PubMed Health⌕ Search

Biomedical subjects

R L Boland

Publications and source records attributed to R L Boland.

At least 19 recordsLinked to original sources
PubMed1998

Studies suggesting the participation of protein kinase A in 1, 25(OH)2-vitamin D3-dependent protein phosphorylation in cardiac muscle.

We have previously established that the secosteroid hormone 1alpha, 25-dihydroxy-vitamin D3 [1,25(OH)2D 3] rapidly stimulates dihydropyridine-sensitive calcium channel-mediated Ca2+ influx in chick cardiac muscle by a non-genomic action which is accompanied by phosphorylation of microsomal proteins. In the present study, we investigated the participation of the cyclic AMP/protein kinase A (PKA) signalling pathway in hormone-induced changes on protein phosphorylation in chick heart tissue. A major increase in the phosphorylation of a microsomal protein of 45 kDa, and, to a lesser extent, of a protein of 70 kDa, was observed after incubation with [gamma-32P]ATP of membranes isolated from heart thin slices (HTS) pretreated for 1-5 min with 1,25(OH)2D3. This effect was dose- and time-dependent, reaching a maximum after 3 min and at the physiological concentrations of 10(-10) and 10(-11) M. 1,25(OH)2D3 steadily increased cellular cAMP levels as a function of the dose (10( -12)-10(-9) M). The specific agonist of PKA, Sp-cAMPS and the PKA catalytic subunit stimulated the phosphorylation of the same membrane proteins as the hormone. The 1alpha,25-dihydroxy-vitamin D3-dependent changes in microsomal protein phosphorylation were diminished by the specific PKA inhibitor, Rp-cAMPS. In addition, the PKA activity ratio (-cAMP/+cAMP) increased 60% above the control after treatment of HTS with 10(-11) M 1,25(OH)2D3. The data obtained clearly indicate that activation of the cAMP/PKA signalling pathway mediates the stimulation of protein phosphorylation by 1alpha, 25-dihydroxy-vitamin D3 in chick cardiac muscle.

Animals↗
PubMed1997

1 alpha,25-(OH)2-vitamin D3 stimulates the adenylyl cyclase pathway in muscle cells by a GTP-dependent mechanism which presumably involves phosphorylation of G alpha i.

To further understand the mechanism underlying 1,25(OH)2D3 activation of the cAMP pathway, the effect of the hormone on adenylyl cyclase (AC), GTPase and protein kinase A (PKA) activities as well as on the phosphorylation of G alpha i was studied in membranes from chick skeletal muscle cells. The sterol stimulated AC activity in a dose (0.1-10 nM) and time (1-5 min.) dependent fashion, provided GTP (10 microM) was present in the assay. High affinity GTPase activity was unaffected by the hormone. In the absence of GTP or in the presence of Mn2+ (20 mM), 1,25(OH)2D3 effects on AC were abolished. PKA activity was increased (+120%) in cells pretreated (1 nM, 5 min.) with the sterol. Moreover, immunoprecipitation of G alpha i from [32P]-labeled myoblast membranes showed that 5 min. exposure to 1 nM 1,25(OH)2D3 increased (1.5-2 fold) the phosphorylation of its alpha subunit. The present data suggest that in muscle cells, 1,25(OH)2D3 activates AC by a non direct, GTP-dependent action which could imply amelioration of Gi function by sterol-induced alpha i phosphorylation.

Adenylyl Cyclases↗
PubMed1997

Vitamin D receptor expression in chicken muscle tissue and cultured myoblasts.

Muscle has long been recognized as a target tissue for 1,25-dihydroxy-vitamin D3 (1,25[OH]2D3). Evidence of the presence of VDR is provided here, thus supporting the existence of a receptor-mediated mechanism of action of 1,25(OH)2D3. Vitamin D receptor (VDR) expression is evidenced by detection of VDR-mRNA, through reverse transcription and polymerase chain reaction (RT/PCR), in chicken muscle and muscle cells (myoblasts) as well as in a variety of tissues such as intestine, kidney, heart and brain. VDR presence is also demonstrated by Southern blot of PCR products with a specific VDR-cDNA probe and by immunocytochemistry carried out on myoblasts and cardiac myocytes. Localization of VDR is mainly nuclear and more faintly detected in the cytosol.

Animals↗
PubMed1996

Age-associated decrease in inositol 1,4,5-trisphosphate and diacylglycerol generation by 1,25(OH)2-vitamin D3 in rat intestine.

The hormonal form of vitamin D3, 1,25(OH)2-vitamin D3(1,25[OH]2D3), stimulates the breakdown of membrane phosphoinositides, generating inositol-1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) in a variety of cell systems. Several studies suggest that alterations in the receptor-mediated phosphoinositide cascade are involved in the pathophysiology of aging. Therefore, the formation of IP3 and DAG were determined under basal conditions and after stimulation with physiological concentrations of 1,25(OH)2D3 in duodenum from young (3-mo-old) and aged (24-mo-old) rats. The hormone induced a transient and biphasic formation of IP3 and DAG. Values obtained in young rats peaking at 15 s (51% and 42% above basal levels for IP3 and DAG, respectively) and at 3 min (90% and 74% above basal levels for IP3 and DAG, respectively) were significantly decreased in duodenum from senescent animals (IP3: +20% and DAG: +18% above basal level at 15 s; and IP3: +18% and DAG: +29% above basal level at 3 min). The 1,25(OH)2D3-induced generation of DAG in both young and aged duodenum was effectively inhibited in the presence of neomycin, a phospholipase C (PLC) inhibitor, and was dependent on extracellular Ca2+. After the biphasic response, the levels of DAG generated by the hormone (10 min stimulation) remained elevated; the elevation occurred in the absence of IP3 production; and the elevated levels were not abolished by neomycin, implying that phospholipids other than phosphoinositides are the source of DAG. This 1,25(OH)2D3-dependent late phase of DAG generation was also diminished in aged animals. The precise molecular basis and the physiological significance of decreased liberation of IP3 and DAG by 1,25(OH)2D3 in the aged rat duodenum remains to be determined.

Aging↗
PubMed1995

cDNA sequence identity of a vitamin D-dependent calcium-binding protein in the chick to calbindin D-9K.

1,25-dihydroxy-vitamin D3 [1,25(OH)2D3] is a steroid hormone that modulates the expression of specific proteins by a genomic mechanism of action. Calbindin D-9K is a calcium-binding protein that heretofore has only been found in mammalian tissues and whose gene expression is regulated by 1,25(OH)2D3 in a tissue specific fashion. By combined reverse transcription and polymerase chain reaction, calbindin D-9K gene expression was demonstrated for the first time to be present in several chicken tissues. Subcloning and sequencing of a partial 160 bp-cDNA PCR product revealed that the cDNA corresponds to calbindin D-9K-cDNA. This constitutes the first evidence of calbindin D-9K gene presence and expression in the avian class.

Animals↗
PubMed1994

Non-genomic signal transduction pathway of vitamin D in muscle.

The secosteroid hormone 1,25(OH)2-vitamin D3 rapidly activates voltage-dependent Ca2+ channels of the L-type in skeletal and cardiac muscle cells by a non-genomic mechanism which involves guanine nucleotide binding (G) protein-medicated stimulation of the adenylate cyclase/cAMP/protein kinase A messenger system. Modifications in calmodulin intracellular distribution induced by PKA-dependent membrane protein phosphorylation may participate in the fast regulation of muscle Ca2+ influx by 1,25(OH)2D3. The protein kinase C pathway also plays a role modulating 1,25(OH)2D3 signal transduction in muscle by cross-talk with the PKA system. The hormone sequentially activates phospholipases C and D providing diacylglycerol for PKC activation and inositol triphosphate for intracellular Ca2+ mobilization. In addition, 1,25(OH)2D3 rapidly stimulates phospholipase A2 generating arachidonic acid for the eicosanoid pathway. Specificity of hormone effects suggests that binding to a muscle membrane-bound receptor mediates these events.

Animals↗
PubMed1994

Osteolytic activity and reversal of nephrectomy-induced hypocalcemia by a fraction other than 1,25(OH)2-vitamin D3 from Solanum malacoxylon incubated with ruminal fluid.

Previous studies have shown that two lipid soluble fractions (2 and 3) isolated from Solanum malacoxylon leaf extracts incubated with ruminal fluid by Sephadex LH-20 chromatography increase intestinal P absorption and blood Ca. Fraction 2 contains 1,25(OH)2-vitamin D3, vitamin D3, 25(OH)-vitamin D3 and 1,24,25(OH)3-vitamin D3. The osteolytic activity and ability to revert nephrectomy-induced hypocalcemia of fractions 2 and 3 was compared. The tibias from 19-day-old chick embryos injected with both fractions on day 15 were shorter, lighter and had a lower ash content than those from controls. Fractions 2 and 3 also decreased dry weight and ash content in frontal bones, although only the effects of fraction 3 were statistically significant. In agreement with these observations, fraction 3 was more effective than fraction 2 to increase blood Ca levels in nephrectomized rats. Extracts from rumen samples were devoid of activity. The results support the presence of a polar derivative of 1,25(OH)2D3 in ruminal fluid-treated Solanum malacoxylon.

Animals↗
PubMed1993

1,25-Dihydroxyvitamin D-3 induces arachidonate mobilization in embryonic chick myoblasts.

1,25-Dihydroxyvitamin D-3 (1,25(OH)2D3) which activates the phospholipase C (PLC)-protein kinase C (PKC) signalling pathway, induces within 1 min a dose-dependent (10(-11)-10(-7) M) increase in the release of [3H]arachidonic acid ([3H]AA) from prelabeled embryonic chick myoblasts. The response is dependent on extracellular calcium, since it is suppressed by EGTA and nifedipine, a Ca(2+)-channel blocker, and is mimicked by the calcium ionophore A23187. 1,25(OH)2D3-induced release of [3H]AA is not affected by neomycin (0.5 mM), an inhibitor of phosphoinositide hydrolysis. 12-o-tetradecanoylphorbol-13-acetate (TPA), a PKC activator, induces an extracellular Ca(2+)-independent release of [3H]AA and amplifies the release of AA stimulated by 1,25(OH)2D3. 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H7), a PKC inhibitor, markedly suppressed TPA as well as 1,25(OH)2D3-induced [3H]AA release. Down-regulation of cellular PKC abolishes the effect of the phorbol ester, and partially inhibits 1,25(OH)2D3-induced [3H]AA release. Temporally correlated with AA liberation, the hormone increases the formation of lysophosphatidylcholine (lysoPC) and lysophosphatidylethanolamine (lysoPE) and decreases the cellular content of PC and PE. These results indicate that part of AA release by 1,25(OH)2D3 derives from PLA2 activation and that the effects of the hormone are mediated by PKC in a mode independent of phosphoinositide hydrolysis by PLC.

Animals↗
PubMed1993

Generation of inositol phosphates, diacylglycerol and calcium fluxes in myoblasts treated with 1,25-dihydroxyvitamin D3.

We have examined the effects of the seco-steroid hormone 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on membrane phosphoinositide metabolism, protein kinase C (PKC) activation and influx of extracellular Ca2+ in chick-embryo muscle-cell (myoblast) cultures. At physiological concentrations, the hormone induces a rapid (15 s) and transient release of inositol triphosphate (InsP3) and diacylglycerol (DAG). InsP3 release is maximal at 60 s (80% above controls) and then declines. The effects of 1,25(OH)2D3 on InsP3 production exhibited specificity, as 25-hydroxy-vitamin D3 and 24,25-dihydroxy-vitamin D3 did not alter myoblast InsP3 levels. The stimulation of DAG is biphasic, with peaks at 60 s (+105%) and 5 min (+700%). The second phase of DAG release is not associated with changes in InsP3. 1,25(OH)2D3 induces a rapid (within 60 s) accumulation of InsP2, and its effect on InsP is delayed (120 s). The hormone rapidly activates myoblast PKC, with maximal translocation of activity from the cytosol to the cell membrane occurring at 60 s. Myoblast 45Ca uptake significantly increases within 30 s of exposure to 1,25(OH)2D3. The response is time- (0.5-10 min) and dose- (1 pM-10 nM) dependent. The effects of the hormone are mimicked by the Ca(2+)-channel agonist Bay K 8644 and are effectively suppressed by nifedipine and extracellular EGTA. The results suggest that the rapid non-genomic actions of 1,25(OH)2D3 in myoblasts involve second-messenger systems associated with the generation of InsP3 and DAG and regulation of Ca2+ fluxes through voltage-operated channels.

Animals↗
PubMed1992

Isolation and identification of vitamin D3, 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3 and 1,24,25-trihydroxyvitamin D3 in Solanum malacoxylon incubated with ruminal fluid.

It has been shown that Solanum malacoxylon contains 1 alpha,25-dihydroxyvitamin D3-glycoside. The presence of vitamin D3 and 25-hydroxyvitamin D3 has also been suggested. In the present study vitamin D3 and three of its metabolites, including 1 alpha,25-dihydroxyvitamin D3, were detected in plant leaf extracts preincubated with ruminal fluid (SMRF). Extraction of SMRF with non-polar organic solvents and purification of the lipid extract by TLC followed by HPLC yielded nine ultraviolet-absorbing (264 nm) peaks. Four of them comigrated on a Zorbax-Sil HPLC column with synthetic standards of vitamin D3, 25-hydroxyvitamin D3, 1 alpha,25-dihydroxyvitamin D3 and 1,24R,25-trihydroxyvitamin D3, respectively. These compounds were unequivocally identified by means of mass spectrometry. The results confirm that Solanum malacoxylon contains, in addition to 1 alpha,25-dihydroxyvitamin D3, vitamin D3, 25-hydroxyvitamin D3 and possibly other as yet unidentified derivatives. As 1,24,25-trihydroxyvitamin D3 is absent in plant extracts not incubated with ruminal fluid, the data also indicate that rumen microbes may convert 1 alpha,25-dihydroxyvitamin D3 into 1,24,25-trihydroxyvitamin D3.

Animals↗
PubMed1991

Single cell analysis of changes in cytosolic calcium induced by vitamin D3 metabolites in cultured rat mesangial cells.

The acute effects of 1,25-Dihydroxy-vitamin D3 [1,25(OH)2D3] on the concentration of cytoplasmic ionized calcium [Ca2+] of cultured rat mesangial cells were studied at the single cell level by microspectrofluorometry of fura-2-loaded cells. Addition of 1,25(OH)2D3 produced an immediate increase of [Ca2]+. This rise in [Ca2+] was sustained and similar to that caused by the Ca2+ channel agonist BAY K 8644. Comparable changes were also observed in cultured human mesangial cells. The effects of the hormone (10 (-10)-10(-7) M) were dose-dependent (62% and 285%). Only 30-40% of the cells responded to stimulation with 1,25(OH)2D3. 25OHD3 also increased Ca2+ whereas 24,25(OH)2D3 and 1aOHD3 were inactive. Addition of 1 mM CoCl2 or 2-5 microM nifedipine largely blocked the effects of 1,25(OH)2D3 suggesting the involvement of Ca2+ channel activation in the rapid 1,25(OH)2D3-induced increase in mesangial cell [Ca2+]. 45Ca uptake studies are consistent with This interpretation.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1990

In vitro calcium transport properties of skeletal muscle mitochondria from vitamin D-deficient and 1,25-dihydroxy-vitamin D3-treated chicks.

Previous work has shown that vitamin D3 or 1,25-dihydroxy-vitamin D3 affect calcium content and fluxes in mitochondria of chick skeletal muscle in situ. Studies were performed to investigate whether these effects are related to variations in the Ca2+ transport properties of mitochondrial membranes. Mitochondria isolated from skeletal muscle of vitamin D-deficient chicks and chicks dosed with 1,25(OH)2D3 for 3 or 7 days (50 ng/day) were employed. No changes in the rate and affinity for calcium of the Ruthenium Red-sensitive Ca2+ uptake system were detected after treatment with 1,25(OH)2D3. The metabolite did not cause either modifications in Ca2+ efflux from mitochondria preloaded with the cation induced by Na+ or blockage of mitochondria energy supply. Prior treatment of animals with vitamin D3 was also without effects. However, a significant stimulation of Ca2- uptake by intact muscle preparations from the same experimental animals was observed in response to treatment with 1,25(OH)2D3 in vivo (50 ng/day, 3 days) or in vitro (10(-10) M, 60 minutes). In addition, the Ca content of muscle mitochondria was markedly diminished in chicks treated with the sterol. It is suggested that the effects of 1,25(OH)2D3 on muscle mitochondrial Ca metabolism may be secondary to changes in cytoplasmic Ca2+.

Animals↗
PubMed1989

Induction of specific proteins in cultured skeletal muscle cells by 1,25-dihydroxyvitamin D-3.

The presence in myoblasts of an intracellular receptor specific for 1,25-dihydroxyvitamin D-3 [1,25(OH)2D3) and 1,25(OH)2D3-dependent changes in myoblast Ca2+ transport and phospholipid metabolism which are suppressed by RNA and protein synthesis inhibitors have been shown. In agreement with these observations, incubation of chick embryo myoblasts, precultured for 24 h in a medium containing low levels of vitamin D-3 metabolites, with 1,25(OH)2D3 at conditions which induce maximum cell responses (10(-10) M, 24 h) markedly stimulated the incorporation of [3H]leucine into total cell proteins and this effect was abolished when sterol treatment was performed in the presence of cycloheximide or puromycin. To investigate whether 1,25(OH)2D3 selectively stimulates the de novo synthesis of muscle cell proteins, mixtures of myoblast proteins from control and sterol-treated cultures labelled with [14C]leucine and [3H]leucine, respectively, were separated by SDS-polyacrylamide gel electrophoresis and isoelectric focussing. Examination of 3H/14C ratios in gel fractions revealed that 1,25-(OH)2D3 stimulates the production of proteins of molecular masses (isoelectric points) of 9 kDa (4.1 and 8.5), 17 kDa (7.5), 30 kDa (7.2), 40 kDa (5.5), 55 kDa (4.5) and 100 kDa (8.6). Cell fractionation studies showed the following subcellular distribution: 9 kDa (85% cytosol, 15% microsomes); 17 and 100 kDa (100%, 1200 X g pellet); 30 kDa (65% cytosol, 35% mitochondria); 40 kDa (100% microsomes); 55 kDa (65% microsomes, 35% mitochondria). Marker enzyme data indicated that this distribution is not due to cross-contamination between fractions. Affinity chromatography of double-labelled myoblast proteins on an immobilized lectin showed that the 55 kDa protein contains carbohydrate. Labelling of myoblast proteins with 45CaCl2 after their separation on SDS-polyacrylamide gels showed in addition that the 1,25(OH)2D3-dependent proteins of 9, 17, 40 and 100 kDa are major Ca2+-binding components of the cells. Synthesis of these proteins may mediate the effects of the sterol on myoblast calcium metabolism.

Animals↗
PubMed1988

Effects of 1,25-dihydroxyvitamin D-3 on phospholipid metabolism in chick myoblasts.

1,25-Dihydroxyvitamin D-3 has been shown to increase phosphatidylcholine and decrease phosphatidylethanolamine levels of myoblasts. Recent studies have suggested that the metabolite stimulates the methylation of phosphatidylethanolamine into phosphatidylcholine. In addition, the sterol increases the arachidonate content of phosphatidylcholine. Experiments were carried out to identify the steps of muscle cell lipid metabolism affected by 1,25-dihydroxyvitamin D-3. Primary cultures of chick embryo myoblasts pretreated with physiological concentrations of 1,25-dihydroxyvitamin D-3 were labelled with [14C]ethanolamine. The sterol increased the incorporation of precursor into dimethylphosphatidylethanolamine and phosphatidylcholine, whereas it decreases the labelling of phosphatidylethanolamine. Prior treatment with cycloheximide and actinomycin D blocked these changes. 1,25-Dihydroxyvitamin D-3 also stimulated the incorporation of [14C]ethanolamine into CDP-ethanolamine. In addition, the sterol increased the incorporation of [3H]arachidonic acid into the phosphatidylcholine fraction but did not affect the incorporation of [14C]palmitic acid. The incorporation of labelled fatty acids into diacylglycerol was not changed by the sterol, whereas it stimulated incorporation of both precursors into triacylglycerol. The data indicate that 1,25-dihydroxyvitamin D-3 enhances the synthesis of phosphatidylcholine through a stimulation of de novo synthesis and methylation of phosphatidylethanolamine via a nuclear mechanism. The sterol may also increase the polyunsaturated fatty acid content of phosphatidylcholine by means of an activation of its deacylation-reacylation cycle.

Animals↗
PubMed1988

Presence of sterol-binding sites in the cytosol of French-bean (Phaseolus vulgaris) roots.

Vitamin D3 (cholecalciferol) and stigmasterol have been shown to stimulate Ca2+ uptake and to induce calmodulin synthesis in cultured French-bean (Phaseolus vulgaris) roots. In addition, the appearance of calmodulin in the cultures in response to vitamin D3 could be prevented by RNA-synthesis inhibitors. To investigate the possibility that the sterols affect root DNA transcription through a receptor-mediated mechanism, the existence of sterol-binding sites in P. vulgaris roots was investigated. Specific binding of [3H]vitamin D3 could be demonstrated with intact tissue and the cytosolic fraction obtained therefrom. Equilibrium in the binding reaction with cytosol was attained after 4 h of incubation at 0 degrees C. The [3H]vitamin D3 was reversibly bound, since it could be displaced by an excess of unlabelled sterol. An equilibrium binding constant (KD) of (3.48 +/- 0.09) x 10(-9) M and a maximum binding-site concentration (nmax) of 32 +/- 2.54 (3) pmol/mg of protein could be calculated by Scatchard [(1949) Ann. N.Y. Acad. Sci. 51, 660-672] analysis. In addition to vitamin D3, stigmasterol and sitosterol were effectively able to compete with [3H]vitamin D3 for binding to root cytosol. Cortisol, oestradiol and progesterone displaced bound labelled vitamin D3 to a lesser extent, whereas 5 beta-dihydrotestosterone, lanosterol and diosgenin were ineffective. The affinity and specificity of the root sterol-binding sites are in agreement with the characteristics of tissue responses to the sterols (Ca2+ uptake and calmodulin synthesis).

Binding Sites↗
PubMed1988

Solanum malacoxylon: a toxic plant which affects animal calcium metabolism.

The "enteque seco" is a disease of calcinosis, i.e., pathological deposition of calcium phosphate in soft tissues, which occurs in grazing cattle in Argentina and is of considerable economic importance. The ingestion of leaves of Solanum malacoxylon has been identified as the cause of the disease. Hypercalcemia and/or hyperphosphatemia and mineralization of the cardiovascular and pulmonary systems are usually seen in bovines or experimental animals exposed to this plant. The symptoms of the disease resemble those of vitamin D intoxication. In agreement with these observations, a glycoside derivative of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the hormonally active form of vitamin D in animals, has been identified as the toxic principle of S. malacoxylon. Glycoside conjugates of its precursors, 25-hydroxyvitamin D3 and vitamin D3, may also be present. Recent studies indicate that the plant factor is modified in the rumen of bovines through cleavage of the glycosidic linkage and further conversion of the released 1,25(OH)2D3 to a more polar metabolite, possibly 1,24,25-trihydroxyvitamin D3. Excess free 1,25(OH)2D3 may alter extracellular and intracellular Ca homeostasis in intoxicated animals through a receptor-mediated mechanism and activation of membrane Ca channels. In addition, 1,24,25(OH)3D3 may potentiate the effects of 1,25(OH)2D3 on intestinal Ca transport.

Animals↗
PubMed1987

Rapid changes in skeletal muscle calcium uptake induced in vitro by 1,25-dihydroxyvitamin D3 are suppressed by calcium channel blockers.

Previous investigations have shown that 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] stimulates muscle Ca uptake through a nuclear mechanism. The possibility that 1,25-(OH)2D3 would induce rapid changes in muscle Ca fluxes independent of de novo protein synthesis was investigated in the present work. In vitro preparations of soleus muscles obtained from vitamin D-deficient chicks were used. A significant increase in 45Ca labeling of the tissue was already observed after 3-min treatment with 2.4 X 10(-10) M 1,25-(OH)2D3. This early stimulation in muscle Ca uptake became maximal at 10-15 min. Cycloheximide (50 microM) did not block the effect of the metabolite at 15 and 30 min. However, the antibiotic effectively blocked the increase in Ca uptake induced by 1,25-(OH)2D3 after 1-h treatment. The rapid 1,25-(OH)2D3-dependent stimulation of 45Ca labeling of soleus muscle was not associated to changes in lipid synthesis as assessed by measurements of 3H-glycerol incorporation into the tissue lipids. However, the calcium antagonists verapamil and nifedipine (50 microM) abolished the stimulation in Ca uptake produced by 1,25-(OH)2D3 in 5 min. These results suggest that 1,25-(OH)2D3 can act directly at the muscle membrane level affecting Ca fluxes through Ca channels.

Animals↗