Molecular Cloning and Characterization of Ribosomal Protein RPS9 in Echinococcus granulosus

Ribosomal protein S9 (RPS9) is an essential functional gene that participates in DNA repair and developmental regulations. A sequence homolog of RPS9 has been found to be upregulated in the protoscoleces (PSCs) of Echinococcus granulosus treated with artemisinin. However, E. granulosus RPS9 (EgRPS9) has not been identified before. In the present study, the 657-base pair (bp) cDNA encoding EgRPS9 was cloned. Amino acid sequence analysis showed that EgRPS9 was similar to the RSP9 proteins from Schistosoma japonicum (SjRPS9, 86%) and Schistosoma mansoni (SmRPS9, 79%). Phylogenetic tree analysis showed that EgRPS9, SmRPS9, and SjRPS9 were clustered together. We detected the EgRPS9 gene and protein expression in PSCs exposed to artesunate (AS) which displayed a dose-dependent reduction in PSC viability for 24 hr. The results showed that the EgRPS9 ratio of the 10-μM AS-treated ( P < 0.01) and 40-μM AS-treated ( P < 0.05) groups were increased from that of the control group. In addition, the level of reactive oxygen species (ROS) in the AS-treated groups increased in a dose-dependent manner compared to the level in the control group. In conclusion, the expression of EgRPS9 could be induced by ROS and might participate in the oxidative damage-based anti-parasite mechanism of AS treatment.

Long-term blood glucose monitoring with implanted telemetry device in conscious and stress-free cynomolgus monkeys

AIMS

Continuous blood glucose monitoring, especially long-term and remote, in diabetic patients or research is very challenging. Nonhuman primate (NHP) is an excellent model for metabolic research, because NHPs can naturally develop Type 2 diabetes mellitus (T2DM) similarly to humans. This study was to investigate blood glucose changes in conscious, moving-free cynomolgus monkeys (Macaca fascicularis) during circadian, meal, stress and drug exposure.

MATERIALS AND METHODS

Blood glucose, body temperature and physical activities were continuously and simultaneously recorded by implanted HD-XG telemetry device for up to 10 weeks.

RESULTS AND DISCUSSION

Blood glucose circadian changes in normoglycemic monkeys significantly differed from that in diabetic animals. Postprandial glucose increase was more obvious after afternoon feeding. Moving a monkey from its housing cage to monkey chair increased blood glucose by 30% in both normoglycemic and diabetic monkeys. Such increase in blood glucose declined to the pre-procedure level in 30 min in normoglycemic animals and >2 h in diabetic monkeys. Oral gavage procedure alone caused hyperglycemia in both normoglycemic and diabetic monkeys. Intravenous injection with the stress hormones, angiotensin II (2 μg/kg) or norepinephrine (0.4 μg/kg), also increased blood glucose level by 30%. The glucose levels measured by the telemetry system correlated significantly well with glucometer readings during glucose tolerance tests (ivGTT or oGTT), insulin tolerance test (ITT), graded glucose infusion (GGI) and clamp.

CONCLUSION

Our data demonstrate that the real-time telemetry method is reliable for monitoring blood glucose remotely and continuously in conscious, stress-free, and moving-free NHPs with the advantages highly valuable to diabetes research and drug discovery.

Identification of the CAD gene from Eucalyptus urophylla GLU4 and its functional analysis in transgenic tobacco

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the final step in lignin biosynthesis. The genus Eucalyptus belongs to the family Myrtaceae, which is the main cultivated species in China. Eucalyptus urophylla GLU4 (GLU4) is widely grown in Guangxi. It is preferred for pulping because of its excellent cellulose content and fiber length. Based on GLU4 and CAD gene expression, a Eucalyptus variety low in lignin content should be obtained using transgenic technology, which could reduce the cost of pulp and improve the pulping rate, and have favorable prospects for application. However, the role and function of CAD in GLU4 is still unclear. In the present study, EuCAD was cloned from GLU4 and identified using bioinformatic tools. Subsequently, in order to evaluate its impact on lignin synthesis, a full-length EuCAD RNAi vector was constructed, and transgenic tobacco was obtained via Agrobacterium-mediated transformation. A significant decrease in CAD expression and lignin content in transgenic tobacco demonstrated a key role for EuCAD in lignin biosynthesis and established a regulatory role for RNAi. In our study, the direct molecular basis of EuCAD expression was determined, and the potential regulatory effects of this RNAi vector on lignin biosynthesis in E. urophylla GLU4 were demonstrated. Our results provide a theoretical basis for the study of lignin biosynthesis in Eucalyptus.

Association study between matrix metalloproteinase-9 gene (MMP9) polymorphisms and the risk of Henoch-Schönlein purpura in children

Henoch-Schönlein purpura nephritis (HSPN), the most serious long-term complication of Henoch-Schönlein purpura, is one of the most common renal diseases in children. Matrix metalloproteinase-9 (MMP-9) is implicated in the pathogenesis of renal diseases. Genomic DNA was isolated from the venous blood leukocytes of 220 unrelated patients with HSPN and 205 unrelated healthy individuals. To identify markers contributing to genetic susceptibility to HSPN, this study examined the potential association between HSPN and four single nucleotide polymorphisms of the MMP-9 gene (MMP9) (rs17576, rs3918254, rs3787268, and rs2236416) by using the MassARRAY system. The allelic or genotypic frequencies of the rs17576 (exon 6) and rs3918254 (intron 6) polymorphisms in HSPN were significantly different from those in the healthy controls. The HSPN subjects had a significantly higher frequency of the G allele of rs17576 (χ(2) = 8.416, P = 0.004, OR = 1.556, 95%CI = 1.153-2.100) and a significantly lower frequency of the A allele of rs2236416 (χ(2) = 10.363, P = 0.001, OR = 0.545, 95%CI = 0.375-0.791). Linkage disequilibrium was observed in two blocks (D' > 0.9; r(2) > 0.8 in control). In block 1, significantly more G-C haplotypes (P = 0.011) and significantly fewer A-C haplotypes (P = 0.008) were found in the HSPN subjects. In block 2, significantly more G-G haplotypes (P = 0.016) and significantly fewer A-G haplotypes (P = 0.006) were found in the HSPN subjects. These observations suggest that the rs17576 and rs3918254 polymorphisms of MMP9 are associated with HSPN.

Ecdysone receptor isoform-B mediates soluble trehalase expression to regulate growth and development in the mirid bug, Apolygus lucorum (Meyer-Dür)

Ecdysone receptor (EcR) is the hormonal receptor of ecdysteroids and strictly regulates growth and development in insects. However, the action mechanism of EcR is not very clear. In this study, the cDNA of EcR isoform-B was cloned from Apolygus lucorum (AlEcR-B) and its expression profile was investigated. We reduced AlEcR-B mRNA expression using systemic RNA interference in vivo, and obtained knockdown specimens. Examination of these specimens indicated that AlEcR-B is required for nymphal survival, and that reduced expression is associated with longer development time and lower nymphal weight. To investigate the underlying molecular mechanism of the observed suppression effects, we selected trehalase for a detailed study. Transcript encoding soluble trehalase (AlTre-1) was up-regulated by 20-hydroxyecdysone and in agreement with the mRNA expression of AlEcR-B. The expression profile of AlTre-1, soluble trehalase activity and translated protein level in the midgut of surviving nymphs were down-regulated, compared with controls, after the knockdown expression of AlEcR-B. By contrast, membrane-bound trehalase activity, the related gene expression and translated protein level remained at their initial levels. However, trehalose content significantly increased and the glucose content significantly decreased under the same conditions. We propose that AlEcR-B controls normal carbohydrate metabolism by mediating the expression of AlTre-1 to regulate the growth and development in A. lucorum, which provide an extended information into the functions of AlEcR-B.

Late Permian marine ecosystem collapse began in deeper waters: evidence from brachiopod diversity and body size changes

Analysis of Permian-Triassic brachiopod diversity and body size changes from different water depths spanning the continental shelf to basinal facies in South China provides insights into the process of environmental deterioration. Comparison of the temporal changes of brachiopod diversity between deepwater and shallow-water facies demonstrates that deepwater brachiopods disappeared earlier than shallow-water brachiopods. This indicates that high environmental stress commenced first in deepwater settings and later extended to shallow waters. This environmental stress is attributed to major volcanic eruptions, which first led to formation of a stratified ocean and a chemocline in the outer shelf and deeper water environments, causing the disappearance of deep marine benthos including brachiopods. The chemocline then rapidly migrated upward and extended to shallow waters, causing widespread mass extinction of shallow marine benthos. We predict that the spatial and temporal patterns of earlier onset of disappearance/extinction and ecological crisis in deeper water ecosystems will be recorded during other episodes of rapid global warming.

Genetic diversity and relationships in cultivars of Lolium multiflorum Lam. using sequence-related amplified polymorphism markers

Sequence-related amplified polymorphism (SRAP) markers were used to analyze and estimate the genetic variability, level of diversity, and relationships among 20 cultivars and strains of annual ryegrass (Lolium multiflorum Lam.). Eighteen SRAP primer combinations generated 334 amplification bands, of which 298 were polymorphic. The polymorphism information content ranged from 0.4715 (me10 + em1) to 0.5000 (me5 + em7), with an average of 0.4921. The genetic similarity coefficient ranged from 0.4304 to 0.8529, and coefficients between 0.65 and 0.90 accounted for 90.00%. The cluster analysis separated the accessions into five groups partly according to their germplasm resource origins.

Saturation of the photoluminescence at few-exciton levels in a single-walled carbon nanotube under ultrafast excitation

Single air-suspended carbon nanotubes (length 2-5 microm) exhibit high optical quantum efficiency (7-20%) for low intensity resonant pumping. Under ultrafast excitation (150 fs), emission dramatically saturates at very low exciton numbers (2-6), which is attributed to highly efficient exciton-exciton annihilation over micron-length scales. Similar saturation behavior for 4 ps pulse excitation shows nonlinear absorption is not a contributing factor. The absorption cross sections (0.6-1.8x10(-17) cm2/atom) are determined by fitting to a stochastic model for exciton dynamics.

Low-threshold microlaser in a high-Q asymmetrical microcavity

We experimentally report an asymmetrical spherical microcavity with thermal-induced deformation, in which five-bounce whispering-gallery modes possess not only ultrahigh quality factors (Q) but also remarkably directional escape emission from the microsphere boundary. With efficient free-space excitation and collection, a low-threshold microlaser is demonstrated and exhibits a highly directional emission. Our measurement agrees well with the theoretical predictions by corrected Fresnel law.

Membrane Effects of the n-3 Fish Oil Fatty Acids, which Prevent Fatal Ventricular Arrhythmias

Fish oil fatty acids are known to exert beneficial effects on the heart and vascular systems. We have studied the membrane effects on ion channel conductance by the n-3 fish oil fatty acids that account for these beneficial effects. We have confirmed that these fatty acids prevent fatal cardiac arrhythmias in a reliable dog model of sudden cardiac death. This finding was followed by experiments indicating that the n-3 fatty acids electrically stabilize heart cells and do so largely through modulation of the fast voltage-dependent Na(+) currents and the L-type Ca(2+) channels in a manner, which makes the heart cells resistant to arrhythmias. Others and we have demonstrated that these membrane effects on the heart can prevent fatal cardiac arrhythmias in humans.

The Antiarrhythmic Effect of n-3 Polyunsaturated Fatty Acids: Modulation of Cardiac Ion Channels as a Potential Mechanism

Sudden cardiac death remains one of the most serious medical challenges in Western countries. Increasing evidence in recent years has demonstrated that the n-3 polyunsaturated fatty acids (PUFAs) can prevent fatal ventricular arrhythmias in experimental animals and probably in humans. Dietary supplement of fish oils or intravenous infusion of the n-3 PUFAs prevents ventricular fibrillation caused by ischemia/reperfusion. Similar antiarrhythmic effects of these fatty acids are also observed in cultured mammalian cardiomyocytes. Based on clinical observations and experimental studies in vitro and in vivo, several mechanisms have been postulated for the antiarrhythmic effect of the n-3 PUFAs. The data from our laboratory and others have shown that the n-3 PUFAs are able to affect the activities of cardiac ion channels. The modulation of channel activities, especially voltage-gated Na(+) and L-type Ca(2+) channels, by the n-3 fatty acids may explain, at least partially, the antiarrhythmic action. It is not clear, however, whether one or more than one mechanism involves the beneficial effect of the n-3 PUFAs on the heart. This article summarizes our recent studies on the specific effects of the n-3 PUFAs on cardiac ion channels. In addition, the effect of the n-3 PUFAs on the human hyperpolarization-activated cyclic-nucleotide-modulated channel is presented.

Control of laser-beam propagation and absorption in a nanoplasma gas by programming of a transient complex refractive index with a prepulse

By utilizing the intensity- and duration-dependent heating and expansion rate of nanoplasma to generate a transient transverse gradient of the refractive index, prepulse controlled laser-beam propagation is demonstrated. The dynamical response of the macroscopic optical refractive index is traced back to the microscopic polarizability of nanoplasmas experimentally, in accordance with hydrodynamic nanoplasma models. In particular, the delay between the prepulse and the main pulse for maximum Rayleigh scattering is found to be longer than that for maximum x-ray emission, supporting the more refined one-dimensional self-consistent hydrodynamic nanoplasma model.

Interactions of n-3 fatty acids with ion channels in excitable tissues

In summary, we have shown that the conventional explanation for the site of action of a ligand which alters the conductance of a membrane ion channel is that the ligand interacts or binds with the ion channel protein, changing its conductance, is inadequate to explain the primary site of action of the antiarrhythmic n-3 PUFAs. We have shown that when a neutral asparagine is replaced by a positively charged lysine in the N406 amino acid site in the alpha-subunit of the human cardiac sodium channel, the n-3 fatty acids lose their inhibitory action on the sodium current. The inadequacy of this finding to explain the primary site of action of the n-3 PUFAs is demonstrated by the inhibitory effect on all other cardiac ion channels, so far tested. We show that ion channels, which share no amino acid homology with the PUFAs, have their conductance also reduced in the presence of the PUFAs, Thus a more general conceptual framework or paradigm is needed to account for the broad action of the PUFAs on diverse different ion channels lacking amino acid homology. We have been testing the membrane tension hypothesis of Andersen and associates. According to this hypothesis, the fatty acids are not acting directly on the ion channel protein but accumulating in the phospholipid membrane in immediate juxtaposition to the site in the membrane where the ion channel protein penetrates the membrane phospholipid bilayer. This alters membrane tensions exerted by the phospholipid membrane on the ion channel, which in turn causes conformational changes in the ion channel, altering the conductance of the ion channel. Our preliminary data seem to support this membrane tension hypothesis.

Partial correction of defective Cl(-) secretion in cystic fibrosis epithelial cells by an analog of squalamine

Defective cystic fibrosis (CF) transmembrane conductance regulator (CFTR)-mediated Cl(-) transport across the apical membrane of airway epithelial cells is implicated in the pathophysiology of CF lungs. A strategy to compensate for this loss is to augment Cl(-) transport through alternative pathways. We report here that partial correction of this defect could be attained through the incorporation of artificial anion channels into the CF cells. Introduction of GL-172, a synthetic analog of squalamine, into CFT1 cells increased cell membrane halide permeability. Furthermore, when a Cl(-) gradient was generated across polarized monolayers of primary human airway or Fischer rat thyroid cells in an Ussing chamber, addition of GL-172 caused an increase in the equivalent short-circuit current. The magnitude of this change in short-circuit current was ~30% of that attained when CFTR was maximally stimulated with cAMP agonists. Patch-clamp studies showed that addition of GL-172 to CFT1 cells also increased whole cell Cl(-) currents. These currents displayed a linear current-voltage relationship and no time dependence. Additionally, administration of GL-172 to the nasal epithelium of transgenic CF mice induced a hyperpolarization response to perfusion with a low-Cl(-) solution, indicating restoration of Cl(-) secretion. Together, these results demonstrate that in CF airway epithelial cells, administration of GL-172 is capable of partially correcting the defective Cl(-) secretion.

Single point mutations affect fatty acid block of human myocardial sodium channel alpha subunit Na+ channels

Suppression of cardiac voltage-gated Na(+) currents is probably one of the important factors for the cardioprotective effects of the n-3 polyunsaturated fatty acids (PUFAs) against lethal arrhythmias. The alpha subunit of the human cardiac Na(+) channel (hH1(alpha)) and its mutants were expressed in human embryonic kidney (HEK293t) cells. The effects of single amino acid point mutations on fatty acid-induced inhibition of the hH1(alpha) Na(+) current (I(Na)) were assessed. Eicosapentaenoic acid (EPA, C20:5n-3) significantly reduced I(Na) in HEK293t cells expressing the wild type, Y1767K, and F1760K of hH1(alpha) Na(+) channels. The inhibition was voltage and concentration-dependent with a significant hyperpolarizing shift of the steady state of I(Na). In contrast, the mutant N406K was significantly less sensitive to the inhibitory effect of EPA. The values of the shift at 1, 5, and 10 microM EPA were significantly smaller for N406K than for the wild type. Coexpression of the beta(1) subunit and N406K further decreased the inhibitory effects of EPA on I(Na) in HEK293t cells. In addition, EPA produced a smaller hyperpolarizing shift of the V(1/2) of the steady-state inactivation in HEK293t cells coexpressing the beta(1) subunit and N406K. These results demonstrate that substitution of asparagine with lysine at the site of 406 in the domain-1-segment-6 region (D1-S6) significantly decreased the inhibitory effect of PUFAs on I(Na), and coexpression with beta(1) decreased this effect even more. Therefore, asparagine at the 406 site in hH1(alpha) may be important for the inhibition by the PUFAs of cardiac voltage-gated Na(+) currents, which play a significant role in the antiarrhythmic actions of PUFAs.

Point mutations in alpha-subunit of human cardiac Na+ channels alter Na+ current kinetics

Dietary polyunsaturated fatty acids (PUFAs) prevent ischemia-induced fatal cardiac arrhythmias in animals and probably in humans. This action results from inhibition of ion currents for Na+, Ca2+, and possibly other ions. To extend understanding of this protection we are seeking a possible binding site for the PUFAs on the alpha-subunit of the human cardiac Na+ channel, hH1alpha, transiently expressed in HEK293t cells. Three mutated single amino acid substitutions with lysine were made in the alpha-subunit at Domain 4-Segment 6 (D4-S6) for F1760, Y1767 and at D1-S6 for N406. These are in the putative sites of binding of local anesthetics and batrachotoxin, respectively. The mutants F1760K, Y1767K, and N406K, separately and to different extents, affected the current density, the steady-state inactivation potential, accelerated inactivation, delayed recovery from inactivation, and affected voltage-dependent block, but did not affect activation of the hH1alpha. It is essential to learn that single point mutations in D1-S6 and D4-S6 alone significantly modify the kinetics of human cardiac hH1alpha Na+ currents. The effects of PUFAs on these mutant channels will be the subject of subsequent reports.

Mechanism of suppression of cardiac L-type Ca(2+) currents by the phospholipase A(2) inhibitor mepacrine

Phospholipase A(2) plays a crucial role in the release of arachidonic acid (AA) from membrane phospholipids and in myocardial injury during ischemia and reperfusion. Mepacrine, a phospholipase A(2) inhibitor, has been shown to protect the heart from ischemic injury. In order to examine the mechanism of this protection, we investigated the effects of mepacrine on the L-type Ca(2+) current (I(Ca,L)) in rat single ventricular myocytes. Extracellular application of mepacrine significantly inhibited I(Ca,L) in a tonic- and use-dependent manner. The inhibition was also concentration-dependent with an IC(50) of 5.2 microM. Neither the activation nor the steady-state inactivation of I(Ca,L) was altered by mepacrine. The mepacrine-induced inhibition of I(Ca,L) was reversible after washout of the inhibitor. Addition of 1 microM AA partially reversed the mepacrine-induced inhibition of I(Ca,L). Intracellular dialysis, with 2 mM cAMP, significantly increased I(Ca, L), but did not prevent the mepacrine-induced inhibition of I(Ca,L). In addition, extracellular application of isoproterenol or membrane permeable db-cAMP did not reverse the mepacrine-induced inhibition of I(Ca,L). Biochemical measurement revealed that incubation of ventricular myocytes with mepacrine significantly reduced intracellular cAMP levels. The mepacrine-induced reduction of cAMP production was abolished by addition of AA. Our results demonstrate that mepacrine strongly inhibits cardiac I(Ca,L). While mepacrine is a phospholipase A(2) inhibitor and reduces cAMP production, its inhibitory effect on I(Ca,L) mainly results from a direct block of the channel. Therefore, we speculate that the protective effect of mepacrine during myocardial ischemia and reperfusion mostly relates to its blockade of Ca(2+) channels.

cAMP activates an ATP-permeable pathway in neonatal rat cardiac myocytes

The molecular mechanisms associated with intracellular ATP release by the heart are largely unknown. In this study the luciferin-luciferase assay and patch-clamp techniques were used to characterize the pathways responsible for ATP release in neonatal rat cardiac myocytes (NRCM). Spontaneous ATP release by NRCM was significantly increased after cAMP stimulation under physiological conditions. cAMP stimulation also induced an anion-selective electrodiffusional pathway that elicited linear, diphenylamine-2-carboxylate (DPC)-inhibitable Cl(-) currents in either symmetrical MgCl(2) or NaCl. ATP, adenosine 5'-O-(3-thiotriphosphate), and the ATP derivatives ADP and AMP, permeated this pathway; however, GTP did not. The cAMP-induced ATP currents were inhibited by DPC and glibenclamide and by a monoclonal antibody raised against the R domain of the cystic fibrosis transmembrane conductance regulator (CFTR). The channel-like nature of the cAMP-induced ATP-permeable pathway was also determined by assessing protein kinase A-activated single channel Cl(-) and ATP currents in excised inside-out patches of NRCM. Single channel currents were inhibited by DPC and the anti-CFTR R domain antibody. Thus the data in this report demonstrate the presence of a cAMP-inducible electrodiffusional ATP transport mechanism in NRCM. Based on the pharmacology, patch-clamping data, and luminometry studies, the data are most consistent with the role of a functional CFTR as the anion channel implicated in cAMP-activated ATP transport in NRCM.

Coexpression with beta(1)-subunit modifies the kinetics and fatty acid block of hH1(alpha) Na(+) channels

Voltage-gated cardiac Na(+) channels are composed of alpha- and beta(1)-subunits. In this study beta(1)-subunit was cotransfected with the alpha-subunit of the human cardiac Na(+) channel (hH1(alpha)) in human embryonic kidney (HEK293t) cells. The effects of this coexpression on the kinetics and fatty acid-induced suppression of Na(+) currents were assessed. Current density was significantly greater in HEK293t cells coexpressing alpha- and beta(1)-subunits (I(Na,alpha beta)) than in HEK293t cells expressing alpha-subunit alone (I(Na,alpha)). Compared with I(Na,alpha), the voltage-dependent inactivation and activation of I(Na,alpha beta) were significantly shifted in the depolarizing direction. In addition, coexpression with beta(1)-subunit prolonged the duration of recovery from inactivation. Eicosapentaenoic acid [EPA, C20:5(n-3)] significantly reduced I(Na,alpha beta) in a concentration-dependent manner and at 5 microM shifted the midpoint voltage of the steady-state inactivation by -22 +/- 1 mV. EPA also significantly accelerated channel transition from the resting state to the inactivated state and prolonged the recovery time from inactivation. Docosahexaenoic acid [C22:6(n-3)], alpha-linolenic acid [C18:3(n-3)], and conjugated linoleic acid [C18:2(n-6)] at 5 microM significantly inhibited both I(Na,alpha beta) and I(Na,alpha.) In contrast, saturated and monounsaturated fatty acids had no effects on I(Na,alpha beta). This finding differs from the results for I(Na,alpha), which was significantly inhibited by both saturated and unsaturated fatty acids. Our data demonstrate that functional association of beta(1)-subunit with hH1(alpha) modifies the kinetics and fatty acid block of the Na(+) channel.

The antiarrhythmic and anticonvulsant effects of dietary N-3 fatty acids

It has been shown in animals and probably in humans, that n-3 polyunsaturated fatty acids (PUFAs) are antiarrhythmic. We report recent studies on the antiarrhythmic actions of PUFAs. The PUFAs stabilize the electrical activity of isolated cardiac myocytes by modulating sarcolemmal ion channels, so that a stronger electrical stimulus is required to elicit an action potential and the refractory period is markedly prolonged. Inhibition of voltage-dependent sodium currents, which initiate action potentials in excitable tissues, and of the L-type calcium currents, which initiate release of sarcoplasmic calcium stores that increase cytosolic free calcium concentrations and activate the contractile proteins in myocytes, appear at present to be the probable major antiarrhythmic mechanism of the PUFAs.

Experimental studies on antiarrhythmic and antiseizure effects of polyunsaturated fatty acids in excitable tissues

It has been shown that in animals, and probably in humans, n-3 polyunsaturated fatty acids (PUFAs) are antiarrhythmic. We discuss our recent studies on the antiarrhythmic actions of PUFAs. PUFAs stabilize the electrical activity of isolated cardiac myocytes by requiring a stronger electrical stimulus to elicit an action potential and by markedly prolonging the refractory period. These electrophysiologic effects are the result of specific modulation of ion currents, particularly of the voltage-dependent sodium current and of the L-type calcium currents across sarcolemmal phospholipid membranes. This appears to be the probable major antiarrhythmic mechanism of PUFAs. However, they also similarly affect neuronal ion channels with potentially important functional effects on the nervous system.

n-3 fatty acids in the prevention of cardiac arrhythmias

In animals and probably in humans n-3 polyunsaturated fatty acids (PUFA) are antiarrhythmic. A report follows on the recent studies of the antiarrhythmic actions of PUFA. The PUFA stabilize the electrical activity of isolated cardiac myocytes by inhibiting sarcolemmal ion channels, so that a stronger electrical stimulus is required to elicit an action potential and the relative refractory period is markedly prolonged. This appears at present to be the probable major antiarrhythmic mechanism of PUFA.

Functional and electrophysiologic effects of polyunsaturated fatty acids on exictable tissues: heart and brain

It has been shown in animals and probably in humans, that n-3 polyunsaturated fatty acids (PUFAs) are antiarrhythmic. The free PUFAs stabilize the electrical activity of isolated cardiac myocytes by inhibiting sarcolemmal ion channels, so that a stronger electrical stimulus is required to elicit an action potential and the relative refractory period is markedly prolonged. This appears at present to be the probable major antiarrhythmic mechanism of the PUFAs. They similarly inhibit the Na+ and Ca2+ currents in rat hippocampal neurons which results in an increase in the electrical threshold for generalized seizures using the cortical stimulation model in rats.

State-dependent cocaine block of sodium channel isoforms, chimeras, and channels coexpressed with the beta1 subunit

Cocaine block of human cardiac (hH1) and rat skeletal (mu1) muscle sodium channels was examined under whole-cell voltage clamp in transiently transfected HEK293t cells. Low affinity block of resting mu1 and hH1 channels at -180 mV was the same, and high affinity block of inactivated channels at -70 mV was the same. Cocaine block of hH1 channels was greater than block of mu1 channels at voltages between -120 mV and -90 mV, suggesting that greater steady-state inactivation of hH1 channels in this voltage range makes them more susceptible to cocaine block. We induced shifts in the voltage dependence of steady-state inactivation at mu1 and hH1 channels by constructing mu1/hH1 channel chimeras or by coexpressing the wild-type channels with the rat brain beta1 subunit. In contrast to several previous reports, coexpression of the rat brain beta1 subunit with mu1 or hH1 produced large positive shifts in steady-state inactivation. Shifts in the voltage dependence of steady-state inactivation elicited linear shifts in steady-state cocaine block, yet these manipulations did not affect the cocaine affinity of resting or inactivated channels. These data, as well as simulations used to predict block, indicate that state-dependent cocaine block depends on both steady-state inactivation and channel activation, although inactivation appears to have the predominant role.

Cardiac Gsalpha overexpression enhances L-type calcium channels through an adenylyl cyclase independent pathway

The alpha subunit of the stimulatory heterotrimeric G protein (Gsalpha) is critical for the beta-adrenergic receptor activation of the cAMP messenger system. The role of Gsalpha in regulating cardiac Ca2+ channel activity, however, remains controversial. Cultured neonatal cardiac myocytes from transgenic mice overexpressing cardiac Gsalpha were used to assess the role of Gsalpha on the whole-cell Ca2+ currents (ICa). Cardiac myocytes from transgenic mice had a 490% higher peak ICa compared with those of either wild-type controls or Gsalpha-nonexpressing littermates. The effect of Gsalpha overexpression was mimicked by intracellular dialysis of wild-type cardiac myocytes with GTPgammaS-activated Gsalpha. This effect was not mediated by protein kinase A activation as intracellular perfusion with a protein kinase A inhibitor rendered the same degree of activation in either transgenic or wild-type myocytes also dialyzed with activated Gsalpha. The data indicate that Gsalpha overexpression is associated with a constitutive enhancement of ICa which is independent of the cAMP pathway and activation of endogenous adenylyl cyclase.

Partial restoration of cAMP-stimulated CFTR chloride channel activity in DeltaF508 cells by deoxyspergualin

Deletion of the codon encoding phenylalanine 508 (DeltaF508) is the most common mutation in cystic fibrosis (CF) and results in a trafficking defect. Mutant DeltaF508-CF transmembrane conductance regulator (CFTR) protein retains functional activity, but the nascent protein is recognized as abnormal and, in consequence, is retained in the endoplasmic reticulum (ER) and degraded. It has been proposed that this retention in the ER is mediated, at least in part, by the cellular chaperones heat shock protein (HSP) 70 and calnexin. We have investigated the ability of deoxyspergualin (DSG), a compound known to compete effectively for binding with HSP70 and HSP90, to promote trafficking of DeltaF508-CFTR to the cell membrane. We show that DSG treatment of immortalized human CF epithelial cells (DeltaF508) and cells expressing recombinant DeltaF508-CFTR partially restored cAMP-stimulated CFTR Cl- channel activity at the plasma membrane. Although there are several possible explanations for these results, one simple interpretation is that DSG may have altered the interaction between DeltaF508-CFTR and its associated chaperones. If this is correct, agents capable of altering the normal functioning of cellular chaperones may provide yet another means of restoring CFTR Cl- channel activity to CF subjects harboring this class of mutations.

Cytochrome P450: a novel system modulating Ca2+ channels and contraction in mammalian heart cells

1. Cytochrome P450 (P450) is a ubiquitous enzyme system that catalyses oxidative reactions of numerous endogenous and exogenous compounds. The modulatory effects of P450 on the L-type Ca2+ current (ICa), intracellular free Ca2+ signals and cell shortening were assessed in adult rat single ventricular myocytes. 2. Bath administration of the imidazole antimycotics, clotrimazole, econazole and miconazole, which are potent P450 inhibitors, significantly suppressed cardiac ICa. While the Ca2+ channel antagonist nifedipine blocked ICa within 30 s, clotrimazole-induced suppression of ICa required 5.1 +/- 0.4 min (n = 14) to reach a steady low level. The suppression of ICa was dose dependent and recovered after washout of clotrimazole. Intracellular dialysis with the P450 antibody anti-rat CYP1A2 also significantly reduced cardiac ICa. 3. Additional administration of the beta-adrenergic agonist isoprenaline (1 microM) or the membrane-permeable 8-bromo-cAMP (2 mM) completely reversed the suppressant effects of clotrimazole and NaCN on ICa. In addition, intracellular dialysis with 2 mM cAMP abolished the P450 inhibitor-induced suppression of ICa. Phosphorylation of the channel with hydrolysis-resistant ATPgammaS prevented the suppressant effect of clotrimazole on ICa. Furthermore, dephosphorylation of the Ca2+ channel with intracellular dialysis with phosphatase types I and II reduced ICa by 85 +/- 3 % and abolished clotrimazole-induced suppression of ICa. 4. Extracellular administration of the phospholipase A2 inhibitors mepacrine and 4-bromophenacyl bromide significantly suppressed ICa. 5. Clotrimazole, econazole, miconazole and CN- also significantly inhibited intracellular free Ca2+ signals and cell shortening in rat single ventricular myocytes. 6. Intracellular cAMP content was significantly reduced in isolated ventricular myocytes incubated with clotrimazole or CN-. Extracellular administration of 11, 12-epoxyeicosatrienoic acid, one of the P450-mediated metabolites of arachidonic acid, enhanced ICa and intracellular cAMP content. The epoxyeicosatrienoic acid also restored the amplitude of the reduced ICa in P450 antibody-dialysed myocytes. 7. The present data suggest that cytochrome P450 modulates cardiac ICa and cell contraction, and the modulation may result from changes in intracellular levels of cAMP by P450- mediated metabolites of arachidonic acid.

Fatty acids suppress voltage-gated Na+ currents in HEK293t cells transfected with the alpha-subunit of the human cardiac Na+ channel

Studies have shown that fish oils, containing n-3 fatty acids, have protective effects against ischemia-induced, fatal cardiac arrhythmias in animals and perhaps in humans. In this study we used the whole-cell voltage-clamp technique to assess the effects of dietary, free long-chain fatty acids on the Na+ current (INa,alpha) in human embryonic kidney (HEK293t) cells transfected with the alpha-subunit of the human cardiac Na+ channel (hH1alpha). Extracellular application of 0.01 to 30 microM eicosapentaenoic acid (EPA, C20:5n-3) significantly reduced INa,alpha with an IC50 of 0.51 +/- 0.06 microM. The EPA-induced suppression of INa,alpha was concentration- and voltage-dependent. EPA at 5 microM significantly shifted the steady-state inactivation relationship by -27.8 +/- 1.2 mV (n = 6, P < 0.0001) at the V1/2 point. In addition, EPA blocked INa,alpha with a higher "binding affinity" to hH1alpha channels in the inactivated state than in the resting state. The transition from the resting state to the inactivated state was markedly accelerated in the presence of 5 microM EPA. The time for 50% recovery from the inactivation state was significantly slower in the presence of 5 microM EPA, from 2.1 +/- 0.8 ms for control to 34.8 +/- 2.1 ms (n = 5, P < 0.001). The effects of EPA on INa,alpha were reversible. Furthermore, docosahexaenoic acid (C22:6n-3), alpha-linolenic acid (C18:3n-3), conjugated linoleic acid (C18:2n-7), and oleic acid (C18:1n-9) at 5 microM and all-trans-retinoic acid at 10 microM had similar effects on INa,alpha as EPA. Even 5 microM of stearic acid (C18:0) or palmitic acid (C16:0) also significantly inhibited INa, alpha. In contrast, 5 microM EPA ethyl ester did not alter INa,alpha (8 +/- 4%, n = 8, P > 0.05). The present data demonstrate that free fatty acids suppress INa,alpha with high "binding affinity" to hH1alpha channels in the inactivated state and prolong the duration of recovery from inactivation.

Dietary n-3 fatty acids in the prevention of cardiac arrhythmias

It has been shown that in animals, and probably in humans, n-3 polyunsaturated fatty acids (PUFAs) are antiarrhythmic. We discuss recent studies on the antiarrhythmic actions of polyunsaturated fatty acids. Polyunsaturated fatty acids stabilize the electrical activity of isolated cardiac myocytes by inhibiting sarcolemmal ion channels so that a stronger electrical stimulus is required to elicit an action potential and the relative refractory period is markedly prolonged. This appears at present to be the probable major antiarrhythmic mechanism of polyunsaturated fatty acids.

Cocaine blockade of the acetylcholine-activated muscarinic K+ channel in ferret cardiac myocytes

The effects of cocaine on the acetylcholine(ACh)-activated muscarinic K+ current (IK(ACh)) were assessed with the whole-cell patch-clamp technique in single atrial and left ventricular myocytes enzymatically isolated from adult ferret hearts. The density of IK(ACh) is almost 5 times greater in atrial cells than in left ventricular myocytes. Cocaine reversibly blocked IK(ACh) in a dose-dependent manner. Methylecgonidine (MEG), the major product of pyrolysis of cocaine base, also produced similar effects on IK(ACh). The concentration to produce 50% inhibition of IK(ACh) was 25 microM and 12 microM for cocaine and MEG, respectively. Cocaine at micromolar concentrations also significantly inhibited the adenosine-activated purinergic K+ current (IK(Ado)), which has the same electrophysiological properties as IK(ACh). Furthermore, cocaine inhibited IK(ACh) activated by GTP gamma S, which evokes IK(ACh) by bypassing the muscarinic receptor and directly activating the G-protein, GK. These results suggest that cocaine-induced suppression of IK(ACh) is caused by its interactions beyond the binding site of muscarinic receptors. The antimuscarinic effect of cocaine may play an important role in cocaine cardiotoxicity by reducing the membrane electrical stability and acting synergistically with other actions of cocaine to facilitate the occurrence of lethal cardiac arrhythmias.

Suppression of voltage-gated L-type Ca2+ currents by polyunsaturated fatty acids in adult and neonatal rat ventricular myocytes

Our recent data show that in cardiac myocytes polyunsaturated fatty acids (PUFAs) are antiarrhythmic. They reduce I(Na), shorten the action potential, shift the threshold for excitation to more positive potentials, and prolong the relative refractory period. In this study we use patch-clamp techniques in whole-cell mode and confocal Ca2+ imaging to examine the effects of PUFAs on the voltage-gated L-type Ca2+ current (I(Ca,L)), elementary sarcoplasmic reticulum Ca2+-release events (Ca2+-sparks), and [Ca2+]i transients in isolated rat ventricular myocytes. Extracellular application of eicosapentaenoic acid (EPA; C20:5 n - 3) produced a prompt and reversible concentration-dependent suppression of I(Ca,L). The concentration of EPA to produce 50% inhibition of I(Ca) was 0.8 microM in neonatal rat heart cells and 2.1 microM in adult ventricular myocytes. While the EPA induced suppression of I(Ca,L), it did not significantly alter the shape of the current-voltage relation but did produce a small, but significant, negative shift of the steady-state inactivation curve. The inhibition of I(Ca,L) was voltage- and time-dependent, but not use- or frequency-dependent. Other PUFAs, such as docosahexaenoic acid, arachidonic acid, linolenic acid, linoleic acid, conjugated linoleic acid, and eicosatetraynoic acid had similar effects on I(Ca,L) as EPA. All-trans-retinoic acid, which had been shown to suppress induced arrhythmogenic activity in rat heart cells, also produced a significant inhibition of I(Ca,L). The saturated stearic acid and the monounsaturated oleic acid had no effect on I(Ca,L). Because both I(Ca,L) and sarcoplasmic reticulum Ca2+-release underlie many cardiac arrhythmias, we examined the effects of EPA on I(Ca,L) and Ca2+-sparks. While EPA suppressed both, it did not change the temporal or spatial character of the Ca2+-sparks, nor did it alter the ability of I(Ca,L) to trigger Ca2+-sparks. We conclude that PUFAs may act as antiarrhythmic agents in vivo in normal and Ca2+-overloaded cells principally because they reduce Ca2+ entry by blocking I(Ca,L). Furthermore, PUFAs act directly to decrease I(Na) and I(Ca,L), but indirectly to reduce the [Ca2+]i transients and [Ca2+]i-activated membrane current. Although a negative inotropic action is associated with application of PUFAs, it is clear that by reducing I(Ca,L), I(Na) and Ca2+-sparks, PUFAs can reduce spontaneous extrasystoles in the heart. The mechanisms by which PUFAs act are discussed.

Electrophysiological properties of different cell types in the shark rectal gland

Electrophysiological properties of different cell types were studied in single rectal gland cells of Squalus acanthias by the whole-cell voltage clamp technique. Based on electrophysiological characteristics and primary morphological observations (light microscope, X400), three cell types (named as I, II, and III) were found in isolated fresh cells and two cell types (I and II) in primary cultured cells of the shark rectal gland (SRG). Type I cells had both Cl- (I(Cl)) and the inwardly rectifying K+ channel (I(K1)). Type II and III cells only had I(Cl) Under X400 light microscope granular materials in the cytoplasm were found in Type I and II cells, but not in Type III cells. The data from this study show that 65 % of isolated fresh SRG cells strongly expressed the K+ channel with much less amount of the Cl- channel and 35% had only I(Cl). In sharp contrast, 11% had I(K1) and I(Cl), and 89% had only I(Cl) in cultured SRG cells. Extracellular application of 10 microM forskolin significantly enhanced I(Cl) in primary cultured SRG cells. This enhancement was influenced by intracellular Ca2+ and blocked by 50 microM Ni2+. Other compounds, such as vasoactive intestinal peptide (VIP) and 8-(4-chlorophenylthio)-adenosine3':5'-cyclic monophosphate (cpt-cAMP) also enhanced I(Cl). Interestingly, cAMP and forskolin significantly inhibited I(K1) in cultured and fresh SRG cells. I(K1) was blocked by micromolar concentrations of Ba2+ and significantly altered by extracellular K+ concentrations. The present data suggest that 1) the shark rectal gland contains different cell types which may play various roles in the process of salt secretion; 2) I(Cl) and I(K1) in SRG cells are strongly modulated by cAMP, forskolin, and VIP, as well as Ca2+, K+, and Na+ ions.

Effects of 2,3-butanedione monoxime on blood pressure, myocardial Ca2+ currents, and action potentials of rats

2,3-Butanedione monoxime (BDM) has a negative inotropic effect on smooth muscles as well as the myocardium. Therefore, in the present study we compared the sensitivity to BDM of the cardiovascular system of the spontaneously hypertensive (SHR) and the normotensive Wistar-Kyoto (WKY) rat. While BDM significantly decreased the blood pressure (BP) for both strains, the SHR was significantly more responsive. Specifically, 5, 30, 100, and 200 mg/kg BDM (intravenously) reduced BP of the SHR by 9 +/- 3, 20 +/- 3, 49 +/- 5, and 63 +/- 7 mm Hg, respectively. The same doses of BDM reduced BP of the WKY by 0, 2 +/- 0.4, 18 +/- 3, and 26 +/- 3 mm Hg. The duration of the hypotensive effect of BDM was also greater for the SHR. In vitro, BDM had a greater suppressant effect on the L-type Ca2+ current (ICa(L)) of SHR ventricular myocytes; the IC50 for the suppression of ICa(L) was 17 and 29 mM for SHR and WKY ventricular myocytes, respectively. The beta-adrenergic receptor agonist isoproterenol antagonized the suppressant effect of BDM on ICa(L). Furthermore, BDM significantly reduced the duration of both spontaneous and electrically stimulated action potentials of cultured neonatal rat cardiomyocytes. Intracellular dialysis with the catalytic unit of protein kinase A antagonized BDM's effect on the action potential. These data suggest that suppression of myocardial activity contributes to the hypotensive effect of BDM. In addition, the elevated response to BDM of SHR cardiac myocytes may indicate that the conformation and/or modulation of the L-type Ca2+ channel differ for the SHR and WKY lines of rat.

Blocking effects of polyunsaturated fatty acids on Na+ channels of neonatal rat ventricular myocytes

Recent evidence indicates that polyunsaturated long-chain fatty acids (PUFAs) prevent lethal ischemia-induced cardiac arrhythmias in animals and probably in humans. To increase understanding of the mechanism(s) of this phenomenon, the effects of PUFAs on Na+ currents were assessed by the whole-cell patch-clamp technique in cultured neonatal rat ventricular myocytes. Extracellular application of the free 5,8,11,14,17-eicosapentaenoic acid (EPA) produced a concentration-dependent suppression of ventricular, voltage-activated Na+ currents (INa). After cardiac myocytes were treated with 5 or 10 microM EPA, the peak INa (elicited by a single-step voltage change with pulses from -80 to -30 mV) was decreased by 51% +/- 8% (P < 0.01; n = 10) and 64% +/- 5% (P < 0.001; n = 21), respectively, within 2 min. Likewise, the same concentrations of 4,7,10,16,19-docosahexaenoic acid produced the same inhibition of INa. By contrast, 5 and 10 microM arachidonic acid (AA) caused less inhibition of INa, but both n - 6 and n - 3 PUFAs inhibited INa significantly. A monounsaturated fatty acid and a saturated fatty acid did not. After washing out EPA, INa returned to the control level. Raising the concentration of EPA to 40 microM completely blocked INa. The IC50 of EPA was 4.8 microM. The inhibition of this Na+ channel was found to be dose and time, but not use dependent. Also, the EPA-induced inhibition of INa was voltage dependent, since 10 microM EPA produced 83% +/- 7% and 29% +/- 5% inhibition of INa elicited by pulses from -80 to -30 mV and from -150 to -30 mV, respectively, in single-step voltage changes. A concentration of 10 microM EPA shifted the steady-state inactivation curve of INa by -19 +/- 3 mV (n = 7; P < 0.01). These effects of PUFAs on INa may be important for their antiarrhythmic effect in vivo.

Activation of protein kinase A partially reverses the effects of 2,3-butanedione monoxime on the transient outward K+ current of rat ventricular myocytes

The transient outward K+ current (Ito) was assessed in single rat ventricular myocytes with the whole-cell patch-clamp technique. Extracellular application of the chemical phosphatase 2,3-butanedione monoxime (BDM) inhibited Ito in a concentration-dependent manner. The IC50 was 14 mM. The on-set of this effect occurred within 20 s after BDM application. Ito recovered almost completely at 2 min after washout of BDM. Application of 20 mM BDM shifted the steady-state inactivation curve of Ito by 9 +/- 2 mV (n = 8) in the negative direction. Addition of 5 microM isoproterenol enhanced Ito amplitude by 16.2 +/- 1.8%. This concentration of isoproterenol partially reversed the BDM-induced inhibition of Ito. Furthermore, application of 10 mM 8-bromoadenosine 3':5'-cyclic monophosphate enhanced the amplitude of Ito and also significantly reversed the BDM-induced suppression of Ito. In contrast, intracellular dialysis with guanosine 3':5'-cyclic monophosphate (cGMP, 1-10 mM) did not affect the BDM-induced inhibition of Ito. The inward rectifier K+ current (Ik1) was relatively insensitive to BDM; i.e., 20 mM BDM inhibited Ito and Ik1 to 35.5 +/- 4.3% (n = 8) and 92.9 +/- 4.0% (n = 4) of the control, respectively. These results indicate that BDM suppressed Ito but not Ik1 of rat ventricular myocytes. We attribute the BDM suppression of Ito to dephosphorylation of the channel protein.

cAMP-independent regulation of CFTR by the actin cytoskeleton

Protein kinase A (PKA)-activation of epithelial Na+ channels requires actin filaments. Mouse mammary adenocarcinoma cells expressing the human cystic fibrosis transmembrane conductance regulator (CFTR) or mock transfectants were used to determine whether CFTR is also modulated by the actin cytoskeleton. The actin filament disrupter cytochalasin D (CD; approximately 5 micrograms/ml) readily activated whole cell currents in CFTR but not in mock-transfected (MOCK) cells. Addition of actin to the cytosolic side of quiescent excised inside-out patches of CFTR but not MOCK cells also activated CFTR. The actin-activated Cl- channels (symmetrical Cl-) had a linear conductance of 9.3 pS and were inhibited by diphenylamine-2-carboxylate and monoclonal antibodies raised against CFTR. Channel activity was also blocked by addition of the actin-binding proteins deoxyribonuclease I and filamin. Incubation of CFTR cells with CD (approximately 15 micrograms/ml) for > 6 h prevented CFTR activation by the addition of either 8-bromoadenosine 3',5'-cyclic monophosphate plus forskolin under whole cell conditions or PKA under excised inside-out conditions. However, CFTR activation was restored by subsequent addition of actin. The data indicate that CFTR is regulated by actin filaments whose effect may, in turn, be associated with the PKA-dependent pathway.

Free, long-chain, polyunsaturated fatty acids reduce membrane electrical excitability in neonatal rat cardiac myocytes

Because previous studies showed that polyunsaturated fatty acids can reduce the contraction rate of spontaneously beating heart cells and have antiarrhythmic effects, we examined the effects of the fatty acids on the electrophysiology of the cardiac cycle in isolated neonatal rat cardiac myocytes. Exposure of cardiomyocytes to 10 microM eicosapentaenoic acid for 2-5 min markedly increased the strength of the depolarizing current required to elicit an action potential (from 18.0 +/- 2.4 pA to 26.8 +/- 2.7 pA, P < 0.01) and the cycle length of excitability (from 525 ms to 1225 ms, delta = 700 +/- 212, P < 0.05). These changes were due to an increase in the threshold for action potential (from -52 mV to -43 mV, delta = 9 +/- 3, P < 0.05) and a more negative resting membrane potential (from -52 mV to -57 mV, delta = 5 +/- 1, P < 0.05). There was a progressive prolongation of intervals between spontaneous action potentials and a slowed rate of phase 4 depolarization. Other polyunsaturated fatty acids--including docosahexaenoic acid, linolenic acid, linoleic acid, arachidonic acid, and its nonmetabolizable analog eicosatetraynoic acid, but neither the monounsaturated oleic acid nor the saturated stearic acid--had similar effects. The effects of the fatty acids could be reversed by washing with fatty acid-free bovine serum albumin. These results show that free polyunsaturated fatty acids can reduce membrane electrical excitability of heart cells and provide an electrophysiological basis for the antiarrhythmic effects of these fatty acids.

Elevated density and altered pharmacologic properties of myocardial calcium current of the spontaneously hypertensive rat

DESIGN

The membrane current mediated by the L-type calcium channel (ICa) was studied for myocytes isolated from the ventricle of 10- to 11-week-old spontaneously hypertensive rats (SHR).

RESULTS

Compared with age-matched normotensive Wistar-Kyoto (WKY) or Sprague-Dawley rats, the amplitude of ICa was greater for the SHR. Two observations suggest that the greater ICa of the SHR was not due to hypertrophy. First, the similarity of membrane capacitance for these three strains of rat indicated lack of hypertrophy. Secondly, the amplitude of ICa was also greater for myocytes isolated from the right ventricle of the SHR. The ICa of the SHR was more sensitive to drugs known to activate calcium channels via phosphorylation. Specifically, extracellular application of 1 mumol/l isoprenaline as well as intracellular dialysis with either 1 mmol/l cyclic AMP or with 1 mmol/l adenosine 5'-O-3-thiotriphosphate increased the mean ICa of SHR myocytes significantly more than that of WKY rat cells. The ICa of SHR myocytes was also more sensitive to BAY K 8644 and its enantiomorphs.

CONCLUSION

The present data suggest that the greater peak amplitude of ICa for SHR myocytes relative to that of myocytes of normotensive rats is due to an increase in current density and enhancement of channel phosphorylation.

Acetylcholine in the posterior hypothalamic nucleus is involved in the elevated blood pressure in the spontaneously hypertensive rat

Intravenous injection of physostigmine, 40 and 80 ug/kg, in unanesthetized normotensive rats increased systolic blood pressure (SBP) by 21 +/- 3 and 42 +/- 7 mmHg. This pressor response was 80% inhibited by intracerebroventricular (icv) injection of hemicholinium-3 (HC-3), 20 ug. Simultaneous icv injection of HC-3 and choline (365 ug) prevented the inhibition of the pressor response by HC-3. In spontaneously hypertensive rats, injection of HC-3 either icv (20 ug) or bilaterally into the posterior hypothalamic nuclei (1 ug) decreased SBP by about 40 mmHg. The effect of intrahypothalamic HC-3 was completely blocked by simultaneous injection of choline (24.3 ug) into the same site. The hypotensive effect of icv HC-3 was completely blocked by icv choline (243 ug) and was inhibited up to 60% by injections of choline (24.3 ug) into the posterior hypothalamic nuclei.

The role of M2 muscarinic receptors in the posterior hypothalamus in the pressor response to intracerebroventricularly-injected neostigmine

Injection of neostigmine into the lateral cerebral ventricle of urethane-anesthetized rats increases arterial blood pressure. Prior injection of atropine or the muscarinic M2 antagonist 4-DAMP into the posterior hypothalamic nuclei inhibited the pressor response to neostigmine by up to approximately 56%. The same maximum degree of inhibition was elicited by bilateral electrical lesions of the posterior hypothalamic nuclei. The response was not modified by intrahypothalamic injection of pirenzepine or intraventricular injection of hexamethonium, but was prevented by intraventricular injection of 4-DAMP. The results indicate that about half of the pressor response to intraventricular injection of neostigmine was mediated through M2 muscarinic receptors in the posterior hypothalamic nuclei, and the remainder through M2 muscarinic receptors in other regions of the brain.

Blockade of brain M2 muscarinic receptors lowers blood pressure in spontaneously hypertensive rats

Injections of the M2 muscarinic receptor antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP; 1.5-40 micrograms) into the cerebral ventricles of urethane-anesthetized rats caused a dose-related inhibition of the pressor response to intravenously injected physostigmine. A similar reduction was obtained with 1/80th the dose of methylatropine, but not with the selective M1 antagonist pirenzepine. Intraventricular injection of 4-DAMP (6.25-25 micrograms) caused a dose-related reduction in blood pressure in unanesthetized spontaneously hypertensive rats (SHR), but not in normotensive controls. Systolic pressure fell 42 +/- 6 mm Hg at the 25-micrograms dose. Pirenzepine did not lower blood pressure in SHR and inhibited the antihypertensive effect of 4-DAMP.

A comparison of the central and peripheral antimuscarinic effects of atropine and methylatropine injected systemically and into the cerebral ventricles

We compared the relative abilities of atropine sulfate and methylatropine, injected i.v. and into the cerebral ventricles (icv), to block pharmacological responses mediated through central and peripheral muscarinic receptors. The hypotensive response to i.v. injection of acetylcholine (peripheral muscarinic receptors) was inhibited 50% by i.v. injection of 14.3 nmol (5.5 micrograms)/kg methylatropine and 147.8n molar equivalents (50 micrograms)/kg atropine sulfate. A similar degree of inhibition followed icv injection of 49.4 nmol/kg methylatropine and 384.2 nmol equivalents/kg atropine sulfate, indicating significant leakage out of the ventricular space. The pressor response to icv injection of neostigmine (central muscarinic receptors) also was inhibited more effectively by icv methylatropine than by atropine sulfate. Methylatropine was not effective in blocking central muscarinic receptors when injected i.v.

Acoustic signals and acoustic behaviour of Chinese river dolphin (Lipotes vexillifer)

Chinese river dolphin's (Lipotes vexillifer) underwater acoustic signals can be divided into two classes, short-duration signal (pulse train or single pulses) and long-duration signal (whistle). In this paper, time waveforms of these signals are presented and the characteristics of the signals are discussed. The experimental results on this dolphin's acoustic behaviour are given. A sinusoidal pulse with duration of about 300 ms is used as the calling signal. In a certain frequency range, as soon as a calling signal is transmitted the dolphin answers with 2 or 3 whistles. The frequency range of sensitive response is from 4 to 7 KHz, in which the answering rate reaches 100%. When the dolphin's acoustic signals recorded on the tape are transmitted into the water it swims directly toward the transducer. When noise and music are transmitted the dolphin does not respond at all.