Inhibition of calmodulin-dependent and independent cardiac sarcoplasmic reticulum activities by R24571

CaMKII and CaMKIV mediate distinct prosurvival signaling pathways in response to depolarization in neurons

By fusing the CaMKII-inhibitory peptide AIP to GFP, we constructed a specific and effective CaMKII inhibitor, GFP-AIP. Expression of GFP-AIP and/or dominant-inhibitory CaMKIV in cultured neonatal rat spiral ganglion neurons (SGNs) shows that CaMKII and CaMKIV act additively and in parallel to mediate the prosurvival effect of depolarization. Depolarization or expression of constitutively active CaMKII functionally inactivates Bad, indicating that this is one means by which CaMKII promotes neuronal survival. CaMKIV, but not CaMKII, requires CREB to promote SGN survival, consistent with the exclusively nuclear localization of CaMKIV and indicating that the principal prosurvival function of CaMKIV is activation of CREB. Consistent with this, a constitutively active CREB construct that provides a high level of CREB activity promotes SGN survival, although low levels of CREB activity did not do so. Also, in apoptotic SGNs, activation of CREB by depolarization is disabled, presumably as part of a cellular commitment to apoptosis.

Antifungal activity in Saccharomyces cerevisiae is modulated by calcium signalling

The most important group of antifungals is the azoles (e.g. miconazole), which act by inhibiting lanosterol demethylase in the sterol biosynthesis pathway. Azole activity can be modulated through structural changes in lanosterol demethylase, altered expression of its gene ERG11, alterations in other sterol biosynthesis enzymes or altered expression of multidrug transporters. We present evidence that azole activity versus Saccharomyces cerevisiae is also modulated by Ca2+-regulated signalling. (i) Azole activity was reduced by the addition of Ca2+. Conversely, azole activity was enhanced by the addition of Ca2+ chelator EGTA. (ii) Three structurally distinct inhibitors (fluphenazine, calmidazolium and a W-7 analogue) of the Ca2+-binding regulatory protein calmodulin enhanced azole activity. (iii) Two structurally distinct inhibitors (cyclosporin and FK506) of the Ca2+-calmodulin-regulated phosphatase calcineurin enhanced azole activity. (iv) Strains in which the Ca2+ binding sites of calmodulin were eliminated and strains in which the calcineurin subunit genes were disrupted demonstrated enhanced azole sensitivity; conversely, a mutant with constitutively activated calcineurin phosphatase demonstrated decreased azole sensitivity. (v) CRZ1/TCN1 encodes a transcription factor regulated by calcineurin phosphatase; its disruption enhanced azole sensitivity, whereas its overexpression decreased azole sensitivity. All the above treatments had comparable effects on the activity of terbinafine, an inhibitor of squalene epoxidase within the sterol biosynthesis pathway, but had little or no effect on the activity of drugs with unrelated targets. (vi) Treatment of S. cerevisiae with azole or terbinafine resulted in transcriptional upregulation of genes FKS2 and PMR1 known to be Ca2+ regulated. A model to explain the role of Ca2+-regulated signalling in azole/terbinafine tolerance is proposed.

Effect of calmidazolium analogs on calcium influx in HL-60 cells

The structure-activity relationships of calmidazolium analogs with respect to intracellular calcium levels were investigated in HL-60 cells. Quaternized derivatives of miconazole and clotrimazole, known inhibitors of store-operated calcium (SOC) channels, were synthesized. The quaternary N-methyl derivatives of miconazole (3) and clotrimazole (6) had no effect on intracellular calcium levels, alone or after elevation of calcium induced by ATP. Calmidazolium alone induced a large increase in intracellular calcium levels in HL-60 cells (EC(50) 3 microM). Similar effects were observed for miconazole derivatives 1 (EC(50) 15 microM) and 2 (EC(50) 10 microM), wherein the diphenylmethyl group in calmidazolium was replaced by a 3,5-difluorobenzyl or cyclohexylmethyl group, respectively. The analogous clotrimazole derivatives 4 and 5 had no effect on intracellular calcium levels. The elevation of calcium levels by calmidazolium, 1, and 2 appears to be comprised of a calcium release component from inositol trisphosphate (IP(3))-sensitive stores followed by a large calcium influx component. Calcium influx was greater than that normally observed due to depletion of IP(3)-sensitive calcium stores and activation of SOC channels. In addition, only a small component of the calmidazolium-elicited influx was inhibited by the SOC channel blocker miconazole. Thus, certain quaternized imidazoles substituted with large residues at both nitrogens of the imidazole ring caused both release and influx of calcium, the latter in part through SOC channels but mainly through an undefined cationic channel. Quaternized imidazoles, unlike the parent nonquaternary imidazole miconazole, did not block SOC channels. Inhibitory effects on calmodulin-activated phosphodiesterase did not correlate with effects on calcium release and influx.

Membrane-bound calmodulin in Xenopus laevis oocytes as a novel binding site for melatonin

Melatonin has been suggested as a physiological antagonist of calmodulin. In this work, we have characterized melatonin binding sites in Xenopus laevis oocyte membranes. Binding of [125I]melatonin by X. laevis oocyte membranes fulfills all criteria for binding to a receptor site. Binding was dependent on time, temperature, and membrane concentration and was stable, reversible, saturable, and specific. The binding site was also pharmacologically characterized. Stoichiometric studies showed a high-affinity binding site with a Kd of 1.18 nM. These data are in close agreement with data obtained from kinetic studies (Kd=0.12 nM). In competition studies, we observed a low-affinity binding site (Kd=63.41 microM). Moreover, the binding site was characterized as calmodulin. Thus, binding was dependent on calcium and blocked by anti-CaM antibodies in a concentration-dependent manner. Calmodulin inhibitor chlorpromazine also inhibited binding of the tracer. From these results, it is suggested that membrane-bound calmodulin acts as a melatonin binding site in Xenopus laevis oocytes, where it might couple cellular activities to rhythmic circulating levels of melatonin. This hypothesis correlates with the previous findings describing melatonin as a physiological antagonist of calmodulin.

Effect of fibrin on endothelial cell production of prostacyclin and tissue plasminogen activator

Fibrin formed on endothelial cells has previously been shown to have deleterious effects on the cells. Additionally, substances that cause endothelial cell damage have been reported to induce cultured endothelial cells to synthesize prostacyclin and tissue plasminogen activator (t-PA). The present studies were undertaken to determine whether fibrin formed on cultured human umbilical vein endothelial cells would alter synthesis of prostacyclin and t-PA by the cells. Fibrin was found to increase synthesis of both prostacyclin and t-PA in a dose and time dependent manner. Stimulation of prostacyclin synthesis was completely inhibited by indomethacin; partially inhibited by actinomycin D, cycloheximide, and trifluoperazine; and not affected by cytochalasin D or vinblastine. In contrast, stimulation of t-PA synthesis was completely inhibited by actinomycin D and cycloheximide; partially inhibited by cytochalasin D, vinblastine, and trifluoperazine; and not affected by indomethacin. Fibrin I, formed with Reptilase, caused only slight stimulation of t-PA production, but virtually no stimulation of prostacyclin synthesis. Neither collagen polymerization on the cells nor thrombin added in concentrations that did not induce fibrin polymer formation stimulated production of either substance. Furthermore, soluble fibrin II generated in the presence of the fibrin polymerization inhibitor gly-pro-arg-pro also failed to stimulate either prostacyclin or t-PA production. The presence of platelets in the plasma from which the fibrin was formed did not affect the amount of stimulation of the cells. Fibrin-induced stimulation of endothelial cell production of prostacyclin and t-PA could act to limit vascular occlusion in vivo by inhibiting platelet function and by stimulating fibrinolysis via t-PA.

The hydrolysis of glycerophosphocholine by rat brain microsomes: activation and inhibition

Experiments with glycerophosphocholine phosphodiesterase (GPC diesterase, EC 3.1.4.2.) in rat brain microsomes suggest that, although its activity is inhibited by low concentrations of calmidazolium, its dependence on Ca2+ ions is not modulated by calmodulin. The activity of glycerophosphocholine choline phosphodiesterase (choline phosphohydrolase, EC 3.1.4.38) was much lower than that of the GPC diesterase. A relatively inexpensive method for the preparation of sn-glycero-3-phospho [Me-14C]choline is described.

Properties of the 23,000-Da phosphoproteins in cardiac sarcolemma and sarcoplasmic reticulum

The calmodulin- and cAMP-dependent protein kinase-mediated phosphorylations of isolated sarcolemma and sarcoplasmic reticulum vesicles have been compared. Similarities in the calmodulin-mediated phosphorylation of the sarcolemma and sarcoplasmic reticulum 23,000-Da phosphoproteins included their Mg2+, Na+, Ca2+, and calmodulin sensitivities, as well as the size of their dissociated subunits. In contrast, a number of differences between these phosphoproteins were indicated in their sensitivity to detergents (Triton X-100 and sodium dodecyl sulfate) and calmodulin antagonists (R24571 and trifluoperazine). Furthermore, in contrast to the sarcoplasmic reticulum phosphoprotein, the sarcolemma phosphoprotein could not be affinity labeled with 125I-calmodulin. While these results indicate the probable chemical similarity of the sarcolemma and sarcoplasmic reticulum 23,000-Da phosphoproteins, they also indicate there are differences in the lipid/phosphoprotein interactions in these two membranes.

Slow calcium channel blockers and calmodulin. Effect of felodipine, nifedipine, prenylamine and bepridil on cardiac sarcolemmal calcium pumping ATPase

The effect of four slow Ca2+ channel blockers (felodipine, nifedipine, prenylamine and bepridil) that possess the ability to bind to calmodulin (CaM) section and to inhibit myosin light chain kinase (MLCK) on CaM-regulated Ca2+ pumping ATPase of cardiac sarcolemma (SL) and brain cyclic AMP phosphodiesterase (PDE) was studied. The ability of these drugs to inhibit Ca2+ pumping ATPase correlated with their inhibitory effect on CaM-activated Ca2+-dependent PDE. Nifedipine was unable to inhibit markedly both enzymes. Prenylamine also was a weak inhibitor, which was unexpected because of its CaM binding potency. Felodipine (10-50 microM) and bepridil (50 microM) markedly reduced activities of SL Ca2+ pumping ATPase and PDE. Striking differences were, however, demonstrated when Ca2+ and CaM concentrations, respectively, were increased. Previously it was reported that inhibition of the SL Ca2+ pumping ATPase by the CaM antagonist calmidazolium could be overcome by increasing Ca2+ concentrations (J. M. J. Lamers and J. T. Stinis, Cell Calcium 4, 281-294, 1983). Felodipine (10-50 microM) in the present study, appeared to be equipotent with calmidazolium in reducing Ca2+ pumping ATPase, but increasing Ca2+ up to 12.2 microM could not counteract this effect. Felodipine (2-10 microM) also inhibited brain PDE noncompetitively with respect to CaM contrary to the competitive effectors calmidazolium and bepridil. On the other hand, bepridil (10-20 microM) decreased or increased Ca2+ pumping ATPase activity depending on the Ca2+ concentration (0.29 and 12.2 microM, respectively) used. These findings suggest at least two types of CaM antagonists, which can be discriminated on basis of their inhibition patterns of PDE and heart SL Ca2+ pumping ATPase.

Calmodulin abolishes the changes in Ca2+ binding and transport by heart sarcolemmal membranes of spontaneously hypertensive rats

Both Ca2+ transport and binding properties of heart sarcolemmal membranes are altered in spontaneously hypertensive rats (SHR) when compared to their normotensive controls (WKY). The effects of calmodulin on these two processes were studied at free calcium concentrations presumed to be the physiological levels in the cytosol. At a calcium concentration of 2.10(-8)M, calmodulin did not significantly modify either binding or ATP-dependent accumulation of calcium by membranes of both origins. In contrast, at a free calcium concentration of 4.10(-7)M, calmodulin enhanced the calcium binding to SHR membranes and the ATP-dependent calcium transport by SHR and WKY membranes. Differences in calcium binding and ATP-dependent accumulation between the two substrains were suppressed in presence of calmodulin. These data demonstrate that modifications in calcium handling by SHR cardiac plasma membranes might be due to altered intracellular content or function of calmodulin in SHR.