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C R Kleeman

Publications and source records attributed to C R Kleeman.

At least 19 recordsLinked to original sources
PubMed1992

Dissociation between parathyroid hormone-stimulated cAMP and calcium increase in UMR-106-01 cells.

We used the osteogenic sarcoma cell line, UMR-106-01, to determine whether the rise in free cytosolic Ca2+ concentration ([Ca2+]i) and cellular cAMP following PTH stimulation are able to be regulated independently. For this purpose, we compared the effect of a PTH antagonist, stimulation of protein kinase C, augmentation by prostaglandins, and the time course of desensitization of the two cellular responses. Two x 10(-7) M of the PTH antagonist 8,18Nle 34Tyr-bPTH(3-34) amide ([Nle,Tyr]bPTH(3-34)A) was required to inhibit 10(-9) M bPTH(1-34)-stimulated cAMP generation by 50%. 10(-7) M bPTH(1-34) completely overcame the inhibition induced by 10(-6) M [Nle,Tyr]bPTH(3-34)A. Only 7 x 10(-8) M and 2.7 x 10(-7) M [Nle,Tyr]bPTH(3-34)A were required to half maximally inhibit the [Ca2+]i increase evoked by 3 x 10(-8) and 10(-7) M bPTH(1-34), respectively. In addition, dissociation between [Ca2+]i and cAMP signals was observed when modulation by protein kinase C and prostaglandins was tested. Preincubation of the cells with 10 nM TPA for 5 minutes markedly inhibited the PTH-evoked [Ca2+]i increase. Short incubation with PGF2 alpha augmented the PTH-evoked [Ca2+]i increase. Similar pretreatments had no effect on the PTH-stimulated cAMP increase. Finally, preincubation with 1.5 x 10(-9) M bPTH(1-34) for 20 minutes almost completely blocked the effect of 10(-7) M bPTH(1-34) on [Ca2+]i, while preincubation with 5 x 10(-9) M bPTH(1-34) for 4 hours was required to inhibit the effect of 10(-8) M bPTH(1-34) on cAMP production by 50%. The differences in the regulation of the two PTH-stimulated cellular signaling systems, in particular, the response to antagonists and the time course of desensitization, could be at the level of the PTH receptor(s) or at a postreceptor domain.

Calcium↗
PubMed1992

Role of calcium and cAMP messenger systems in intracellular pH regulation of osteoblastic cells.

We have recently shown that two mechanisms are involved in the regulation of pHi in the osteoblastic phenotype cell line UMR-106 (Na(+)-H+ antiporter and a Na(+)-independent Cl(-)-HCO 3(-)-OH- exchanger). In the present work, we used the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein as well as isotope fluxes to investigate the influence of second messengers on the activity of these transporters. Elevation in intracellular calcium concentration [( Ca2+]in) in UMR-106 cells (measured by fura-2 fluorescence) is followed by stimulation of the Cl(-)-HCO3- exchanger, leading to cytosolic acidification. Subsequently, cell alkalinization, mediated by the Na(+)-H+ exchanger, restores pHi to its resting value. An acute reduction in [Ca2+]in abruptly stops the activity of the anion exchanger while having no influence on the activity of the Na(+)-H+ exchanger. The stimulatory effect of Ca2+in on the anion exchanger is dose dependent and is abrogated by the calmodulin inhibitors N-(6-aminohexyl)-5-chloro-naphthalenesulfonamide and calmidazolium. An increase in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) brought about by forskolin, 8-bromo-cAMP, or prostaglandin E2 leads to inhibition of activity of both the Na(+)-H+ antiporter and the anion exchanger. The suppressive effect of cAMP on Cl(-)-HCO3- exchange could be overcome by elevating [Ca2+]in. We conclude that 1) Ca2+in and cAMP can influence pHi in osteoblasts by altering the activities of pHi regulatory mechanisms and 2) the effect of Ca2+in is probably mediated by calmodulin.

Anions↗
PubMed1992

1,25(OH)2D3 blunts hormone-elevated cytosolic Ca2+ in osteoblast-like cells.

Cytosolic free calcium ([Ca2+]i) is an important regulator of bone cell physiology. We studied the interaction of vitamin D metabolites on the hormonal-activated Ca message system in the osteoblastic cell line UMR-106. The acute rise in [Ca2+]i induced by different calciotropic hormones [parathyroid hormone, prostaglandin E2 (PGE2)] was dose dependently blunted by 1,25-dihydroxyvitamin D [1,25(OH)2D3; half-maximal inhibitory concn approximately 5 x 10(-11) M] and was initially observed after 8 h of preincubation. The 1,25(OH)2D3 metabolite of vitamin D was two orders of magnitude more potent than 24,25(OH)2D3 and 25(OH)D3. To discern between an effect of 1,25(OH)2D3 on hormonal-induced Ca2+ entry through the plasma membrane channel vs. release of Ca2+ from internal stores, we suspended fura-2-loaded cells in Mn2+ rather than Ca2+ buffers. In cells preincubated with 1,25(OH)2D3, [Ca2+]i release (indicated by [Ca2+]i transient) was significantly blunted, whereas Mn2+ influx (indicating Ca2+ flux across the plasma membrane) was unaltered, suggesting a selective effect of 1,25(OH)2D3 on hormonal-activated release of Ca2+ from intracellular stores. 1,25(OH)2D3 also inhibited the PGE2-induced production of inositol 1,4,5-trisphosphate. We conclude that, in osteoblasts, chronic (hours) incubation with 1,25(OH)2D3 leads to attenuated stimulation of the [Ca2+]i transduction pathway by calciotropic hormones. This effect of 1,25(OH)2D3 may provide a cellular basis for the synergism between the effects of vitamin D and calciotropic hormones at the bone level.

Calcitriol↗
PubMed1991

Voltage-dependent phosphate transport in osteoblast-like cells.

Phosphate ion (Pi) in sufficient concentrations is crucial for bone mineralization. The osteoblast (OB) may be responsible for the transport of Pi into the bone interstitium, where mineralization occurs. We previously characterized a Na(+)-dependent Pi transporter (NaPi) in the osteoblastic UMR-106-01 cell line. In the present study, the alteration of Na(+)-dependent Pi transport by changes in membrane potential was investigated. Depolarizing the cells with increasing concentrations of ambient K+ and valinomycin resulted in a progressive decline in Na(+)-dependent Pi uptake to a maximum of 28% at a membrane potential of -18 mV compared to control Na(+)-dependent Pi uptake at a membrane potential of approximately -60 mV. Hyperpolarizing the cells with SCN- increased Na(+)-dependent Pi uptake over control by 50% at an SCN- concentration of 70 mM. Determination of membrane potential by using the fluorescent probe, DiSC3(5), showed that the addition of Pi to cells in Na(+)-containing medium resulted in a small depolarization. These data show that NaPi activity can be altered by membrane potential changes and that the initiation of Na(+)-dependent Pi uptake is associated with depolarization of the plasma membrane of UMR-106-01 cells. Taken together, the cotransport of Na+ and Pi results in the movement of a net positive charge into the cell.

Benzothiazoles↗
PubMed1991

Prostaglandins enhance parathyroid hormone-evoked increase in free cytosolic calcium concentration in osteoblast-like cells.

Prostaglandins (PGs) are autocrine or paracrine hormones that may interact with circulating hormones such as parathyroid hormone (PTH) in bone. We examined the interaction of the PGs, PGF2 alpha, PGE2, and 6-keto-PGF1 alpha with PTH to enhance the rapid, initial transient rise in free cytosolic calcium ([Ca2+]i) and cAMP levels stimulated by PTH. Pretreatment of UMR-106, MC3T3-E1, and neonatal rat calvarial osteoblast-like cells by PGs resulted in an enhancement of the early transient rise in [Ca2+]i stimulated by PTH. PGF2 alpha was approximately 100 times more potent than PGE2. PGE2 itself was more potent than 6-keto-PGF1 alpha in enhancing PTH-stimulated rise in [Ca2+]i. Near-maximal augmentation was achieved at PGF2 alpha doses of 10 nM and PGE2 of 1 microM. The degree of augmentation in [Ca2+]i by PGF2 alpha was independent of preincubation time. PGF2 alpha pretreatment did not alter the EC50 for the PTH-induced [Ca2+]i increase but only the extent of rise in [Ca2+]i at each dose of PTH. The augmented increase in [Ca2+]i was mostly due to enhanced PTH-mediated release of Ca2+ from intracellular stores. PGF2 alpha did not stimulate an increase in PTH receptor number as assessed by [125I]-PTH-related peptide binding. PG pretreatment partially reversed PTH inhibition of cell proliferation, suggesting that an increase in [Ca2+]i may play a role in tempering the anti-proliferative effect of PTH mediated by cAMP. These studies suggest a new mode by which PGs can affect cellular activity.

6-Ketoprostaglandin F1 alpha↗
PubMed1991

Acute phosphate depletion dissociates hormonal stimulated second messengers in osteoblast-like cells.

The acute effect (24 h) of either phosphate depletion or phosphate surfeit on hormonal stimulated signal transduction systems was studied in the osteoblastic cell line UMR-106. Elevation of intracellular Ca2+ ([Ca2+]in), induced by different calciotropic hormones (PTH, prostaglandin E2, endothelin) was blunted by acute phosphate depletion, whereas at high inorganic phosphate (Pi) concentrations the rise in [Ca2+]in was augmented. Basal [Ca2+]in was not altered by either Pi depletion or Pi excess. The effect of acute phosphate depletion on hormonal mediated [Ca2+]in rise was not observed in the absence of extracellular Ca2+ suggesting that under these conditions, the release of Ca2+ from intracellular stores, is not affected. Also, nonhormonal calcium entry pathways such as depolarization-activated calcium channels or protein kinase C-activated Ca2+ channels were not affected by acute phosphate depletion. cAMP accumulation in the cells, either through receptor or nonreceptor-mediated mechanisms, increased under low Pi conditions and decreased as Pi concentration in the culture media was progressively increased from 0 to 2 mM during 24 h of incubation. Changes in Pi concentration had no effect on basal cAMP generation by the cells. The facilitative effect of acute Pi depletion on agonist-induced cAMP accumulation could be demonstrated in both the presence and absence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.2 mM). PTH receptor binding assessed with [Nle8 Nle18 Tyr34] bovine PTH (1-34) NH2 was not altered by phosphate depletion. We conclude that exposure of osteoblasts to different Pi environments modulates the second messenger responses to hormones in a reciprocal fashion so that acute phosphate depletion down-regulates [Ca2+]in signals while augmenting cAMP generation and vice versa. Inasmuch as bone resorption processes can be modulated by Ca2+ and cAMP the data presented herein suggest that the altered bone resorptive response to calciotropic hormones (e.g. PTH), under surfeit or deficit of phosphate, is mediated by changes in [Ca2+]in and cAMP.

1-Methyl-3-isobutylxanthine↗
PubMed1979

Causes of hypercalcemia.

Hypercalcemia is most commonly seen in normal infants as the result of normal rapid bone growth. The most common causative diseases are malignant disease and hyperparathyroidism. A variety of pharmacologic agents, especially vitamin D and its metabolites and thiazide diuretics, can elevate serum calcium levels. Hypersensitivity to vitamin D appears to be a cause of hypercalcemia in infants and in patients with granulomatous disease, such as sarcoidosis. Ingestion of escessive amounts of calcium, especially with alkali, may also cause hypercalcemia, as may prolonged immobilization, particularly under conditions of rapid bone turnover.

Adult↗
PubMed1979

Management of hypercalcemia.

Hypercalcemia calls first for supportive measures, eg, adequate hydration, movement or mobilization of the patient to the greatest amount tolerated, and reevaluation of drugs being taken. When immediate lowering of the serum calcium level is not clinically mandatory, oral administration of furosemide, corticosteroid, or phosphorus should be considered. In acute emergencies, saline loading and parenteral furosemide therapy should be tried first, except in a patient with renal failure and congestive heart failure, in whom peritoneal dialysis or hemodialysis should be used instead. Calcitonin can be given for the first 12 to 24 hours to lower serum calcium concentration until a definitive management plan is formulated. Corticosteroid, if not contraindicated, should be started as soon as possible. In severe primary hyperparathyroidism with hypophosphatemia, phosphorus can be given intravenously until oral phosphate therapy can be established. Surgery, of course, should be performed as soon as possible. In most cases of neoplasia, mithramycin given according to a recommended schedule is safe and frequently effective. In desperate cases, additional use of prostaglandin synthesis inhibitors probably now is justified by empirical observations. All of these therapeutic measures are used only to stabilize electrolyte balance so that the primary cause of the hypercalcemia can be treated.

Adrenal Cortex Hormones↗
PubMed1979

Normophosphatemic phosphate depletion in growing rat.

To study the influence of phosphate depletion (PD) on the serum, urinary, bone, and soft tissue phosphorus, we studied growing rats given a high-phosphorus (HP), normal-phosphorus (NP), or low-phosphorus (LP) diet. We obtained the following results. a) With an LP diet, animals did not grow but developed the characteristic biochemical changes of PD. b) The NP rats had an unexplained accelerated rate of growth, and developed all the biochemical changes of PD, although they were normophosphatemic. c) Bone P and Ca were significantly lower in the LP and NP rats compared to the HP rats, suggesting that minerals were mobilized from bone to support soft tissue P needs. d) Soft tissue P was not different in HP, NP, and LP rats, confirming previous observations that soft tissue P is maintained even in PD. We conclude that 1) the physiologic adaptation to PD may occur in growing rats on an apparently normal phosphorus diet when the metabolic demand is unusually high, e.g. accelerated growth; 2) the evolution of the biochemical parameters of PD in the face of normophosphatemia suggest a sensor mechanism sensitive to change in dietary P concentration.

Animals↗
PubMed1979

Effect of phosphorus depletion on intestinal calcium and phosphorus absorption.

Intestinal calcium (Ca) hyperabsorption is a well-documented feature of experimental phosphorus depletion (PD). To further evaluate the effect of PD on Ca absorption we studied metabolic balance and in vitro everted duodenal sac uptake of Ca and phosphorus (P) in weanling male rats. Animals were assigned to three dietary groups: normal, 0.3% P ad libitum (NP); low, 0.03% P ad libitum (LP); and normal, 0.3% P but pair-fed with assigned LP mates (NP-PF). Results indicate that although PD led to an early but unsustained increase in 45Ca uptake by the everted duodenal sac in vitro, net intestinal Ca retention is consistently decreased in rats on the LP diet compared with rats eating either the NP or NP-PF diet. The reduction in net intestinal Ca absorption is reflected by an increase in fecal Ca, both in absolute quantities and in proportion to dietary Ca intake. The initial negative P balance after the initiation of the LP diet was promptly, albeit precariously, corrected. This was associated with a sustained increase in duodenal 32P uptake in vitro and virtual cessation of growth. Because the biosynthesis of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and its accumulation in intestinal mucosa have been reported to increase with PD, our study represents an example in which the physiological interrelationship between the activity of 1,25(OH)2D3 and intestinal Ca absorption may be dissociated.

Animals↗
PubMed1979

Influence of dietary magnesium in experimental phosphate depletion: bone and soft tissue mineral changes.

We studied weanling rats fed 0.06% (group 1) and 0.10% (group II) magnesium (Mg) during phosphate depletion (PD) in order to evaluate the role of Mg in the bone, soft tissue, and serum changes of PD. The following results were obtained: 1) serum Mg remained stable in the face of a negative Mg balance; 2) the hypercalcemic and hypercalciuric response to PD was the same in both groups; 3) bone Mg content was decreased with PD in both groups and was associated with a significant decrease in bone calcium and phosphorus. We conclude that: 1) the hypomagnesemia of PD is dependent mainly on the dietary intake of Mg; 2) the hypercalcemia and hypercalciuria of PD are not caused by primary changes in Mg homeostasis; 3) low-dietary Mg during PD may cause a defect in soft tissue utilization of P in the growing rat.

Animals↗
PubMed1979

Interaction of somatostatin with PTH and AVP: renal effects.

Six conscious intact dogs were studied to evaluate the interactions of somatostatin (SRIF) with exogenous antidiuretic hormone arginine vasopressin (AVP). SRIF administration caused a significant increase in free water clearance compared to a vehicle-treated group: -0.91 (+/- 0.41 SD) ml/min to 0.21 (+/- 0.32 SD) ml/min in the experimental group (P less than 0.01) versus 0.21 (+/- 0.81 SD) ml/min to -0.21 (+/- 0.68 SD) ml/min in the control (P greater than 0.5). Six conscious, thyroparathyroidectomized dogs were studied to test the interaction of SRIF and parathyroid extract (PTE). There were no significant changes in the phosphaturic and hypocalciuric effects of PTE with SRIF administration. We conclude that acute systemic SRIF administration interferes with the antidiuretic action of AVP, probably at the renal-tubular level, but does not antagonize the renal actions of PTE.

Animals↗
PubMed1979

Transient hypoaldosteronism after renal allotransplantation.

Studies were performed to investigate the nature of the hyperkalemia and hypokaliuria observed in two patients after renal allotransplantation in both of whom the graft was functioning and urinary output was adequate. In the first patient, examinations in the upright position revealed low values for plasma renin activity and plasma aldosterone. The second patient showed similar findings, and, in addition, an angiotensin II (Hypertensin) infusion was ineffective in stimulating aldosterone secretion during the hyperkalemic state. In both patients, short-term administration of 9 alpha-fluorohydrocortisone caused kaliuresis with a definite decrease in serum potassium. There was a spontaneous correction of the biochemical and hormonal abnormalities six weeks after transplantation and the response to an angiotensin II infusion normalized. We suggest that the hyperkalemia in both of these patients was due primarily to the transient failure of the renin-angiotensin system of the transplanted kidney.

Adult↗
PubMed1979

Mannitol.

Mannitol may be useful clinically both as a diuretic and as an obligate extracellular solute. As a diuretic it can be used to treat patients with intractable edema states, to increase urine flow and flush out debris from the renal tubules in patients with acute tubular necrosis, and to increase toxin excretion in patients with barbiturate, salicylate or bromide intoxication. As an obligate extracellular solute it may be useful to ameliorate symptoms of the dialysis disequilibrium syndrome, to decrease cerebral edema following trauma or cerebrovascular accident, and to prevent cell swelling related to renal ischemia following cross-clamping of the aorta. Largely unexplored uses for mannitol include its use as an osmotic agent in place of dextrose in peritoneal dialysis solutions, its use to maintain urine output in patients newly begun on hemodialysis, and its use to limit infarct size following acute myocardial infarction.

Acute Kidney Injury↗