The intrinsic pKa values of the phosphate groups of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) and of the phosphate and carboxyl groups of phosphatidylserine (PS) in self-organized monolayers deposited on a hanging mercury drop electrode were determined by a novel procedure based on measurements of the differential capacity C of this lipid-coated electrode. In view of the Gouy-Chapman theory, plots of 1/C at constant bulk pH and variable KCl concentration against the reciprocal of the calculated diffuse-layer capacity Cd,0 at zero charge exhibit slopes that decrease from an almost unit value to vanishingly low values as the absolute value of the charge density on the lipid increases from zero to approximately 2 microC cm-2. The intrinsic pKa values so determined are 0.5 for PE and 0.8 for PC. The plots of 1/C against 1/Cd,0 for pure PS exhibit slopes that pass from zero to a maximum value and then back to zero as pH is varied from 7.5 to 3, indicating that the charge density of the lipid film passes from slight negative to slight positive values over this pH range. An explanation for this anomalous behavior, which is ascribed to the phosphate group of PS, is provided. Interdispersion of PS and PC molecules in the film decreases the "formal" pKa value of the latter group by about three orders of magnitude.

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SERCA (sarco(endo)plasmic reticulum Ca 2ϩ -ATPase) is a well characterized cation transport ATPase (1-6) that is obtained with vesicular fragments of sarcoplasmic reticulum (SR).2 Two Ca 2ϩ are transported from the medium into the vesicles, whereas one ATP is utilized. ATPase activation requires binding of two Ca 2ϩ per enzyme molecule (E 1 ⅐2Ca 2ϩ ) followed by ATP utilization and formation of a phosphoenzyme intermediate (E 1 -P). The free energy derived from ATP is utilized by the phosphoenzyme for a conformational transition (E 1 -P to E 2 -P) that favors translocation and release of the bound Ca 2ϩ against its concentration gradient. The cycle is completed by hydrolytic cleavage of E 2 -P. Ca 2ϩ /H ϩ countertransport and electrogenicity were noted (7-9) with native SR vesicles, but most useful information was obtained with reconstituted proteoliposomes (10, 11) that are not leaky to H ϩ or other electrolytes. It was then possible to demonstrate that, at neutral pH, the stoichiometry of Ca 2ϩ

A biomimetic membrane consisting of a lipid bilayer tethered to a mercury electrode via a hydrophilic spacer was investigated in aqueous KCl by potential-step chronocoulometry and electrochemical impedance spectroscopy, both in the absence and in the presence of the ionophore valinomycin. Impedance spectra, recorded from 1 x 10(-2) to 1 x 10(5) Hz over a potential range of 0.8 V, are satisfactorily fitted to a series of four RC meshes, which are straightforwardly related to the different substructural elements of the biomimetic membrane. The frequency-independent resistances and conductances of both the lipid bilayer and the hydrophilic spacer show a maximum when plotted against the applied potential. This behavior is interpreted on the basis of a general approximate approach that applies the concepts of impedance spectroscopy to a model of the electrified interphase and to the kinetics of potassium ion transport assisted by valinomycin across the lipid bilayer.

While feverfew has been used for centuries to treat pain and headaches and is recommended for migraine treatment, the mechanism for its protective action remains unknown. Migraine is triggered by calcitonin gene-related peptide (CGRP) release from trigeminal neurons. Peptidergic sensory neurons, express a series of transient receptor potential (TRP) channels, including the ankyrin 1 (TRPA1) channel. Recent findings have identified agents either inhaled from the environment or produced endogenously, which are known to trigger migraine or cluster headache attacks, as TRPA1 simulants. A major constituent of feverfew, parthenolide, may interact with TRPA1 nucleophilic sites, suggesting that feverfew antimigraine effect derives from its ability to target TRPA1. We found that parthenolide stimulates recombinant (transfected cells) or natively expressed (rat/mouse trigeminal neurons) TRPA1, where it, however, behaves as a partial agonist. Furthermore, in rodents, after initial stimulation, parthenolide desensitizes the TRPA1 channel, and renders peptidergic, TRPA1-expressing nerve terminals unresponsive to any stimulus. This effect of parthenolide abrogates nociceptive responses evoked by stimulation of peripheral trigeminal endings. TRPA1 targeting and neuronal desensitization by parthenolide inhibits CGRP release from trigeminal neurons and CGRP-mediated meningeal vasodilatation, evoked by either TRPA1 agonists or other unspecific stimuli. TRPA1 partial agonism, together with desensitization and nociceptor defunctionalization, ultimately resulting in inhibition of CGRP release within the trigeminovascular system, may contribute to the antimigraine effect of parthenolide.