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 145 records · Page 8Linked to original sources
PubMed1996

Interaction of calmodulin-binding domain peptides of nitric oxide synthase with membrane phospholipids: regulation by protein phosphorylation and Ca(2+)-calmodulin.

Endothelial nitric oxide synthase (eNOS) is unique among the NO synthase isozymes in being modified with myristoyl group, which appears to be necessary for its membrane association. However, the presence of myristoylated eNOS in cytosolic fraction after the stimulation-dependent translocation of the enzyme from membrane to cytosol suggests that other regions may be involved in the eNOS-membrane interaction and its regulation. In this study, we have synthesized a 20-amino acid peptide corresponding to the putative calmodulin-binding domain of human eNOS and studied the interaction of the peptide with calmodulin and with various membrane phospholipids. The peptide formed a stoichiometric complex with calmodulin. Upon addition of various acidic phospholipids, the peptide showed a drastic conformational change from random coil to alpha-helix, as was evidenced by circular dichroism spectroscopy. These results suggest that the same domain of eNOS binds both calmodulin and membrane phospholipids. Furthermore, we found that the synthetic peptide was phosphorylated in vitro by protein kinase C. Phosphorylation of the peptide decreased its interaction with membrane phospholipids. Thus, our results raise the possibility that the calmodulin-binding domain is directly involved in the membrane association of eNOS and that phosphorylation of the domain and Ca(2+)-calmodulin may regulate the interaction. Synthetic peptides corresponding to the calmodulin-binding domains of macrophage and neuronal isozymes showed similar abilities to bind phospholipids, suggesting that the calmodulin-binding domains of NO synthase serve as the phospholipid-binding domains as well.

Amino Acid Sequence↗
PubMed1984

Identification of the major postsynaptic density protein as homologous with the major calmodulin-binding subunit of a calmodulin-dependent protein kinase.

The major postsynaptic density protein (mPSDp), comprising greater than 50% of postsynaptic density (PSD) protein, is an endogenous substrate for calmodulin-dependent phosphorylation as well as a calmodulin-binding protein in PSD preparations. The results in this investigation indicate that mPSDp is highly homologous with the major calmodulin-binding subunit (p) of tubulin-associated calmodulin-dependent kinase (TACK), and that PSD fractions also contain a protein homologous with the sigma-subunit of TACK. Homologies between mPSDp and a 63,000 dalton PSD protein and the rho- and sigma-subunits of TACK were established by the following criteria: (1) identical apparent molecular weights; (2) identical calmodulin-binding properties; (3) manifestation of Ca2+-calmodulin-stimulated autophosphorylation; (4) identical isoelectric points; (5) identical calmodulin binding and autophosphorylation patterns on two-dimensional gels; (6) homologous two-dimensional tryptic peptide maps; and (7) similar phosphoamino acid-specific phosphorylation of tubulin. The results suggest that mPSDp is a calmodulin-binding protein involved in modulating protein kinase activity in the postsynaptic density and that a tubulin kinase system homologous with TACK exists in a membrane-bound form in the PSD.

Animals↗
PubMed1985

Identification of naturally occurring calmodulin inhibitors in plants and their effects on calcium- and calmodulin-promoted protein phosphorylation.

While studying the calmodulin activity in post-climacteric apples, a heat stable, dialyzable component that inhibited calmodulin-promoted phosphodiesterase activity was detected. The compound(s) that inhibited calmodulin activity did not bind to Dowex-50, H+ or Dowex-2, Cl- and was exclusively present in the neutral fraction. The inhibitors irreversibly bound to polyvinylpolypyrrolidone indicating their phenolic nature. Fractionation of the neutral fraction on a C18-microbondapak column and analysis for the inhibition of calmodulin-promoted phosphodiesterase activity showed significant inhibitory activity associated with fractions eluted 5 min, 15 min and 18 min after injection. Perdeuteriomethylation and combined gas chromatographic-mass spectrometric analysis of the inhibitors showed them to be flavonoids. (+)-Catechin was identified in the fraction eluted 5 min after injection that also showed maximum inhibition. Other flavonoids such as epicatechin, quercetin and naringenin also inhibited calmodulin-promoted phosphodiesterase activity. Among the phenolic compounds commonly encountered in plant tissue only caffeic acid inhibited calmodulin-promoted phosphodiesterase activity. Inhibition by catechin and caffeic acid could be reversed by increasing the calmodulin concentration in the assay mixture. Both catechin and caffeic acid inhibited Ca- and calmodulin-promoted phosphorylation of soluble proteins from corn coleoptiles. The physiological properties of flavonoids are discussed in light of this evidence.

Antioxidants↗
PubMed1987

Characterization of the calmodulin-binding sites of muscle phosphofructokinase and comparison with known calmodulin-binding domains.

Calmodulin has been shown to interact with high affinity with muscle phosphofructokinase (Mayr, G. W. (1984) Eur. J. Biochem. 143, 513-520, 521-529). In this study, direct binding measurements indicated that each of the two subunits of dimeric phosphofructokinase bound two calmodulins with Kd values of about 3 nM and 1 microM, respectively, in a strictly Ca2+-dependent way. To get more detailed information about this interaction, calmodulin-binding fragments were isolated from a CNBr digest of phosphofructokinase using affinity chromatography on calmodulin-agarose. Two fragments, M11 (Mr 3080) and M22 (Mr 8060), formed a 1:1 stoichiometric complex with Ca2+-calmodulin. The amino acid sequences of these fragments were determined, and their positions in the three-dimensional structure-model of phosphofructokinase are proposed. Fragment M11, which binds to calmodulin with the higher affinity (Kd 11.4 nM), is located in a region of the subunit where two dimers have been proposed to make contacts if associating to active tetrameric enzyme. A stabilization of the dimeric form of the enzyme by binding of calmodulin supports this location of M11. The weaker binding fragment M22 (Kd 198 nM) corresponds to the C-terminal part of the polypeptide and contains the site which is phosphorylated by cAMP-dependent protein kinase. Both fragments have structural properties in common with the isolated calmodulin-binding domains of myosin light chain kinase: two cationic segments rich in hydrophobic residues, one constantly possessing a tryptophan, and the other exhibiting an amino acid sequence resembling sites phosphorylated by cAMP-dependent protein kinase.

Amino Acid Sequence↗
PubMed1982

Characterization of calmodulin and calmodulin isotypes from sea urchin gametes.

Procedures were developed for the purification of calmodulin from the eggs and from the sperm of the sea urchin Strongylocentrotus purpuratus and Arbacia punctulata. Two forms of calmodulin were isolated from A. punctulata eggs, one from each of the other three sources. All five calmodulins are similar to vertebrate calmodulin as judged by their activation of bovine brain cyclic nucleotide phosphodiesterase, calcium-dependent interaction with troponin I and with chloropromazine, increased anode mobility on sodium dodecyl sulfate gels in the presence of calcium, cross-reactivity with anti-vertebrate calmodulin antibodies and amino acid compositions including the presence of a single residue of trymethyllysine. The two forms of calmodulin from A. punctulata eggs, calmodulin A and calmodulin B, can be distinguished from one another on the basis of DEAE-cellulose chromatography, amino acid analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence or absence of calcium and competitive radioimmunoassays. There is no evidence that either form is a proteolytic product of the other.

Amino Acids↗
PubMed1993

Modification of the calcium and calmodulin sensitivity of the type I adenylyl cyclase by mutagenesis of its calmodulin binding domain.

The type I adenylyl cyclase is directly stimulated by Ca2+ and calmodulin in vitro, and the enzyme is also stimulated by increases in intracellular Ca2+ in vivo. Ca2+ stimulation of the enzyme in vivo may be due to direct interactions of the enzyme with Ca2+ and calmodulin or to an indirect mechanism involving stimulation of the enzyme by Ca(2+)-activated protein kinases. In this study, we have made several point mutations within the calmodulin binding domain to determine if the Ca2+ sensitivity of the enzyme can be modified by mutagenesis. The catalytic activities of the mutant enzymes were comparable to wild type type I adenylyl cyclase. Substitution of Cys-507 with Ser-507 did not have significant effects on the calmodulin or Ca2+ sensitivity of the enzyme. However, replacement of Lys-504 with Asp caused a 4-fold decrease in sensitivity to Ca2+. Ca2+ and calmodulin stimulation were abolished by substitution of Phe-503 with Arg-503. Stimulation of type I adenylyl cyclase activity in vivo by intracellular Ca2+ was also greatly diminished with the Arg-503 mutant indicating that Ca2+ stimulation of the enzyme in vivo is due primarily to direct interactions with calmodulin and Ca2+. These data demonstrate that the Ca2+ sensitivity of this enzyme can be modulated by point mutagenesis within the putative calmodulin binding domain and indicate that the enzyme can be directly regulated by Ca2+ and calmodulin in vivo.

Adenylyl Cyclases↗
PubMed1996

Calmodulin content in pancreatic islets and the response of islet membrane Ca2+ ATPase to calmodulin in phosphate depletion.

Chronic phosphate depletion is associated with a reduced Vmax of Ca2+ ATPase in many cells. The mechanisms underlying this phenomenon are not fully understood. One of the regulators of the Ca2+ ATPase enzyme is calmodulin, and the reduced availability of calmodulin or impaired interaction between it and Ca2+ ATPase could be responsible for the impaired activity of this enzyme in phosphate depletion. The present study examined the calmodulin content of pancreatic islets and the effect of calmodulin on the Vmax of Ca2+ ATPase in islets harvested from phosphate-depleted (PD) and pair-weighed (PW) rats. The calmodulin contents in islets from the 2 groups of animals were not different. Basal levels of Vmax of Ca2+ ATPase of islets from PD rats were significantly (p < 0.01) lower than in PW rats. Calmodulin produced a significant (p < 0.01) increase in Vmax of Ca2+ ATPase in islets of PW rats but failed to do so in islets of PD rats. The results indicate that the impaired activity of Ca2+ ATPase in islets of PD rats is not due to the reduced availability of calmodulin but an impaired response of the enzyme to calmodulin is at least partly responsible for the reduction in the Vmax of the enzyme.

Adenosine Triphosphate↗
PubMed1994

Expression of calmodulin and calmodulin binding proteins in lymphoblastoid cells.

Calmodulin is encoded in vertebrates by three different genes: CALM1, CALM2, and CALM3. We have examined the mRNAs expressed from these three genes in eight lines of human lymphoblastoid cells (Namalwa, Raji, Ramos, JY, Molt-4, Jurkat, CEM, and HPB-ALL). We found that all these cell lines (except Ramos) overexpressed CALM3 transcripts, which led to an increase of total CaM protein with respect to quiescent normal T lymphocytes. The nuclear concentration of calmodulin was measured in two of these lymphoblastoid cell lines (JY and HPB-ALL) and compared to quiescent and phytohemagglutinin-activated T lymphocytes. Activated lymphocytes showed a 2-fold increase of nuclear calmodulin with respect to quiescent cells, whereas in the two lymphoblastoid cell lines, nuclear calmodulin remained similar to that of quiescent cells. The levels of a calmodulin-binding protein of 150 kDa in the homogenates of the eight lymphoblastoid lines was found to be higher than those of quiescent and activated lymphocytes. Likewise, the amount of three calmodulin-binding proteins of 240, 200, and 170 kDa was also increased in several of the cell lines, but not in all of them. The 170-kDa protein was only expressed by activated lymphocytes and lymphoblastoid cells, suggesting that it could be specific for proliferating cells. In the nuclei of activated lymphocytes and lymphoblastoid cells, a decrease of a calmodulin-binding protein of 110 kDa and increases of three other of 240, 180 and 170 kDa were also detected.

Animals↗
PubMed1984

CAPP-calmodulin: a potent competitive inhibitor of calmodulin actions.

A covalent adduct of norchlorpromazine (CAPP) and calmodulin is a very potent antagonist of calmodulin activation of several enzymes. The phenothiazine-calmodulin complex (CAPP-calmodulin) acts as a pure antagonist with phosphodiesterase and myosin kinase or a partial agonist with the phosphoprotein phosphatase, calcineurin. Because of its potency and the selectivity inherent to its calmodulin moiety, CAPP-calmodulin should be a uniquely useful probe of calmodulin actions.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1994

Calmodulin function and calmodulin-binding proteins during autoactivation and spore germination in Dictyostelium discoideum.

Dictyostelium discoideum spores can be activated to initiate germination either endogenously via a diffusible autoactivator, or exogenously via heat. Following activation, three successive stages of germination occur, the lag stage, spore swelling and amoebal emergence. A previous study [Lydan M. A. and Cotter D. A. (1994) FEBS Lett. 115, 137-142] has shown that spore swelling is dependent on the activity of calmodulin. In this study, the calmodulin antagonists trifluoperazine and calmidazolium inhibited autoactivation, but had no effect upon heat activation. These agents also inhibited amoebal emergence following either form of activation. The effects caused by the anti-calmodulin agents were specific to an inhibition of calmodulin function since agents which modulate the activity of protein kinase C had no effect upon spore germination. A calcium-dependent calmodulin-binding protein of about 64,000 M(r) may be associated with the process of autoactivation since it was only seen in those spores which respond to the autoactivator. Overall, this study provides evidence to show that calmodulin plays a regulatory role during autoactivation and amoebal emergence during spore germination in D. discoideum and provides evidence for the calmodulin-dependent mechanisms which mediate each of these phases of germination.

Animals↗
PubMed1988

Synthetic peptides based on the calmodulin-binding domain of myosin light chain kinase inhibit activation of other calmodulin-dependent enzymes.

Nanomolar concentrations of synthetic peptides corresponding to the calmodulin-binding domain of skeletal muscle myosin light chain kinase were found to inhibit calmodulin activation of seven well-characterized calmodulin-dependent enzymes: brain 61 kDa cyclic nucleotide phosphodiesterase, brain adenylate cyclase, Bordetella pertussis adenylate cyclase, red blood cell membrane Ca++-pump ATPase, brain calmodulin-dependent protein phosphatase (calcineurin), skeletal muscle phosphorylase b kinase, and brain multifunctional Ca++ (calmodulin)-dependent protein kinase. Inhibition could be entirely overcome by the addition of excess calmodulin. Thus, the myosin light chain kinase peptides used in this study may be useful antagonists for studying calmodulin-dependent enzymes and processes.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1991

Fluorescence analysis of calmodulin mutants containing tryptophan: conformational changes induced by calmodulin-binding peptides from myosin light chain kinase and protein kinase II.

Peptide-induced conformational changes in five isofunctional mutants of calmodulin (CaM), each bearing a single tryptophan residue either at the seventh position of each of the four calcium-binding loops (i.e., amino acids 26, 62, 99, and 135) or in the central helix (amino acid 81) were studied by using fluorescence spectroscopy. The peptides RS20F and RS20CK correspond to CaM-binding amino acid sequence segments of either nonmuscle myosin light chain kinase (nmMLCK) or calmodulin-dependent protein kinase II (CaMPK-II), respectively. Both steady-state and time-resolved fluorescence data were collected from the various peptide-CaM complexes. Steady-state fluorescence intensity measurements indicated that, in the presence of an excess of calcium, both peptides bind to the calmodulin mutants with a 1:1 stoichiometry. The tryptophans located in loops I and IV exhibited red-shifted emission maxima (356 nm), high quantum yields (0.3), and long average lifetimes (6 ns). They responded in a similar manner to peptide binding, by only slight changes in their fluorescence features. In contrast, the fluorescence intensity of the tryptophans in loops II and III decreased markedly, and their fluorescence spectrum was blue-shifted upon peptide binding. Analysis of the tryptophan fluorescence decay of the last mentioned calmodulins supports a model in which the equilibrium between two (Trp-99) or three (Trp-62) states of these tryptophan residues, each characterized by a different lifetime, was altered toward the blue-shifted short lifetime component upon peptide binding. Taken together, these data provide new evidence that both lobes of calmodulin are involved in peptide binding. Both peptides induced similar changes in the fluorescence properties of the tryptophan residues located in the calcium-binding loops, with the exception of calmodulin with Trp-135. For this last mentioned calmodulin, slight differences were observed. Tryptophan in the central helix responded differently to RS20F and RS20CK binding. RS20F binding induced a red-shift in the emission maximum of Trp-81 while RS20CK induced a blue-shift. The quenching rate of Trp-81 by iodide was slightly reduced upon RS20CK binding, while RS20F induced a 2-fold increase. These results provide evidence that the environment of Trp-81 is different in each case and are, therefore, consistent with the hypothesis that the central helix can play a differential role in the recognition of, or response to, CaM-binding structures.

Amino Acid Sequence↗
PubMed1985

Differential regulation of bovine brain calmodulin-dependent cyclic nucleotide phosphodiesterase isoenzymes by cyclic AMP-dependent protein kinase and calmodulin-dependent phosphatase.

Purified bovine brain calmodulin-dependent cyclic nucleotide phosphodiesterase (3',5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) contains isozymes that are composed of two distinct subunits with molecular masses of 60,000 and 63,000 daltons. Analysis by NaDodSO4 gel electrophoresis and autoradiography of a phosphodiesterase sample phosphorylated in the presence of [32P]ATP and bovine heart cAMP-dependent protein kinase catalytic subunit revealed that only the 60-kDa subunit was phosphorylated. By using an isozyme preparation greatly enriched with the 60-kDa subunit, the following observations regarding the subunit phosphorylation were made. First, the phosphorylation resulted in the maximal incorporation of about 2 mol of phosphate per mol of subunit. Second, complete inhibition of 60-kDa subunit phosphorylation was approached at a saturating concentration of Ca2+ when a molar ratio of calmodulin to phosphodiesterase of 2:1 was used. No inhibition was observed in the presence of either Ca2+ or calmodulin alone. Third, the phosphorylation was accompanied by a decrease in the enzyme affinity for calmodulin; calmodulin concentrations required for 50% activation of nonphosphorylated and maximally phosphorylated phosphodiesterase isozyme samples were 0.51 and 9.3 nM, respectively. Fourth, the phosphodiesterase isozyme could be dephosphorylated by the calmodulin-dependent phosphatase (calcineurin) in the presence of Ni2+ or Mn2+, the dephosphorylation being associated with an increase in the enzyme affinity for calmodulin. Fifth, peak II rabbit liver phosphoprotein phosphatase catalytic unit did not catalyze the dephosphorylation of the phosphodiesterase isozyme.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1999

Identification of the calmodulin-binding domain of neuron-specific protein kinase C substrate protein CAP-22/NAP-22. Direct involvement of protein myristoylation in calmodulin-target protein interaction.

Various proteins in the signal transduction pathways as well as those of viral origin have been shown to be myristoylated. Although the modification is often essential for the proper functioning of the modified protein, the mechanism by which the modification exerts its effects is still largely unknown. Brain-specific protein kinase C substrate, CAP-23/NAP-22, which is involved in the synaptogenesis and neuronal plasticity, binds calmodulin, but the protein lacks any canonical calmodulin-binding domain. In the present report, we show that CAP-23/NAP-22 isolated from rat brain is myristoylated and that the modification is directly involved in its interaction with calmodulin. Myristoylated and non-myristoylated recombinant proteins were produced in Escherichia coli, and their calmodulin-binding properties were examined. Only the former bound to calmodulin. Synthetic peptides based on the N-terminal sequence showed similar binding properties to calmodulin, only when they were myristoylated. The calmodulin-binding site narrowed down to the myristoyl moiety together with a nine-amino acid N-terminal basic domain. Phosphorylation of a single serine residue in the N-terminal domain (Ser5) by protein kinase C abolished the binding. Furthermore, phosphorylation of CAP-23/NAP-22 by protein kinase C was also found myristoylation-dependent, suggesting the importance of myristoylation in protein-protein interactions.

Amino Acid Sequence↗
PubMed1995

Calbindin28kDa and calmodulin are hyperabundant in rat dental enamel cells. Identification of the protein phosphatase calcineurin as a principal calmodulin target and of a secretion-related role for calbindin28kDa.

Enamel cells are likely to experience heavy demands for intracellular calcium homeostasis during the secretion and hypermineralization of dental enamel. Here, the two major high-affinity calcium-binding proteins in rat enamel epithelium were identified as calbindin28kDa and calmodulin, using a microscale approach. Both proteins were hyperabundant, totalling up to 2% of the soluble protein and surpassing the amounts in cerebellum, the benchmark tissue. Calbindin28kDa and calmodulin accounted for 26% of the total calcium-binding capacity in enamel cell cytosol, under near physiological conditions. Numerous calmodulin-binding proteins were detected with an overlay assay, indicating that calmodulin has multiple major targets in enamel cells. The calcium/calmodulin-regulated protein phosphatase, calcineurin, was identified as a principal calmodulin target constituting 0.1% of the soluble protein. Calmodulin and calcineurin were expressed constitutively, implying continued heavy usage of calcium/calmodulin-based and phosphorylation-based signalling events throughout enamel cell development. Calbindin28kDa, in contrast, was expressed at fourfold higher levels in secretion-phase cells than during the calcium-intensive hypermineralization phase, unexpectedly pointing to an important role associated with secretion. Supporting this notion, immunoblots revealed that 33% of total (SDS-soluble) calbindin28kDa was in the particulate fraction and predominantly associated with the Triton-insoluble cytoskeleton. Solubilisation of cytoskeletal calbindin28kDa required high concentrations of NaCl or urea, indicating the existence of a high-affinity target ligand. The unusual abundance of calmodulin, calbindin28kDa and calcineurin demonstrated here provides the first molecular evidence that enamal cells possess a strong capability for intracellular calcium homeostasis. Since none of these proteins was up-regulated during enamel hypermineralization, it appears that other calcium-binding proteins are primarily involved in the putative transcellular passage of calcium.

Animals↗
PubMed1997

Introduction of a phosphate at serine741 of the calmodulin-binding domain of the neuronal nitric oxide synthase (NOS-I) prevents binding of calmodulin.

The calmodulin-binding domain of neuronal nitric oxide synthase (NOS-I) is represented by a segment of 26 amino acids. We tested whether the phosphorylation of a serine in the calmodulin-binding domain changes the affinity of calmodulin for this binding site. We monitored the binding of calmodulin to synthetic peptides by surface plasmon resonance spectroscopy, an electrophoretic mobility assay, circular dichroism spectroscopy and competitive inhibitory studies. All four experimental approaches showed that binding of calmodulin to the calmodulin-binding site is blocked by introduction of a phosphate. Phosphorylation of the calmodulin-binding domain of NOS-I could be a negative feedback loop to turn off NOS-I activity.

Amino Acid Sequence↗
PubMed1996

The receptor-associated protein (RAP) binds calmodulin and is phosphorylated by calmodulin-dependent kinase II.

The receptor-associated protein, RAP, is an intracellular protein that may function as a chaperone for the LDL-receptor family receptors. Here we report calmodulin as the first identified RAP binding protein outside of the LDL-receptor family members. We demonstrate that RAP binds calmodulin in a Ca2+- and pH-dependent manner characteristic of calmodulin-dependent enzymes, and present evidence that RAP is a substrate for calmodulin-dependent enzymes. Thus, CaM-kinase II and calcineurin readily phosphorylate and dephosphorylate, respectively, serine residues in RAP, and in the individual RAP domains D2 (amino acids 113-218) and D3 (amino acids 219-323) which both contain sites for CaM-kinase II-mediated phosphorylation and for calmodulin binding. In addition, we provide evidence that RAP is phosphorylated by other kinases such as casein kinase II. Studies of 32[ortho]P-labelled cell cultures demonstrate that RAP is phosphorylated in vivo. Our results suggest that RAP may have hitherto unknown functions implicating phosphorylation and calmodulin-mediated modulation.

Amino Acid Sequence↗
PubMed1983

Effect of calcium-antagonist and calmodulin-antagonist drugs on calmodulin-dependent contractions of chemically skinned vascular smooth muscle from rabbit renal arteries.

1. Renal arteries from rabbits were chemically skinned by incubation with Triton X-100, and subsequently stored in buffered glycerol. 2. In the presence of Mg-ATP, of EGTA-buffered calcium, and of calmodulin, miniature strips of the skinned arteries developed tension the strength of which was approx. 15-20% of that of viable renal arteries. 3. Tension development was dependent on the concentration of both calcium and calmodulin. 4. The effect of eight vasodilator drugs, the majority of them being "calmodulin antagonists" or "calcium antagonists", on the skinned arteries was assessed. In concentrations up to 10(-3) M, verapamil, D-600, and hydralazine proved to be ineffective, and the same was found with the dihydropyridine derivatives, nifedipine and felodipine, at 0.6 X 10(-3) M and 0.8 X 10(-4) M, respectively, i.e. at saturation in a 9:1 contracting buffer/ethanol mixture (v/v). 5. In a concentration-dependent manner, trifluoperazine, W-7, and fendiline relaxed Ca-calmodulin-induced tension or prevented tension development when given prior to the activation by Ca-calmodulin. However, considerably higher concentrations of the drugs were necessary for half-maximal relaxation than the reported concentrations for half-maximal saturation of hydrophobic binding sites at the calmodulin molecule. 6. These findings suggest that at therapeutic blood levels, the vasodilator properties of calcium antagonists and other direct vasodilators cannot be explained by interference with the binding of myosin light chain kinase to calmodulin.

Animals↗