Block of inactivation-deficient cardiac Na(+) channels by acetyl-KIFMK-amide

The Na(+) channel alpha-subunit contains an IFM motif that is critical for the fast inactivation process. In this study, we sought to determine whether an IFM-containing peptide, acetyl-KIFMK-amide, blocks open cardiac Na(+) channels via the inner cavity. Intracellular acetyl-KIFMK-amide at 2mM elicited a rapid time-dependent block (tau=0.24 ms) of inactivation-deficient human heart Na(+) channels (hNav1.5-L409C/A410W) at +50 mV. In addition, a peptide-induced tail current appeared conspicuously upon repolarization, suggesting that the activation gate cannot close until acetyl-KIFMK-amide is cleared from the open pore. Repetitive pulses (+50 mV for 20 ms at 1Hz) produced a substantial use-dependent block of both peak and tail currents by approximately 65%. A F1760K mutation (hNav1.5-L409C/A410W/F1760K) abolished the use-dependent block by acetyl-KIFMK-amide and hindered the time-dependent block. Competition experiments showed that acetyl-KIFMK-amide antagonized bupivacaine binding. These results are consistent with a model that two acetyl-KIFMK-amide receptors exist in proximity within the Na(+) channel inner cavity.     

Polarized localization of vitamin C transporters, SVCT1 and SVCT2, in epithelial cells

Messenger RNA of homologous sodium-vitamin C cotransporters, SVCT1 and SVCT2, were found in the intestine. Studies using cultured intestinal cells suggested an apical presence of SVCT1 but the function of SVCT2 was unknown. Here, we showed that enterocytes from heterozygous SVCT2-knockout mice had lower sodium-dependent vitamin C accumulation compared to those from the wildtype. Thus, SVCT2 appears to be functional in enterocytes. We then tested whether SVCT2 could have a redundant function as SVCT1 by constructing and expressing EGFP-tagged SVCTs in intestinal Caco-2 and kidney MDCK cells. In confluent epithelial cells, SVCT1 protein expressed predominantly on the apical membrane. SVCT2, in contrast, accumulated at the basolateral surface. Functionally, SVCT1 expression led to more transport activity from the apical membrane, while SVCT2 expression only increased the uptake under the condition when basolateral membrane was exposed. This differential epithelial membrane distribution and function suggests non-redundant functions of these two isoforms.     

Signals of seminal vesicle autoantigen suppresses bovine serum albumin-induced capacitation in mouse sperm

Capacitation is the prerequisite process for sperm to gain the ability for successful fertilization. Unregulated capacitation will cause sperm to undergo a spontaneous acrosome reaction and then fail to fertilize an egg. Seminal plasma is thought to have the ability to suppress sperm capacitation. However, the mechanisms by which seminal proteins suppress capacitation have not been well understood. Recently, we demonstrated that a major seminal vesicle secretory protein, seminal vesicle autoantigen (SVA), is able to suppress bovine serum albumin (BSA)-induced mouse sperm capacitation. To further identify the mechanism of SVA action, we determine the molecular events associated with SVA suppression of BSA's activity. In this communication, we demonstrate that SVA suppresses the BSA-induced increase of intracellular calcium concentration ([Ca2+]i), intracellular pH (pH(i)), the cAMP level, PKA activity, protein tyrosine phosphorylation, and capacitation in mouse sperm. Besides, we also found that the suppression ability of SVA against BSA-induced protein tyrosine phosphorylation and capacitation could be reversed by dbcAMP (a cAMP agonist).     

Serine proteases and cardiac function

The serine proteases of the trypsin superfamily are versatile enzymes involved in a variety of biological processes. In the cardiovascular system, the importance of these enzymes in blood coagulation, platelet activation, fibrinolysis, and thrombosis has been well established. Recent studies have shown that trypin-like serine proteases are also important in maintaining cardiac function and contribute to heart-related disease processes. In this review, we describe the biological function of corin, tissue kallikrein, chymase and urokinase and discuss their roles in cardiovascular diseases such as hypertension, cardiac hypertrophy, heart failure, and aneurysm.     

Mechanism of the maturation process of SARS-CoV 3CL protease

Severe acute respiratory syndrome (SARS) is an emerging infectious disease caused by a novel human coronavirus. Viral maturation requires a main protease (3CL(pro)) to cleave the virus-encoded polyproteins. We report here that the 3CL(pro) containing additional N- and/or C-terminal segments of the polyprotein sequences undergoes autoprocessing and yields the mature protease in vitro. The dimeric three-dimensional structure of the C145A mutant protease shows that the active site of one protomer binds with the C-terminal six amino acids of the protomer from another asymmetric unit, mimicking the product-bound form and suggesting a possible mechanism for maturation. The P1 pocket of the active site binds the Gln side chain specifically, and the P2 and P4 sites are clustered together to accommodate large hydrophobic side chains. The tagged C145A mutant protein served as a substrate for the wild-type protease, and the N terminus was first digested (55-fold faster) at the Gln(-1)-Ser1 site followed by the C-terminal cleavage at the Gln306-Gly307 site. Analytical ultracentrifuge of the quaternary structures of the tagged and mature proteases reveals the remarkably tighter dimer formation for the mature enzyme (K(d) = 0.35 nm) than for the mutant (C145A) containing 10 extra N-terminal (K(d) = 17.2 nM) or C-terminal amino acids (K(d) = 5.6 nM). The data indicate that immature 3CL(pro) can form dimer enabling it to undergo autoprocessing to yield the mature enzyme, which further serves as a seed for facilitated maturation. Taken together, this study provides insights into the maturation process of the SARS 3CL(pro) from the polyprotein and design of new structure-based inhibitors.     

Anti-inflammatory and neuroprotective effects of magnolol in chemical hypoxia in rat cultured cortical cells in hypoglycemic media

Our previous studies demonstrated that magnolol protects neurons against chemical hypoxia by KCN in cortical neuron-astrocyte mixed cultures (14). In the present study, we examined whether the neuroprotective effect of magnolol involve modulating inflammatory mediators, prostaglandin E2 (PGE2) and nitric oxide (NO), induced by KCN (hypoxia) or KCN plus lipopolysaccharide (LPS). In glucose-absent (hypoglycemia) media, KCN or KCN plus LPS induced increases in lactate dehydrogenase (LDH) activity by 32% and 34%, and PGE2 production by 12% and 32%, respectively. Both LDH and PGE2 increases were suppressed by 100 microM magnolol. In addition, although KCN or LPS alone did not increase NO generation, KCN plus LPS increased NO generation. This increase was reduced by 100 microM magnolol or 10 microM L-NAME, but the LDH increase and PGE2 production were not reduced by L-NAME. These findings suggest that the protective effects of magnolol against brain damage by KCN or KCN plus LPS in hypoglycemic media may involve inhibition of PGE2 production, but inhibition of NO generation may not be important.     

Synthesis of 60- and 72 kDa heat shock proteins in early porcine embryogenesis

Proteins of selected embryonic stages were metabolically labeled with [(35)S]-methionine and analyzed by two-dimensional SDS-polyacrylamide gel electrophoresis (2-D PAGE) to study protein expression from 4- to 8-cell to blastocyst stage of porcine embryos. Two proteins with molecular weights of 60 and 72kDa were de novo synthesized during the 4- to 8-cell stage were the earliest that were detected. They were identified as HSP60 and HSP72 according to their locations on 2-D autoradiography and the immunoblotting result of anti-HSP 60 and HSP 72 antibodies of 1-cell stage of porcine embryos. In protein translation in early pig embryogenesis the timing of their synthesis suggests that HSP60 and HSP72 play significant roles as chaperones.     

Association of heat shock protein 70 with semen quality in boars

This study attempted to clarify the relationship between the levels of 70kDa heat shock protein (HSP70) and semen quality in boars. Semen samples from 29 (13 Duroc, 9 Landrace, and 7 Yorkshire) boars (mean age=25.2+/-2.2 months) were examined. Three to four ejaculates per boar, collected during cool and hot seasons, were evaluated in terms of the sperm concentration, sperm motility, percentage of normal and abnormal sperm, as well as percentage of sperm with proximal and distal plasma droplets. Significant seasonal and breed differences in semen quality were observed. Experimental results indicate that the semen quality of Landrace boars was better than those of Yorkshire and Duroc boars (P<0.05) and semen quality declined significantly during the hot season (P<0.05). One-dimensional SDS-PAGE analysis of spermatozoa proteins indicated that protein profiles did not significantly differ between seasons and among breeds. Both constitutive and stress-inducible form of HSP70 were detected in boar spermatozoa by Western blot analysis. The level of HSP70, which revealed no difference among breeds within a season, was significantly lower during the hot season in all the three breeds (P<0.05). Although there appeared to be low correlation coefficients between the level of HSP70 and semen quality traits, the semen quality tended to decline significantly in samples with a lower level of HSP70. Results in this study suggest that the levels of HSP70 in boar spermatozoa are significantly lower during the hot season and might be associated with semen quality.     

The mechanics of F-actin microenvironments depend on the chemistry of probing surfaces

To understand the microscopic mechanical properties of actin networks, we monitor the motion of embedded particles with controlled surface properties. The highly resolved Brownian motions of these particles reveal the viscoelastic character of the microenvironments around them. In both non-cross-linked and highly cross-linked actin networks, particles that bind F-actin report viscoelastic moduli comparable to those determined by macroscopic rheology experiments. By contrast, particles modified to prevent actin binding have weak microenvironments that are surprisingly insensitive to the introduction of filament cross-links. Even when adjacent in the same cross-linked gel, actin-binding and nonbinding particles report viscoelastic moduli that differ by two orders of magnitude at low frequencies (0.5-1.5 rad/s) but converge at high frequencies (> 10(4) rad/s). For all particle chemistries, electron and light microscopies show no F-actin recruitment or depletion, so F-actin microheterogeneities cannot explain the deep penetration (approximately 100 nm) of nonbinding particles. Instead, we hypothesize that a local depletion of cross-linking around nonbinding particles explains the phenomena. With implications for organelle mobility in cells, our results show that actin binding is required for microenvironments to reflect macroscopic properties, and conversely, releasing actin enhances particle mobility beyond the effects of mere biochemical untethering.     

Erythrocytes possess an intrinsic barrier to nitric oxide consumption

It has been reported that free hemoglobin (Hb) reacts with NO at an extremely high rate (K(Hb) approximately 10(7) M(-1) s(-1)) and that the red blood cell (RBC) membrane is highly permeable to NO. RBCs, however, react with NO 500-1000 times slower. This reduction of NO reaction rate by RBCs has been attributed to the extracellular diffusion limitation. To test whether additional limitations are also important, we designed a competition test, which allows the extracellular diffusion limitation to be distinguished from transmembrane or intracellular resistance. This test exploited the competition between free Hb and RBCs for NO generated in a homogenous phase by an NO donor. If the extracellular diffusion resistance is negligible, then the results would follow a kinetic model that assumes homogenous reaction without extracellular diffusion limitation. In this case, the measured effective reaction rate constant, K(RBC), would remain invariant of the hematocrit, extracellular-free Hb concentration, and NO donor concentration. Results show that the K(RBC) approaches a constant only when the hematocrit is greater than 10%, suggesting that at higher hematocrit, the extracellular diffusion resistance is negligible. Under such a condition, the NO consumption by RBCs is still 500-1000 times slower than that by free Hb. This result suggests that intrinsic RBC factors, such as transmembrane diffusion limitation or intracellular mechanisms, exist to reduce the NO consumption by RBCs.