Backgroundα2-adrenergic receptors (ARs) mediate many cellular actions of epinephrine and norepinephrine and inhibit their secretion from adrenal chromaffin cells. Like many other G-protein coupled receptors (GPCRs), they undergo agonist-dependent phopshorylation and desensitization by GPCR Kinases (GRKs), a phenomenon recently shown to play a major role in the sympathetic overdrive that accompanies and aggravates chronic heart failure. A deletion polymorphism in the human α2B-AR gene (Glu301-303) causes impaired agonist-promoted receptor phosphorylation and desensitization in heterologous cell lines. Given the importance of α2-ARs in regulation of catecholamine secretion from chromaffin cells, we sought to investigate, in the present study, the desensitization properties and the sympatho-inhibitory activity of this variant in a chromaffin cell line. For this purpose, we expressed this variant and its wild type counterpart in the well-established chromaffin cell line PC12, and performed receptor phosphorylation and desensitization studies, as well as in vitro catecholamine secretion assays.ResultsBoth the agonist-induced phosphorylation and agonist-dependent desensitization of the human Glu301-303 deletion polymorphic α2B-AR are significantly impaired in PC12 cells, resulting in enhanced signaling to inhibition of cholinergic-induced catecholamine secretion in vitro.ConclusionThis α2B-AR gene polymorphism (Glu301-303 deletion) might confer better protection against conditions characterized and aggravated by sympathetic/catecholaminergic overstimulation in vivo.

We have examined the differences in urinary excretion of water, sodium, potassium, chloride, urea, and creatinine produced by different dosage regimens offurosemide in normal volunteers. Three oral dosage regimens were compared: 20 mg daily, 20 mg twice daily, and 40 mg daily. Furosemide, 20 mg, did not produce a significant weight loss, diuresis, or natriuresis in 12 normal subjects. With 40 there was a significant weight loss, diuresis, natriuresis, and chloruresis over 24 hr. Comparison of the divided regimen with 40 mg daily revealed significantly greater sodium excretion, and chloride excretion with 20 mg twice daily. The divided dosage regimen produced a different pattern of diuresis with most of the sodium and water excretion occurring after the second dose. These differences in response to different regimens are predictable from pharmacokinetic considerations and may have clinical significance.

No abstract

Tears contain ~60 different proteins that adhere to contact lenses, causing lens deterioration and ocular pathology. We examined the adhesion of three tear proteins to two different types of FDA Group II contact lenses (hilafilcon and omafilcon). Lenses were incubated in 2.0 mg/ml solutions of human lysozyme, albumin and transferrin for 1–4 days. Protein adhesion was determined by bicinchoninic acid assay. Lysozyme adhered to hilafilcon lenses in an up‐down pattern, with a maximum on day 3. Lysozyme adhesion to omafilcon lenses was high after 1 day and remained high on day 4. Albumin adesion to both types of lenses was high after 1 day, declined, and increased on day 4. Transferrin adhesion to both lenses was initally low, increasing to a maximum on day 3 and declining on day 4. These results are due to differences in lens material and tear protein structure. Hilafilcon, more negatively charged than Omafilcon, absorbed more lysozyme (+ charged at physiological pH). Omafilcon lenses are coated with phosphorylcholine, reducing adhesion by the hydrophobic domains of albumin. Human apo‐transferrin has few positive charges and thus bound more reluctantly to both materials.Supported by the Farquhar College of Arts and Sciences and the Health Professions Division, NSU.

Mechanosensitive channels from MscS and MscL families are major components of the tension-driven osmolyte efflux system regulating turgor pressure under day-to-day conditions and rescuing bacteria from rupture under abrupt osmotic down shock. MscL, which opens at higher tension, is considered to be an emergency valve acting at tensions approaching the lytic threshold. In patches taken from WT E. coli or Vibrio cholerae (Vc) spheroplasts, MscL is typically found in higher copy number than MscS, suggesting that the larger channel is the major pathway for expedient release of a larger spectrum of osmolytes in events of near-lethal shock. The smaller MscS was thought to regulate tension at moderate shocks and/or assist in termination of the osmotic permeability response due to its unique ability to inactivate. In this work we prepare the MscL KO construct containing the Kanamycin resistance cassette and 1 kb flanks and utilize the MuGENT technique to induce competence in Vibrio in order to introduce constructs into cells. Screening of 32 resistant candidates revealed a KO clone where the mscL ORF was undetectable. Surprisingly, osmotic shock viability of the KO clone was considerably higher than in WT and the rate of osmolyte release during osmotic shock measured with a millisecond resolution in light scattering stopped-flow experiments was also higher. Preliminary patch-clamp experiments indicated that MscL activities are not found in the KO, but the abundance of MscS increased more than two-fold. The data indicate a strong compensatory reaction in Vc which responds to the absence of MscL with overexpression of the remaining MS channel. The work suggests the presence of physical mechanism allowing bacteria to detect the absence of MscL and trigger a compensatory reaction.