however, in an increase in the concentration of cAMP in incubated thyroid glands, suggesting that its locus of action was subsequent to TSH stimulation or cAMP production.

The change in responsiveness to a-adrenergic stimulation and to calcium ions in amylase release from parotid glands of hypothyroid rats was compared with that in euthyroid rats. Calcium depletion and addition of verapamil or W-7 in the medium caused a decrease in methoxamine-induced amylase release in both eu- and hypothyroid rats. Moreover, addition of calcium ions to Ca2+-free medium markedly increased the methoxamine-induced amylase release in proportion to its concentration in hypothyroid rats. These results suggest that calcium ions play an important role in methoxamine-induced amylase release from parotid glands of hypothyroid rats as well as those of the euthyroid ones.

This contribution defines the ultrastructural characteristics of two very different conditions which can both lead to very extensive, and in some ways rather similar, myocardial injury. The two conditions are oxygen depletion and repletion and calcium depletion and repletion. Both conditions are of clinical relevance and both have been studied extensively in the laboratory, revealing in the process a great deal of valuable information about cellular injury and its prevention.

Calcium-free incubation followed by exposure to Ca produces ultrastructural damage in the intact myocardium—a phenomenon known as the Ca paradox. Controversy exists as to whether the observed Ca overload during Ca repletion is a primary cause for, or a secondary consequence of, sarcolemmal disruption and cell injury. In these experiments cultured embryonic chick heart cells have been subjected to Ca depletion/repletion to explore the structural, transport and metabolic mechanisms by which cells may be irreversibly damaged.Monolayer muscle enriched cell cultures were prepared by serial trypsin-disaggregation of 11-day old chick embryo hearts. Cells were incubated for 10 or 120 min in Ca-free (1 mM EGTA) Hepes-buffered salt solution (pH 7.4) followed by incubation for 60 or 180 min in the same solution containing 1 mM Ca. In another series of experiments, the mitochondrial uncoupling agent carbonyl cyanide chlorophenylhydrazone (CCCP, 10 μM ) was added during depletion and repletion.