Arachidonic acid modulates the spatiotemporal characteristics of agonist-evoked Ca2+ waves in mouse pancreatic acinar cells

In pancreatic acinar cells analysis of the propagation speed of secretagogue-evoked Ca2+ waves can be used to examine coupling of hormone receptors to intracellular signal cascades that cause activation of protein kinase C or production of arachidonic acid (AA). In the present study we have investigated the role of cytosolic phospholipase A2 (cPLA2) and AA in acetylcholine (ACh)- and bombesin-induced Ca2+ signaling. Inhibition of cPLA2 caused acceleration of ACh-induced Ca2+ waves, whereas bombesin-evoked Ca2+ waves were unaffected. When enzymatic metabolization of AA was prevented with the cyclooxygenase inhibitor indomethacin or the lipoxygenase inhibitor nordihydroguaiaretic acid, ACh-induced Ca2+ waves were slowed down. Agonist-induced activation of cPLA2 involves mitogen-activated protein kinase (MAPK) activation. An increase in phosphorylation of p38(MAPK) and p42/44(MAPK) within 10 s after stimulation could be demonstrated for ACh but was absent for bombesin. Rapid phosphorylation of p38(MAPK) and p42/44(MAPK) could also be observed in the presence of cholecystokinin (CCK), which also causes activation of cPLA2. ACh-and CCK-induced Ca2+ waves were slowed down when p38(MAPK) was inhibited with SB 203580, whereas inhibition of p42/44(MAPK) with PD 98059 caused acceleration of ACh- and CCK-induced Ca2+ waves. The spreading of bombesin-evoked Ca2+ waves was affected neither by PD 98059 nor by SB 203580. Our data indicate that in mouse pancreatic acinar cells both ACh and CCK receptors couple to the cPLA2 pathway. cPLA2 activation occurs within 1-2 s after hormone application and is promoted by p42/44(MAPK) and inhibited by p38(MAPK). Furthermore, the data demonstrate that secondary (Ca2+-induced) Ca2+ release, which supports Ca2+ wave spreading, is inhibited by AA itself and not by a metabolite of AA.

Decreased prevalence of Alzheimer disease associated with 3-hydroxy-3-methyglutaryl coenzyme A reductase inhibitors

CONTEXT

Increasing evidence suggests that cholesterol plays a role in the pathophysiology of Alzheimer disease (AD). For instance, an elevated serum cholesterol level has been shown to be a risk factor for AD.

OBJECTIVE

To determine whether patients taking 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins), which are a group of medicines that inhibit the synthesis of cholesterol, have a lower prevalence of probable AD.

DESIGN

The experiment uses a cross-sectional analysis comparing the prevalence of probable AD in 3 groups of patients from hospital records: the entire population, patients receiving 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (hereafter referred to as the statins), and patients receiving medications used to treat hypertension or cardiovascular disease.

PATIENTS

The subjects studied were those included in the computer databases of 3 different hospitals for the years October 1, 1996, through August 31, 1998.

MAIN OUTCOME MEASURES

Diagnosis of probable AD.

RESULTS

We find that the prevalence of probable AD in the cohort taking statins during the study interval is 60% to 73% (P < .001) lower than the total patient population or compared with patients taking other medications typically used in the treatment of hypertension or cardiovascular disease.

CONCLUSIONS

There is a lower prevalence of diagnosed probable AD in patients taking 2 different 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors-lovastatin and pravastatin. While one cannot infer causative mechanisms based on these data, this study reveals an interesting association in the data, which warrants further study. Arch Neurol. 2000;57:1439-1443

Office-based laser assisted tympanic membrane fenestration in adults and children: pilot data to support an alternative to traditional approaches to otitis media

OBJECTIVES

To determine the role of intermediate duration ( approximately 3 weeks) middle ear ventilation using office-based laser assisted tympanic membrane fenestration in resolving an episode of otitis media with effusion in adults and children who otherwise would have been treated with insertion of pressure equalization tubes.

METHODS

A retrospective chart review of 92 patients (162 ears) was conducted to identify the utility and technical challenges associated with laser assisted tympanic membrane fenestration in an office setting. Clinical characteristics reviewed included: age, gender, duration of effusion, season performed, and hearing and health status of middle ear upon healing of the fenestration.

RESULTS

69% of all patients were effusion free upon closure of the fenestration; 68% of those <3 years; 70% of those 3-7 years; and 70% of those 25-80 years. Some episodes recurred and at final follow-up 64% had normal middle ear structure and function (range of follow-up =1-18 months, mean 2.5 months, median 2.0). Shorter duration of effusion pre-fenestration was more often associated with return to normal middle ear structure and function (P<0.01). Season performed, number of previous episodes of otitis media and pre-treatment tympanometry were not predictive of result. No significant complications were observed.

CONCLUSIONS

The use of office-based laser assisted tympanic membrane fenestration is a reasonably safe and effective procedure for the treatment of otitis media in most adults and children. As a minimally invasive otologic procedure, laser assisted tympanic membrane fenestration has great potential to decrease the rates of both antibiotic usage and insertion of ear tubes.

Ellipsometry Studies of Lipoprotein Adsorption

The adsorption of a number of lipoproteins, i.e., low-density lipoprotein (LDL), oxidized LDL (oxLDL), high-density lipoprotein (HDL), and lipoprotein (a), at silica and methylated silica as well as at the latter surface modified through adsorption of proteoheparan sulfate, was investigated with in situ ellipsometry at close to physiological conditions. It was found that LDL, oxLDL, HDL, and lipoprotein (a) all adsorbed more extensively at silica than at methylated silica. Upon exposure of the methylated silica surface to proteoheparan sulfate, this proteoglycan adsorbs through its hydrophobic moiety, thereby forming a layer similar to that in the biological system, with the polysaccharide chains forming brushes oriented toward the aqueous solution. Analogous to the biological system, both lipoprotein (a) and LDL were found to deposit at such surfaces, the latter particularly in the simultaneous presence of Ca(2+). After HDL pre-exposure, however, no LDL deposition was observed, even at high LDL and Ca(2+) concentrations. These findings correlate well with those obtained from clinical investigations on risk factors for atherosclerosis. Copyright 2000 Academic Press.

Development of a method to analyze orthopaedic practice expenses

The purpose of the current investigation was to present a standard method by which an orthopaedic practice can analyze its practice expenses. To accomplish this, a five-step process was developed to analyze practice expenses using a modified version of activity-based costing. In this method, general ledger expenses were assigned to 17 activities that encompass all the tasks and processes typically performed in an orthopaedic practice. These 17 activities were identified in a practice expense study conducted for the American Academy of Orthopaedic Surgeons. To calculate the cost of each activity, financial data were used from a group of 19 orthopaedic surgeons in Houston, Texas. The activities that consumed the largest portion of the employee work force (person hours) were service patients in office (25.0% of all person hours), maintain medical records (13.6% of all person hours), and resolve collection disputes and rebill charges (12.3% of all person hours). The activities that comprised the largest portion of the total expenses were maintain facility (21.4%), service patients in office (16.0%), and sustain business by managing and coordinating practice (13.8%). The five-step process of analyzing practice expenses was relatively easy to perform and it may be used reliably by most orthopaedic practices.

[Pleiotropic effects of garlic]

Garlic as a herbal remedy reduces a multitude of risk factors which play a decisive role in the genesis and progression of arteriosclerosis: decrease in total and LDL-cholesterol, increase in HDL-cholesterol, reduction of serum triglyceride and fibrinogen concentration, lowering of arterial blood pressure and promotion of organ perfusion, and, finally, enhancement in fibrinolysis, inhibition of platelet aggregation, and diminution of plasma viscosity. In a prospective, 4-year clinical trial with primary endpoint 'arteriosclerotic plaque volume' it was proven not only a 9 to 18% reduction and 3% regression in plaque volume of the total collective under the influence of standardized garlic powder dragees (900 mg/die LI 111), but also of some facets of the phytopharmacologic pleiotropy of this herb: decrease in LDL level by 4%, increase in HDL concentration by 8%, and lowering in blood pressure by 7%. The reduction of arterial blood pressure is due to an additional opening of K(Ca) ion channels in the membrane of vascular smooth muscle cells that effects its hyperpolarization. This membrane hyperpolarization closes about 20% of the L-type Ca2+ channels, consequence of which is vasodilatation. In human coronary arteries, the increase in vascular diameter by 4% is closely associated with an improvement of coronary perfusion by 18%. These pleiotropic effects of garlic result in a reduction of relative cardiovascular risk for infarction and stroke by more than 50%.

Using activity-based costing to track resource use in group practices

Research shows that understanding how resources are consumed can help group practices control costs. An American Academy of Orthopaedic Surgeons study used an activity-based costing (ABC) system to measure how resources are consumed in providing medical services. Teams of accounting professors observed 18 diverse orthopedic surgery practices. The researchers identified 17 resource-consuming business processes performed by nonphysician office staff. They measured resource consumption by assigning costs to each process according to how much time is spent on related work activities. When group practices understand how their resources are being consumed, they can reduce costs and optimize revenues by making adjustments in how administrative and clinical staff work.

Oxygen-dependent regulation of membrane potential and vascular tone of human umbilical vein

OBJECTIVE

We question the hypothesis that vascular tone of human umbilical vein is insensitive to oxygen pressure and minimal already at resting conditions.

STUDY DESIGN

Isometric tension and intracellular membrane potential of native (n = 7) and endothelium-denuded (n = 7) human umbilical vein strips were recorded simultaneously at oxygen pressure values of 5 to 104 mm Hg.

RESULTS

Increasing oxygen pressure from 5 to 104 mm Hg led to graded membrane depolarization from -58.2 +/- 1.3 mV (SEM) to -54.0 +/- 0.7 mV (P <.009) and increased isometric tension from 0.576 +/- 0.016 g to 0.790 +/- 0.032 g (P <.0001). The steepest increase in tension (Delta = 0.063 g) occurred within the physiologic intrauterine oxygen tension range (27-35 mm Hg). Isometric tension at hypoxia (partial oxygen pressure, 5 mm Hg) corresponded to 88% of resting tension. Tension and membrane potential were related linearly (r(2) = 0.99). Disruption of the endothelium reversed the effects of oxygen pressure.

CONCLUSION

Human umbilical vein vascular tone was regulated by oxygen tension and showed a hypoxic vasodilator reserve. Oxygen-dependent effects were related to the membrane potential and required the endothelium.

Physicochemical binding properties of the proteoglycan receptor for serum lipoproteins

Proteoheparan sulfate can be adsorbed to a methylated silica surface in a monomolecular layer via its transmembrane hydrophobic protein core domain. Due to electrostatic repulsion, its anionic polysugar side chains are stretched out into the blood substitute solution representing a co-receptor for specific lipoprotein binding through basic amino acid-rich residues within their apolipoproteins. The binding process was studied by ellipsometric techniques showing that oxLDL had a deleterious effect on heparan sulfate proteoglycan binding and conformation. Ca2+ binding to and storage on the proteoheparan sulfate/LDL compound formed a 'heterotrimeric' HS-PG/LDL/Ca2+ complex of high stability, aggregability and deposit coating. On the other hand, HDL bound to heparan sulfate proteoglycan protected against LDL docking and completely suppressed calcification of the proteoglycan/lipoprotein complex.

The antiatherosclerotic effect of Allium sativum

In a randomized, double-blind, placebo-controlled clinical trial, the plaque volumes in both carotid and femoral arteries of 152 probationers were determined by B-mode ultrasound. Continuous intake of high-dose garlic powder dragees reduced significantly the increase in arteriosclerotic plaque volume by 5-18% or even effected a slight regression within the observational period of 48 months. Also the age-dependent representation of the plaque volume shows an increase between 50 and 80 years that is diminished under garlic treatment by 6-13% related to 4 years. It seems even more important that with garlic application the plaque volume in the whole collective remained practically constant within the age-span of 50-80 years. These results substantiated that not only a preventive but possibly also a curative role in arteriosclerosis therapy (plaque regression) may be ascribed to garlic remedies.

Manage indirect practice expense the way you practice medicine: with information

PURPOSE

Surgeons are increasingly faced with the pressures of maintaining the highest quality of patient care, while at the same time maintaining financial viability. The purpose of this project was to provide a framework for analyzing practice costs for colorectal surgeons using an activity-based cost accounting model.

METHODS

A survey of 11 practices that were diverse in terms of geography, managed care penetration, academic vs. private practice style, and case distribution was performed. In activity-based costing the assignment of typical costs such as staff salaries are assigned to the appropriate business process. The business processes employed in this study were service patients in the office, perform in-office procedures, schedule cases in facilities, service patients in the hospital, insurance authorization, maintain medical records, billing, collections, resolve billing disputes, interaction with third parties, maintain professional education, sustain and manage the practice, maintain the facility, teaching and research, and performing drug studies. The final step is to assign the cost associated with all appropriate business processes to the appropriate cost object. The cost objects in this study were defined as a charge office visit, no-charge office visit, charge hospital visit, in-office procedures, in-facility procedures, and performing drug studies. The data were then analyzed to allow a comparison of four similar practices within the study group.

RESULTS

The data demonstrated that the cost of seeing a charge office visit ranged from $55 to $105. Similarly, the cost of seeing a no-charge office visit during the global period ranged from $43 to $100. The study analyzed possible explanations for the wide variability in these costs.

CONCLUSIONS

It is essential that physicians clearly understand the sources of expenses generated by the operation of their practices. A clear comprehension of costs will lead colorectal surgeons to make appropriate decisions regarding such important issues as office staffing ratios, office square footage, and instrumentation acquisitions.

Tumor cell locomotion and metastatic spread

The cytoskeletal filament proteins alpha-actinin, filamin, desmin, and filamin-desmin aggregates were adsorbed to a hydrophobic silica surface. The adsorbed amount as measured by ellipsometric methods after rinsing and equilibration was 2.7 mg/m2 for alpha-actinin and 0.4 mg/m2 for filamin plus desmin, respectively. Adsorbed layer thicknesses in physiological salt solution were about 107 nm, 89 nm, 108 nm and 93 nm for alpha-actinin, filamin, desmin, and cross-linked filamin-desmin, respectively. Ca2+ ions in a concentration of 10(-4), 10(-3), and 2.52 mmol/l had no effect on the adsorbed amount, refractive index, and adsorbed layer thickness of the individual intermediate filament proteins. Cross-linked filamin-desmin, however, reacted markedly upon the addition of these Ca2+ concentrations with a change in refractive index and adsorbed layer thickness. The layer formed by the filamin-desmin complex contracted by 2-3, 6-7, and 6-7 nm, respectively. The maximum shortening occurred at 1 pmol/l Ca2+. The Ca(2+)-dependent adsorbed layer changes of cross-linked filamin-desmin supports the contractile mechanisms in muscular tissues and forms the basis for migration and motility in nonmuscular cells. These motional events are crucially involved in peripheral organ perfusion, inflammation, and tumor invasion and metastasis.

Middle ear laser office ventilation (LOV) with a CO2 laser flashscanner

BACKGROUND

Laser assisted ventilation of the middle ear with a defocused laser beam has been performed on adults in an office setting without anesthesia.

OBJECTIVE

The purpose of this study was to evaluate the efficacy and safety of a highly controlled, char-free CO2 flashscanner technology for the ventilation of the middle ear in young children, at this stage under general anesthesia, and later without anesthesia.

METHODS

A CO2 flashscanning laser, in conjunction with a micromanipulator, was used on 21 SOM patients ages 3-7 years old, with followup at 2 months. Operating time is approximately 5 minutes.

RESULTS

Postoperative results show average patency of 2-3 weeks without adverse effects. Of the treated patients, 53% did not require a second treatment, whereas 47% still suffered from otitis media and needed a second treatment.

CONCLUSION

The CO2 flashscanner laser technology is effective and safe for middle ear ventilation and provides excellent control of the perforation diameter. It is already being performed in an office setting with sedation on a limited basis with very promising preliminary results. Based on the current study and on 70 additional cases with longer interval followup, we anticipate the office technique to become widely used in the future.

A comparison of clinical and ultrasonic estimation of fetal weight

OBJECTIVE

To compare the accuracy of routine ultrasonic and clinical birth weight estimation.

METHODS

The study sample included 1717 women with singleton pregnancies, admitted in early labor with an ultrasonic estimated fetal weight (EFW) performed during the preceding week. Clinical EFW was obtained before rupture of the membranes by the attending senior resident, who was unaware of the ultrasonic EFW. Accuracy was determined by the percentage error, the absolute percentage error, and the proportion of estimates within 10% of the actual birth weight (birth weight +/- 10%). Statistical analysis was done by the paired t test, the comparison of correlated variances, the Wilcoxon sign test, and the chi2 test. Actual birth weight in the study sample averaged 3334+/-607 g (+/- standard deviation, [SD]) and ranged between 690 and 5320 g.

RESULTS

The means of all error terms of the clinical EFW were significantly smaller than those of the ultrasonic EFW. However, the rates of estimates within 10% of birth weight were not significantly different (72 and 69%, respectively). In birth weights less than 2500 g, both methods overestimated the birth weight, but the mean errors of the ultrasonic EFW were significantly smaller than those of the clinical EFW. The ultrasonic EFW had significantly higher rates of birth weight +/- 10% than the clinical EFW (63 compared to 49%, respectively). In the 2500-4000 g birth weight, only the clinical EFW had no systematic error, whereas the ultrasonic EFW underestimated the birth weight. The mean errors of the clinical EFW were significantly smaller and the rate of birth weight +/- 10% significantly higher than those of the ultrasonic EFW. In the birth weight greater than 4000 g, both methods underestimated the birth weight, and the mean errors and the rate of estimates within 10% of birth weight were similar for both methods.

CONCLUSION

Clinical estimation of birth weight in early labor is as accurate as routine ultrasonic estimation obtained in the preceding week. In the lower range of birth weight (less than 2500 g), ultrasonic estimation is more accurate; in the 2500-4000 g range, clinical estimation is more accurate. In the higher range of birth weight (greater than 4000 g), both methods have similar accuracy.

Vascular smooth muscle, a multiply feedback-coupled system of high versatility, modulation and cell-signaling variability

Under normal conditions, the various vascular regulatory effector influences are interwoven in a dynamic, and not a static, circulatory system. The reaction of a smooth muscle cell is thus reflected only incompletely by the stationary activation curve 'developed tension versus membrane potential'. The missing time domain in this relationship is a reflection of our as yet limited understanding of the system's behavior in space and time. It should be emphasized that the rhythmogenic properties of vascular smooth muscle are closely coupled to a functioning circulation. The electrical and mechanical oscillations, which can be traced back to rhythmic activity of the active, electrogenic Na+/K+ pump, could originate in the allosteric qualities of the enzyme phosphofructokinase (PFK). Thus, PFK represents a rhythmogenic enzyme which may serve as an example of the connection between the biological properties on a molecular level and the spatiotemporal system's behavior. The cardiovascular system and its rhythmicity may be dominated by only a few control points, one of which is distinguished by the viscoelastic properties of a blood flow sensor macromolecule. Therefore, the three prominent control points - PFK, (Na+ + K+)-ATPase and flow sensor conformation - acting as negatively feedback-coupled, nonlinear synergetic order parameters, are sufficient to initiate the periodic events in the cardiovascular system and to provide a plausible explanation for their causal origin.

The role of the endothelium in inflammation and tumor metastasis

In inflammation, cells interact with extracellular matrices or neighboring cells by a spatio-temporal intervention pattern of specific cell surface receptors and adhesion molecules. Resident cells of the injured tissue communicate with circulating effector cells by cytokines and direct cell-cell contact. These cytokines stimulate expression of the adhesion molecules ICAM-1, VCAM-1, and E- and P-selectin on endothelial cell surfaces and upregulate beta 2-integrins and ICAM-1 on luminal leukocytes. White blood cells then adhere to the activated endothelial cells, migrate through the vessel wall, and penetrate areas of infection or tissue damage. The basis for a cellular immune response is formed by the interaction between T lymphocytes and antigen-presenting cells amplified by adhesion molecule LFA-1,2,3 to ICAM-1 binding.

Age-dependent organotypic expression of microtubule-associated proteins (MAP1, MAP2, and MAP5) in rat brain

Age-dependent changes in the distribution of microtubule-associated proteins (MAPs) were analyzed in young (3-months, N = 3) and old (24-months, N = 3) rat brain. In the young rats, MAP1 and MAP5 exhibited prominent immunostaining in the perikarya and dendrites whereas MAP2 was selectively localized in the dendrites. In the cerebellum, MAP2 was preferentially localized in finer and distal branches of Purkinje cell dendrites and in punctate deposits surrounding glomeruli. In general, aging resulted in obvious declines in MAP2- >> MAP1- and MAP5-immunoreactivities in the hippocampus and parietal cortex but no change in cerebellum. The results indicate that: (1) hippocampus is the most affected and cerebellum is the least affected region with regard to declines in MAPs-immunoreactivities in the aged rat brain; (2) dendrite-specific MAP2 is almost completely depleted from most dendrites in the hippocampus and cortex. In summary, loss of MAP2-immunoreactivity in the affected brain areas may be associated with age-related impairment of synaptic plasticity, cognition and memory functions.

Na,K-ATPase: increases in alpha1-messenger RNA and decreases in alpha3-messenger RNA levels in aging rat cerebral cortex

Age-related changes in the expression of Na,K-ATPase catalytic (alpha) subunit isoform messenger RNAs were investigated by in situ hybridization in frontal-parietal cortex of Fischer-344 male rats. It was found that the density of alpha1-messenger RNA, present in glia and some neurons, increases dramatically in the neuropil of cortex and in the corpus callosum of the aged (24 months) as compared to young (three months) rats. In contrast, levels of alpha3-messenger RNA, which is neuron-specific, decrease dramatically over the neurons of layers III and V and retrosplenial cortex in the aged as compared to the young animals, despite no changes in cellular density. The declines in the levels of neuron-specific alpha3-messenger RNA may constitute a very early change in age-related differentiation of brain. These changes in Na,K-ATPase isoform expression may represent a candidate for an age-related factor predisposing to or potentiating certain neurodegenerative diseases.

Differential expression of Na,K-ATPase alpha-isoform mRNAs in aging rat cerebellum

Age-dependent changes in the expression of Na,K-ATPase alpha 1- and alpha 3-mRNAs were analyzed in the rat cerebellum by in situ hybridization. In young rats, alpha 1-mRNA showed prominent labeling in the granular layer (GL) with moderate fine distribution in the molecular layer (ML), Purkinje cell layer (PCL), and white matter (WM) but no clusters over Purkinje cells (PCs). In old rats, alpha 1-mRNA remained unchanged in ML and PCL, but declined by 43% (P < 0.0001) in GL and increased by 624% (P < 0.0001) in WM. alpha 3-mRNA in young rats showed large clusters of label on stellate, basket, Golgi, and PCs and fine grains diffusely in ML, GL, and WM. In old rats, alpha 3-mRNA declined by 87% in ML, 83% in PCL, 84% per PC, and 89% in GL and increased by 111% in WM (all values P < 0.0001) relative to young rats. PC numbers were reduced by 30%, but the average area of PC profiles did not change significantly. In old rats, the specific cluster-like label related to alpha 3-mRNA on PCs, stellate, basket, and Golgi cells was lost. Immunocytochemistry of cerebellum and hippocampus showed no age-related change in the distribution and density of total catalytic polypeptide. Thus, the discordance between changes in the levels of mRNAs in neuronal layers and WM in the face of constant polypeptide levels indicates age-related changes in polypeptide turnover. Cell- and isoform-specificity of alpha-isoform mRNAs in aging rat cerebellum may reflect differential regulation underlying age-related impairments in signal transduction and motor learning.

Blood-flow sensing by anionic biopolymers

Using 23Na-NMR techniques we could show that the polyanion proteoheparan sulfate integrated into the membrane of endothelial cells may serve as "flow sensor'. Based on its viscoelastic properties, heparan sulfate proteoglycan is present as a random coil under "no flow' conditions, whereby most of its polyanionic sites undergo intramolecular hydrogen bonding. With increasing flow the macromolecule becomes unfolded into a filamentous structure. Additional anionic binding sites to which Na+ ions from the blood bind are released by this shear stress-dependent conformational change. The Na+ binding triggers the signal transduction chain for a vasodilatory vessel reaction. Decrease in flow effects, for reasons of the intramolecular elastic recoil forces of the macromolecules, an entropic coiling, the release of Na+ ions and thus an interruption of the signal chain. Proteoheparan sulfate adsorbed onto a hydrophobic surface in physiological Krebs solution at pH 7.3 demonstrated clearly its characteristic as a Na+ sensor. While Ca2+ ions modulated the adsorption (promotion with increasing Ca2+ concentrations) by changing the conformation of the sensor molecule, the adsorbed amount was determined preferably by the Na+ concentration. K+ and Mg2+ ions showed slightly desorbing properties with increasing concentrations. Thus, it may be concluded that Na+ ions play the role as "first messenger' in flow-dependent vasodilation.

Anionic biopolymers as blood flow sensors

The finding of flow-dependent vasodilation rests on the basic observation that with an increase in blood flow the vessels become wider, with a decrease the vascular smooth muscle cells contract. Proteoheparan sulphate could be the sensor macromolecule at the endothelial cell membrane-blood interface, that reacts on the shear stress generated by the flowing blood, and that informs and regulates the vascular smooth muscle cells via a signal transduction chain. This anionic biopolyelectrolyte possesses viscoelastic and specific ion binding properties which allow a change of its configuration in dependence on shear stress and electrostatic charge density. The blood flow sensor undergoes a conformational transition from a random coil to an extended filamentous state with increasing flow, whereby Na+ ions from the blood are bound. Owing to the intramolecular elastic recoil forces of proteoheparan sulphate the slowing of a flow rate causes an entropic coiling, the expulsion of Na+ ions and thus an interruption of the signal chain. Under physiological conditions, the conformation and Na+ binding proved to be extremely Ca(2+)-sensitive while K+ and Mg2+ ions play a minor role for the susceptibility of the sensor. Via counterion migration of the bound Na+ ions along the sensor glycosaminoglycan side chains and following Na+ passage through an unspecific ion channel in the endothelial cell membrane, the signal transduction chain leads to a membrane depolarization with Ca2+ influx into the cells. This stimulates the EDRF/NO production and release from the endothelial cells. The consequence is vasodilation.