Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Calmodulin”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,135 records · Page 63Linked to original sources
PubMed1997

Endothelial cells and extracellular calmodulin inhibit monocyte tumor necrosis factor release and augment neutrophil elastase release.

Cultured human umbilical vein endothelial cells inhibited tumor necrosis factor-alpha release from whole blood or isolated mononuclear cells exposed to endotoxin. In contrast, the endothelial cells augmented neutrophil elastase release in the same blood. A protein with these functional properties was isolated from endothelial cell-conditioned media and, surprisingly, was identified as calmodulin. Authentic calmodulin mimicked the effect of endothelium. 125I-Calmodulin bound to a high affinity site on monocytic cell lines (Kd approximately 30 nM, in agreement with its functional activity). Cross-linking of 125I-calmodulin to monocytic cells identified a candidate calmodulin receptor. We conclude that calmodulin possesses an extracellular signaling role in addition to its intracellular regulatory functions. Calmodulin released at sites of tissue injury or possibly by specific mechanisms in the endothelium can bind to receptors, modulating the activities of inflammatory cells.

Amino Acid Sequence↗
PubMed1994

Rat myr 4 defines a novel subclass of myosin I: identification, distribution, localization, and mapping of calmodulin-binding sites with differential calcium sensitivity.

We report the identification and characterization of myr 4 (myosin from rat), the first mammalian myosin I that is not closely related to brush border myosin I. Myr 4 contains a myosin head (motor) domain, a regulatory domain with light chain binding sites and a tail domain. Sequence analysis of myosin I head (motor) domains suggested that myr 4 defines a novel subclass of myosin I's. This subclass is clearly different from the vertebrate brush border myosin I subclass (which includes myr 1) and the myosin I subclass(es) identified from Acanthamoeba castellanii and Dictyostelium discoideum. In accordance with this notion, a detailed sequence analysis of all myosin I tail domains revealed that the myr 4 tail is unique, except for a newly identified myosin I tail homology motif detected in all myosin I tail sequences. The Ca(2+)-binding protein calmodulin was demonstrated to be associated with myr 4. Calmodulin binding activity of myr 4 was mapped by gel overlay assays to the two consecutive light chain binding motifs (IQ motifs) present in the regulatory domain. These two binding sites differed in their Ca2+ requirements for optimal calmodulin binding. The NH2-terminal IQ motif bound calmodulin in the absence of free Ca2+, whereas the COOH-terminal IQ motif bound calmodulin in the presence of free Ca2+. A further Ca(2+)-dependent calmodulin binding site was mapped to amino acids 776-874 in the myr 4 tail domain. These results demonstrate a differential Ca2+ sensitivity for calmodulin binding by IQ motifs, and they suggest that myr 4 activity might be regulated by Ca2+/calmodulin. Myr 4 was demonstrated to be expressed in many cell lines and rat tissues with the highest level of expression in adult brain tissue. Its expression was developmentally regulated during rat brain ontogeny, rising 2-3 wk postnatally, and being maximal in adult brain. Immunofluorescence localization demonstrated that myr 4 is expressed in subpopulations of neurons. In these neurons, prominent punctate staining was detected in cell bodies and apical dendrites. A punctate staining that did not obviously colocalize with the bulk of F-actin was also observed in C6 rat glioma cells. The observed punctate staining for myr 4 is reminiscent of a membranous localization.

Actins↗
PubMed1996

Role of calmodulin and Spc110p interaction in the proper assembly of spindle pole body compenents.

Previously we demonstrated that calmodulin binds to the carboxy terminus of Spc110p, an essential component of the Saccharomyces cerevisiae spindle pole body (SPB), and that this interaction is required for chromosome segregation. Immunoelectron microscopy presented here shows that calmodulin and thus the carboxy terminus of Spc110p localize to the central plaque. We created temperature-sensitive SPC110 mutations by combining PCR mutagenesis with a plasmid shuffle strategy. The temperature-sensitive allele spc110-220 differs from wild type at two sites. The cysteine 911 to arginine mutation resides in the calmodulin-binding site and alone confers a temperature-sensitive phenotype. Calmodulin overproduction suppresses the temperature sensitivity of spc110-220. Furthermore, calmodulin levels at the SPB decrease in the mutant cells at the restrictive temperature. Thus, calmodulin binding to Spc110-220p is defective at the nonpermissive temperature. Synchronized mutant cells incubated at the nonpermissive temperature arrest as large budded cells with a G2 content of DNA and suffer considerable lethality. Immunofluorescent staining demonstrates failure of nuclear DNA segregation and breakage of many spindles. Electron microscopy reveals an aberrant nuclear structure, the intranuclear microtubule organizer (IMO), that differs from a SPB but serves as a center of microtubule organization. The IMO appears during nascent SPB formation and disappears after SPB separation. The IMO contains both the 90-kD and the mutant 110-kD SPB components. Our results suggest that disruption of the calmodulin Spc110p interaction leads to the aberrant assembly of SPB components into the IMO, which in turn perturbs spindle formation.

Binding Sites↗
PubMed1988

Calmodulin in normal and cystic fibrosis human intestine at different developmental stages.

Calmodulin concentrations and localisation have been analysed as a function of development in human intestinal epithelial cells from normal and cystic fibrosis individuals. In normal fetuses up to eight weeks of gestation intestinal epithelial cells which were still undifferentiated were not immunoreactive and their calmodulin content was low. From eight weeks onwards there was a significant overall increase in calmodulin content concomitant with its segregation to the apical side of epithelial cells. At 14 weeks of gestation calmodulin concentrations and localisation closely resembled those of adults. The developmental pattern of calmodulin appeared to parallel the morphological and functional maturation of brush borders which occurs during the first trimester of pregnancy. In the intestinal epithelial cells from a 19 weeks cystic fibrosis fetus and a cystic fibrosis newborn infant neither calmodulin concentration, nor its localisation were affected. Similarly, brush border calmodulin binding proteins and enzymatic activities were similar in normal subjects and the cystic fibrosis intestine.

Adult↗
PubMed2000

Regulation of a voltage-sensitive release mechanism by Ca(2+)-calmodulin-dependent kinase in cardiac myocytes.

A role for Ca(2+)-calmodulin-dependent kinase (CamK) in regulation of the voltage-sensitive release mechanism (VSRM) was investigated in guinea pig ventricular myocytes. Voltage clamp was used to separate the VSRM from Ca(2+)-induced Ca(2+) release (CICR). VSRM contractions and Ca(2+) transients were absent in cells dialyzed with standard pipette solution but present when 2-5 microM calmodulin was included. Effects of calmodulin were blocked by KN-62 (CamK inhibitor), but not H-89, a protein kinase A (PKA) inhibitor. Ca(2+) current and caffeine contractures were not affected by calmodulin. Transient-voltage relations were bell-shaped without calmodulin, but they were sigmoidal and typical of the VSRM with calmodulin. Contractions with calmodulin exhibited inactivation typical of the VSRM. These contractions were inhibited by rapid application of 200 microM of tetracaine, but not 100 microM of Cd(2+), whereas CICR was inhibited by Cd(2+) but not tetracaine. In undialyzed myocytes (high-resistance microelectrodes), KN-62 or H-89 each reduced amplitudes of VSRM contractions by approximately 50%, but together they decreased VSRM contractions by 93%. Thus VSRM is facilitated by CamK or PKA, and both pathways regulate the VSRM in undialyzed cells.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1987

Calmodulin-binding proteins in plasma membranes from adrenocortical cells.

Highly purified plasma membranes from Y-1 mouse adrenal tumor cells and those from bovine fasciculata cells were shown by [125I]iodocalmodulin overlay to contain five calmodulin-binding proteins of 240,000, 150,000, 66,000, 60,000, and 51,000 mol wt (Mr). Three of these proteins were also detected by affinity chromatography on calmodulin-Sepharose. Calmodulin binding was inhibited by competition with unlabeled calmodulin and by an inhibitor of calmodulin (trifluoperazine). Binding to each of the proteins was Ca2+ dependent. The relative proportion of binding to each of the five proteins was very different for Y-1 and bovine membranes. In Y-1 membranes as much as 50% of total binding was to the 51,000 Mr protein, whereas in bovine membranes more than 50% of binding occurred with the 150,000 Mr protein. Three of the five proteins were tentatively identified as follows: the 240,000 Mr protein is alpha-spectrin, the 60,000 Mr protein is the A subunit of the Ca2+/calmodulin-dependent protein phosphatase called calcineurin and the 51,000 Mr protein is the major subunit of a Ca2+/calmodulin-dependent protein kinase. The kinase was shown to act on specific substrates. It is concluded that calmodulin, by binding to the kinase and phosphatase, is capable of influencing the degree of phosphorylation of specific substrates in the plasma membranes of adrenal cells, and by binding to alpha-spectrin it may influence the cytoskeletons of these cells. These effects of calmodulin are likely to be important in the regulation of steroid synthesis in the adrenal cortex.

Adrenal Cortex↗
PubMed1985

The divalent cation dependence of bovine brain calmodulin-dependent phosphatase.

The divalent cation dependence of a calmodulin-stimulated phosphatase from bovine brain has been characterized kinetically using phosphorylated myelin basic protein and casein as substrates. At saturating concentrations of calmodulin, dephosphorylation of both myelin basic protein and casein was catalyzed 8- to 10-fold more rapidly at saturating concentrations of Mn2+ than at saturating concentrations of Ca2+. Half-maximal rates of dephosphorylation of both substrates occurred at either 15 microM Mn2+ or 1 microM Ca2+, and the Kact for each ion was not influenced appreciably by the presence of calmodulin. Half-maximal rates of dephosphorylation were observed at concentrations of calmodulin ranging from 3 X 10(-8) to 10(-6) M at saturating concentrations of divalent cations depending on the substrate used and the particular cation chosen. Trypsin treatment of the phosphatase activated the enzyme several-fold, eliminated its calmodulin dependence, but did not alter the Mn2+ concentration dependence of the activity. Ca2+ (10 microM) increased dephosphorylation rates without altering the Mn2+ concentration dependence of the phosphatase activity regardless of the presence of calmodulin. Mg2+ at millimolar concentrations did not alter the Ca2+ or Mn2+ concentration dependence of the activity. As measured without calmodulin, Ca2+ (90 microM) or Mn2+ (200 microM) produced nearly identical alterations of the far ultraviolet circular dichroic spectrum of the phosphatase.

Animals↗
PubMed1987

Differential reactivities of lysines in calmodulin complexed to phosphatase.

Calmodulin and calmodulin complexed with calcineurin phosphatase were trace labeled with [3H]acetic anhydride and the incorporation of [3H]acetate into each epsilon-amino lysine of calmodulin was measured. The relative reactivities of calmodulin lysines were higher in the presence of Ca2+ than in the presence of EGTA, and the order was: Lys-75 greater than Lys-94 greater than Lys-148 greater than or equal to Lys-77 greater than Lys-13 greater than or equal to Lys-21 greater than Lys-30. The changes in relative reactivity implied a change in conformation. When calmodulin was complexed with the phosphatase, Lys-21, Lys-77, and Lys-148 were most protected, implying that these residues are at or near the interaction sites or are conformationally perturbed by the interaction. Lys-30 and Lys-75 were slightly protected, lysine 13 showed no change, while lysine 94 significantly increased in reactivity. Comparison with results obtained from myosin light chain kinase using a similar technique (Jackson, A. E., Carraway, K. L., III, Puett, D., and Brew, K. (1986) J. Biol. Chem. 261, 12226-12232) reveals that calmodulin may interact with each of the two enzymes similarly at or near Lys-21, Lys-75, and Lys-148; one difference with phosphatase is that complex formation also involved Lys-77. These findings suggest that calmodulin interacts differently with its target enzymes.

Acetates↗
PubMed1984

The calmodulin-dependent activation and deactivation of the phosphoprotein phosphatase, calcineurin, and the effect of nucleotides, pyrophosphate, and divalent metal ions. Identification of calcineurin as a Zn and Fe metalloenzyme.

Studies on the interaction of calcineurin with its activator, calmodulin, showed that the 1:1 complex is the activated species. Concomitant with activation, a time-dependent deactivation of the phosphatase was observed. The process followed first order kinetics and was dependent on the presence of both Ca2+ and calmodulin. The deactivation rate constant at pH 7.6 and 30 degrees C was 0.06 min-1, which was increased by the substrate, p-nitrophenylphosphate (Km = 11 mM), to 0.47 min-1. PPi and nucleotides inhibited the enzyme competitively and accelerated the deactivation. The first order rate constant was increased to 2.3 min-1 by PPi (Ki = 55 microM) and to 8.0 min-1 by ADP (Ki = 0.94 mM). A theory dealing with the deactivation (applicable to chemical modification, etc.) of an enzyme in the absence and presence of various ligands is presented. The deactivated enzyme remained bound to calmodulin and was not reactivated by dissociation-reassociation of the calcineurin-calmodulin complex. Calcineurin was found to contain covalently bound phosphate; however, no difference in its content was detected upon deactivation, indicating that self-dephosphorylation was not involved. The deactivation could be reversed, as well as prevented, by divalent metal ions such as Ni2+ and Mn2+. Atomic absorption spectroscopy revealed nearly stoichiometric amounts of tightly bound Fe and Zn (but little other ions) on purified calcineurin, which remained bound during the calmodulin-dependent deactivation; removal of tightly bound metals is, therefore, not the cause of deactivation. Our results indicate that calcineurin is a metallophosphatase and not simply a Ca2+- and calmodulin-stimulated enzyme. In addition to the nondissociable Zn and Fe and the Ca2+ bound to the B subunit and calmodulin, the enzyme requires a divalent metal ion for structural stability and full activity.

Adenosine Diphosphate↗
PubMed1982

Calmodulin in neurotransmitter release and synaptic function.

Calmodulin is a major Ca2+-binding protein in the brain that may regulate many of the neuronal functions of Ca2+. Calmodulin was characterized in preparations of presynaptic cytoplasm and highly enriched synaptic vesicles fractions. Calmodulin regulated the Ca2+-stimulated phosphorylation of several proteins in synaptic vesicle, synaptic membrane, synaptic junction, and postsynaptic density fractions. Depolarization-dependent Ca2+ influx stimulated the phosphorylation of several synaptic proteins in whole synaptosomes, synaptic vesicles, and synaptic junctions in intact synaptosomes. Evidence is presented to demonstrate that Ca2+-calmodulin-regulated synaptic protein phosphorylation plays a role in regulating neurotransmitter release in intact synaptosome and isolated vesicle preparations. Synaptic vesicle and synaptic membrane interactions in isolated systems were mediated by Ca2+ and calmodulin, and occurred under conditions that simultaneously stimulated neurotransmitter release and protein phosphorylation. Ca2+ and calmodulin stimulated the activity of a synaptic tubulin kinase system that was shown to be a distinct enzyme system from the cyclic AMP protein kinases. The calmodulin-regulated phosphorylation of tubulin was found to cause marked alterations in the properties of tubulin, resulting in the formation of insoluble tubulin fibrils. The possible role of the tubulin kinase in converting the Ca2+ signal into a motor force at the synapse and may regulate the effects of Ca2+ on neurotransmitter release and many other aspects of synaptic activity.

Animals↗
PubMed1981

Calmodulin activates the isolated catalytic unit of brain adenylate cyclase.

The catalytic and guanine nucleotide regulatory (G/F) units of solubilized bovine brain adenylate cyclase were separated by gel filtration as described by Strittmatter, S., and Neer, E. J. ((1980) Proc. Natl. Acad. Sci. U. S. A. 77, 6344-6348). The isolated catalytic unit is activated 4 +/- 1-fold (n = 11) by pure bovine brain calmodulin and is stabilized by calmodulin against thermal inactivation. The separated G/F unit can be freed of endogenous calmodulin by gel filtration in buffer containing 1 mM EDTA and no divalent cations. The calmodulin-free G/F unit still activates the catalytic unit. Re-addition of calmodulin does not affect the rate or extent of activation of the G/F unit by guanosine 5'-(beta, gamma-imino)triphosphate. The activation by calmodulin and the G/F unit together is additive, not synergistic. These studies show that calmodulin interacts with the adenylate cyclase catalytic unit but does not seem to affect the function of the G/F unit.

Adenylyl Cyclases↗
PubMed1983

Purification and characterization of a calmodulin-dependent kinase from rat brain cytosol able to phosphorylate tubulin and microtubule-associated proteins.

Tubulin is a major substrate for endogenous Ca2+-calmodulin-dependent phosphorylation in synaptic cytoplasm. The present study details the purification to apparent homogeneity and characterization of a brain cytosolic Ca2+-calmodulin-dependent kinase which phosphorylates tubulin and microtubule-associated proteins as major substrates. The cytosolic kinase system, purified by sequential chromatography on phosphocellulose resin, calmodulin-affinity resin, and Fractogel TSK HW-55, chromatographs as a homogeneous complex of approximately 600,000 Da on Sephacryl S-300. This calmodulin-dependent kinase possesses a group of properties which specifically characterize this enzyme system: 1) the enzyme contains two calmodulin-binding doublets, rho and sigma, of approximately 52,000 and 63,000 Da, respectively; 2) both the rho and the sigma subunits demonstrate isoelectric points between 6.7 and 7.2; 3) both the rho and sigma subunits demonstrate autophosphorylation; 4) both the rho and sigma subunits show significant homologies as assessed by tryptic peptide fingerprints; 5) in the absence of substrate, both the rho and sigma subunits manifest lower mobility autophosphorylated species; 6) the kinase phosphorylates beta-tubulin equally on threonine and serine residues. Substrate specificity, kinetic parameters, calmodulin-binding properties, subunit composition, and subunit isoelectric points clearly differentiate this enzyme from other previously reported calmodulin-dependent kinases.

Animals↗
PubMed1994

Myosin I from mammalian smooth muscle is regulated by caldesmon-calmodulin.

A single-headed monomeric myosin (myosin I) was isolated from pig urinary bladder smooth muscles and purified to homogeneity. Myosin I from smooth muscle is composed of a 110-kDa heavy chain and three 17-kDa light chains. The heavy chain from smooth muscle myosin I does not cross-react with the antibody against conventional myosin (myosin II) from smooth muscle, but it does show antigenic similarity to adrenal medulla myosin I heavy chain. The light chain from smooth muscle myosin I is similar to calmodulin in molecular weight, amino acid composition, and migration on SDS-polyacrylamide gel electrophoresis in the presence of Ca2+. The high salt ATPase activity of myosin I in the presence of CaCl2 is higher than that in K(+)-EDTA. Smooth muscle actin causes a 5-10-fold activation of the Mg-ATPase activity of myosin I. In the presence of Ca2+, exogenous calmodulin enhances the actin-activated ATPase activity of myosin I, and the increased activity is associated with the binding of exogenous calmodulin to myosin I heavy chain. A maximum of 4 mol of light chains/mol of myosin I heavy chain is observed in the presence of exogenous calmodulin. Caldesmon, a calmodulin/actin-binding protein, inhibits the actin-activated ATPase activity of myosin I. This inhibition is reversed by exogenous calmodulin in the presence of Ca2+. The actin activation of myosin I ATPase exhibits around 50% Ca2+ sensitivity in the presence of exogenous calmodulin. When caldesmon is bound to actin, Ca2+ sensitivity is increased to 80% in the presence of calmodulin. Therefore, smooth muscle caldesmon, which is thought to play a role in the regulation of actin activation of myosin II, also regulates the actin activation of myosin I ATPase in smooth muscle.

Actins↗
PubMed1998

Effects of calmodulin inhibitors on cyprid larvae of the barnacle, Balanus amphitrite.

During our study on signal transduction systems involved in larval settlement and metamorphosis of the barnacle Balanus amphitrite, we could detect calmodulin, a major intracellular calcium-binding protein, in both cyprids and adult barnacles using immunoblot technique. In order to examine roles of calmodulin in larval settlement and metamorphosis, we examined the effects of calmodulin inhibitors involved in phosphodiesterase (PDE), myosin light chain kinase (MLCK), calmodulin kinase II (CaM-II) on cyprids. Calcium-calmodulin-dependent PDE inhibitors inhibited larval attachment and metamorphosis in a dose-dependent manner. In contrast, cyclic AMP (cAMP)-dependent PDE inhibitors promoted larval attachment and metamorphosis, while cyclic GMP (cGMP)-dependent PDE inhibitors did not show such effect. Thus, PDE activity may depend on cAMP rather than calmodulin or cGMP in promotion of larval attachment and metamorphosis. Moreover, calmodium inhibitors involved in MLCK or CaM-II inhibited larval behaviors for attachment and metamorphosis. These results suggest that calmodulin, which is present in both adult barnacles and cyprids, may be involved in enzyme reactions such as MLCK or CaM-II rather than PDE in B. amphitrite cyprids.

Animals↗
PubMed1998

Identification and characterization of the KlCMD1 gene encoding Kluyveromyces lactis calmodulin.

The KlCMD1 gene was isolated from a Kluyveromyces lactis genomic library as a suppressor of the Saccharomyces cerevisiae temperature-sensitive mutant spc110-124, an allele previously shown to be suppressed by elevated copy number of the S. cerevisiae calmodulin gene CMD1. The KlCMD1 gene encodes a polypeptide which is 95% identical to S. cerevisiae calmodulin and 55% identical to calmodulin from Schizosaccharomyces pombe. Complementation of a S. cerevisiae cdm1 deletion mutant by KlCMD1 demonstrates that this gene encodes a functional calmodulin homologue. Multiple sequence alignment of calmodulins from yeast and multicellular eukaryotes shows that the K. lactis and S. cerevisiae calmodulins are considerably more closely related to each other than to other calmodulins, most of which have four functional Ca2+-binding EF hand domains. Thus like its S. cerevisiae counterpart Cmd1p, the KlCMD1 product is predicted to form only three Ca2+-binding motifs.

Amino Acid Sequence↗
PubMed1996

The linker of calmodulin lacking Glu84 is elongated in solution, although it is bent in the crystal.

The solution structure of a mutant calmodulin (des84) lacking Glu84 in the central helix linking the two calmodulin lobes is substantially different from its crystal structure. As determined by small-angle X-ray scattering, the radius of gyration and the maximum linear dimension of des84 in the presence of 0.1 mM calcium are 20.8 A and 62.5 A, respectively. These respective dimensions are larger than those expected from the crystal structure of des84, 18.5 A and 55.0 A, and smaller than those expected from the crystal structure of wild type, 22.8 A and 67.5 A. The distance distribution function of des84 indicates that it assumes an elongated, dumbbell shape in solution. The solution scattering profile of des84 is indistinguishable from that of wild-type calmodulin. The calcium-dependent binding of melittin to des84 causes a change in its shape from elongated to spherical, as seen with other calmodulins. In comparison with calcium-saturated des84, calcium-free des84 is slightly elongated; a slight compaction is observed with native calmodulin. The observed differences between the averaged solution structure and the crystal structure of des84 suggests that an ensemble of structures is available to calmodulin in solution and that its target need not induce a change in its conformation. These results support the theory that the linker region of the central helix of calmodulin functions as a flexible tether.

Calcium↗
PubMed2001

Quantitative imaging of tyrosine hydroxylase and calmodulin in the human brain.

The distributions of tyrosine hydroxylase and calmodulin in adult normal postmortem human brain were analyzed quantitatively. Consecutive coronal sections were obtained from the anterior area of the right hemisphere and were stained immunohistochemically for tyrosine hydroxylase and calmodulin. Stained sections were divided into approximately 3 million microareas at 50 microm intervals, and the immunohistochemical fluorescence intensity in each area was measured by a human brain mapping analyzer, which is a microphotometry system for analysis of the distribution of neurochemicals in a large tissue slice. Immunoreactive staining of tyrosine hydroxylase and calmodulin was observed in almost all brain regions, but its intensity varied. Relatively high levels of calmodulin were observed in brain regions with high levels of tyrosine hydroxylase, though high levels of tyrosine hydroxylase were not always observed in brain regions where high levels of calmodulin were distributed. In particular, high levels of both of tyrosine hydroxylase and calmodulin were distributed in the caudate nucleus and putamen. Previously it was shown that tyrosine hydroxylase was activated and dopamine synthesis was enhanced in the neostriatum region in mice and rats by the intracerebroventricular administration of calcium through a calmodulin-dependent system. The present results combined with these previous findings suggest that the activity of tyrosine hydroxylase in the caudate nucleus and putamen of humans may also be regulated by a calcium/calmodulin-dependent system.

Aged↗
PubMed1994

Calmodulin immunoreactivity in the chicken pineal gland: comparison with calbindin-D28k, calretinin, and S100.

Calmodulin distribution in the chicken pineal organ was investigated by immunohistochemistry. Calmodulin immunoreactivity was detected in ependymocytes in the follicular zone and in interstitial cells in the parafollicular zone. No calmodulin immunoreactivity was detected in pinealocytes. Lack of calmodulin immunoreactivity in pinealocytes raises questions about its proposed function in melatonin synthesis as suggested by pharmacological studies using calmodulin antagonists. The calmodulin distribution was comparable to that of S100, a glial cell marker. Two other markers, calbindin-D28k and calretinin, which in neuroanatomical studies give excellent cytoarchitectonic staining, in the chick pineal permitted the detection of two subclasses of pinealocytes. One was darkly stained by calbindin-D28k and rare. The other was very abundant and calretinin positive. In the parafollicular zone, calbindin-D28k and/or calretinin antibodies allowed us to visualize cells presenting a neuron-like morphology. Calretinin immunoreactivity was detected in nearly all pinealocytes in which hydroxy-indol-O-methyl transferase was also located. Comparison between the lack of calmodulin and the presence of calretinin, belonging to the same calcium-binding protein family, in chick pinealocytes raises the hypothesis about a possible role of calretinin in melatonin synthesis.

Animals↗