Assay of brain calmodulin levels using high-performance liquid chromatography

Changes in hypothalamic calmodulin concentration induced by perinatal hormone manipulation in the rat

Calmodulin (CaM) presence and concentration was determined (RIA) in the rat hypothalamus (2, 6, 12, 24 h and 90 days after birth) in vehicle-treated animal (controls), in testosterone propionate (TP)-treated females (30 microg/rat subcutaneously 1 h after birth) and in tamoxifen-treated males (200 microg/rat subcutaneously 1 h after birth). CaM concentration, either as total content/hypothalamus or as concentration per mg ww, was significantly higher in both male and female adult rats than in newborn subjects. CaM concentration/mg protein increased with age, being two times higher in adult males and greater than three times higher in adult females than in their respective newborns. Two, 12, and 24 h after birth CaM concentration was significantly lower in control females than in control males. This relation was reversed in adults in which CaM concentration was higher in females. The application of TP to the females and tamoxifen to the males, induced a significant decrease in CaM/mg protein, both in the newborn (2 and 6 h) and in the adult animals. In adults, treated females had CaM concentrations similar to those found in control males. Our data suggest: first, a lasting effect of newborn hormonal treatment upon the CaM concentration in rat hypothalamus; second, that CaM is preferentially synthesized in the adult female hypothalamus, indicating an important role of this protein in female reproductive function.

A quantitative study of the Ca2+/calmodulin sensitivity of adenylyl cyclase in Aplysia, Drosophila, and rat

Studies in Aplysia and Drosophila have suggested that Ca2+/calmodulin-sensitive adenylyl cyclase may act as a site of convergence for the cellular representations of the conditioned stimulus (Ca2+ influx) and unconditioned stimulus (facilitatory transmitter) during elementary associative learning. This hypothesis predicts that the rise in intracellular free Ca2+ concentration produced by spike activity during the conditioned stimulus will cause an increase in the activity of adenylyl cyclase. However, published values for the Ca2+ sensitivity of Ca2+/calmodulin-sensitive adenylyl cyclase in mammals and in Drosophila vary widely. The difficulty in evaluating whether adenylyl cyclase would be activated by physiological elevations in intracellular Ca2+ levels is in part a consequence of the use of Ca2+/EGTA buffers, which are prone to several types of errors. Using a procedure that minimizes these errors, we have quantified the Ca2+ sensitivity of adenylyl cyclase in membranes from Aplysia, Drosophila, and rat brain with purified species-specific calmodulins. In all three species, adenylyl cyclase was activated by an increase in free Ca2+ concentration in the range caused by spike activity. Ca2+ sensitivity was dependent on both calmodulin concentration and Mg2+ concentration. Mg2+ raised the threshold for adenylyl cyclase activation by Ca2+ but also acted synergistically with Ca2+ to activate maximally adenylyl cyclase.

Simple immunoassays for semiquantitative determination of calmodulin (CaM) and anti-CaM. Applications to affinity column chromatography of anti-CaM antibodies and estimation of CaM in synaptosomal membranes from rat cerebral cortex

Dot-immunobinding assay for anti-calmodulin (CaM), and immunoblot assay for CaM have become feasible by proper choice of a fixative, i.e., formaldehyde vapor. The protocol for these simple and convenient immunological procedures is presented. Dot-immunobinding assay could be accomplished in 3 h, and immunoblot assay in 8 h. Activities of anti-CaM antibodies in fractions eluted from CaM affinity column were monitored by immunobinding assay. Semiquantitative immunoblot analysis was used to estimate CaM present in various fractions during preparation of EGTA-washed lysed synaptosomal membranes from rat cerebral cortex. CaM content in the final preparation was estimated at lower than 3 micrograms/mg of membrane protein.

Neurochemical characteristics of a postsynaptic density fraction isolated from adult canine hippocampus

Postsynaptic density and synaptic membrane fractions isolated from hippocampal tissue have been compared to those previously isolated from cerebellum and cerebral cortex. In all respects examined, the isolated hippocampal preparations are similar to the cerebral cortex fractions. The morphology of the postsynaptic density (PSD) preparation is the same and the protein composition is similar, but with higher concentrations of the 51-kDa major protein and of calmodulin, and lower concentrations of actin, in the hippocampal PSD fraction. The binding characteristics for glutamate and GABA are also similar between the two fractions, but with higher Bmax and KD glutamate values and lower Bmax and higher KD GABA values for the hippocampal PSD preparation. Both preparations contain GABAA and GABAB receptors. The PSD fraction contains, as does the cerebral cortex fraction, a calmodulin-dependent binding of the Ca2+ channel antagonist, nitrendipine, as well as a cAMP-dependent and a Ca2+/calmodulin-dependent protein kinase, with the same respective substrates. The value of the hippocampal fractions for studies on long-term potentiation and on kindling in the hippocampus is discussed.

High performance liquid chromatographic properties of peptides and proteins on a dihydroxyalkyl bonded silica stationary phase

The chromatographic behavior of biologically relevant peptides and proteins in the molecular weight range between 200 and 200,000 dalton units were studied on a size exclusion matrix column consisting of an aqueous compatible dihydroxyalkyl bonded silica support. The mechanism of separation appears to be dependent on hydrodynamic radius, hydrophobic and ionic interactions. Support for this contention is based on the chromatographic properties of these peptides and proteins at different mobile phase ionic strengths and pH, oxidation state of amino acid residues and total hydrophobicity of the peptide or protein. This column is also capable of separating native angiotensin-I from its iodinated congener. Recoveries of proteins and peptides from this column ranged between 70-100%. Unlike typical reverse phase separations, this modified silica chromatographic media allows for an alternative technique employing aqueous eluents for rapid separation/isolation and purification of peptides and proteins from natural or synthetic sources.

Determination of calmodulin by competitive binding assay

Calmodulin levels in tissue or cellular extracts can be determined by competition with 125I-calmodulin in a filtration-based direct binding assay. The method is rapid, uses readily available stable components, and possesses a selectivity and sensitivity comparable to that observed with immunoassay and phosphodiesterase activation. This assay provides a tool to readily probe changes in calmodulin levels in cells and tissues as a function of pathophysiologic state.