Sulayma Albarwani

Voltage‐gated K+ channels in rat small cerebral arteries: molecular identity of the functional channels

Voltage‐gated potassium (KV) channels represent an important dilator influence in the cerebral circulation, but the composition of these tetrameric ion channels remains unclear. The goals of the present study were to evaluate the contribution of KV1 family channels to the resting membrane potential and diameter of small rat cerebral arteries, and to identify the α‐subunit composition of these channels using patch‐clamp, molecular and immunological techniques. Initial studies indicated that 1 μmol l−1 correolide (COR), a specific antagonist of KV1 channels, depolarized vascular smooth muscle cells (VSMCs) in pressurized (60 mmHg) cerebral arteries from ‐55 ± 1 mV to ‐34 ± 1 mV, and reduced the resting diameter from 152 ± 15 μm to 103 ± 20 μm. In patch clamped VSMCs from these arteries, COR‐sensitive KV1 current accounted for 65 % of total outward KV current and was observed at physiological membrane potentials. RT‐PCR identified mRNA encoding each of the six classical KV1 α‐subunits, KV1.1‐1.6, in rat cerebral arteries. However, only the KV1.2 and 1.5 proteins were detected by Western blot. The expression of these proteins in VSMCs was confirmed by immunocytochemistry and co‐immunoprecipitation of KV1.2 and 1.5 from VSMC membranes suggested KV1.2/1.5 channel assembly. Subsequently, the pharmacological and voltage‐sensitive properties of KV1 current in VSMCs were found to be consistent with a predominant expression of KV1.2/1.5 heterotetrameric channels. The findings of this study suggest that KV1.2/1.5 heterotetramers are preferentially expressed in rat cerebral VSMCs, and that these channels contribute to the resting membrane potential and diameter of rat small cerebral arteries.

Heritability of Determinants of the Metabolic Syndrome among Healthy Arabs of the Oman Family Study

The metabolic syndrome, as defined by the International Diabetes Federation, was investigated in five large, extended, highly consanguineous, healthy Omani Arab families of a total of 1277 individuals. Heritability (h2) of the phenotypic abnormalities that make up the syndrome and other related traits was estimated by variance decomposition method using SOLAR software. The overall prevalence of the syndrome was 23%. The prevalence of abnormalities making the syndrome in a descending order were: obligatory waist circumference, hypertension, raised fasting blood glucose, low serum high‐density lipoprotein (HDL), and raised serum triglycerides (TGs). Highly significant, but widely spread, h2 values were obtained for: height (0.68), weight (0.68), BMI (0.68), serum HDL (0.63), serum leptin (0.55), percentage body fat (0.53), total serum cholesterol (0.53), fasting serum insulin (0.51), homeostasis model assessment‐insulin resistance index (0.48), serum TG (0.43), waist circumference (0.40), diastolic blood pressure (0.38), and 2‐hour glucose level (0.17), whereas for the metabolic syndrome itself, h2 was 0.38. The wide spread of h2 results (0.07 to 0.68) indicates that some determinants, such as weight, BMI, and HDL level, are under significant genetic influence among the Omani Arabs. Other determinants such as insulin resistance, abdominal obesity, diastolic blood pressure, and TG levels seem to be more environmentally driven.

Freshly isolated bovine coronary endothelial cells do not express the BKCa channel gene

Recent reports have suggested that different types of Ca2+‐activated K+ channels may be selectively expressed either in the vascular endothelial cells (ECs) or smooth muscle cells (SMCs) of a single artery. In this study, we directly compared mRNA, protein and functional expression of the high‐conductance Ca2+‐activated K+ (BKCa) channel between freshly isolated ECs and SMCs from bovine coronary arteries. Fresh ECs and SMCs were enzymatically isolated, and their separation verified by immunofluorescent detection of α‐actin and platelet/endothelium cell adhesion molecule (PECAM) proteins, respectively. Subsequently, studies using a sequence‐specific antibody directed against the pore‐forming α‐subunit of the BKCa channel only detected its expression in the SMCs, whereas PECAM‐positive ECs were devoid of the α‐subunit protein. Additionally, multicell RT‐PCR performed using cDNA derived from either SMCs or ECs only detected mRNA encoding the BKCaα‐subunit in the SMCs. Finally, whole‐cell recordings of outward K+ current detected a prominent iberiotoxin‐sensitive BKCa current in SMCs that was absent in ECs, and the BKCa channel opener NS 1619 only enhanced K+ current in the SMCs. Thus, bovine coronary SMCs densely express BKCa channels whereas adjacent ECs in the same artery appear to lack the expression of the BKCa channel gene. These findings indicate a cell‐specific distribution of Ca2+‐activated K+ channels in SMCs and ECs from a single arterial site.

Exercise training attenuates ageing-induced BKCa channel downregulation in rat coronary arteries.

Physical inactivity and ageing are widely recognized as risk factors for development of coronary artery disease. One of the characteristic changes that occurs in aged coronary artery is downregulation of their large‐conductance voltage‐ and calcium‐activated K+ (BKCa) channels. In this study, we investigated the effects of moderate exercise training (ET) on the activity of BKCa channels in coronary arteries of aged rats. Old Fischer 344 rats (23–26 months old) were randomly assigned to sedentary (O‐SED, n= 24) or exercise‐trained groups (O‐ET, n= 28). The O‐ET rats underwent a progressive treadmill exercise‐training programme for 60 min day−1, 5 days week−1 for 12 weeks. Young animals were used for comparison. Coronary arteries were mounted on a wire myograph, and contractions in response to 1, 10, 30, 50 and 100 nmol l−1 iberiotoxin were compared. Iberiotoxin (100 nmol l−1) contracted coronary arteries of young, O‐SED and O‐ET rats by 115 ± 14, 36 ± 5.6 and 61 ± 5% of 5‐hydroxytryptamine‐induced contractions, respectively. Patch‐clamp studies revealed a larger magnitude of BKCa current in young (104 ± 15.6 pA pF−1) compared with O‐ET (44 ± 9 pA pF−1) and least in O‐SED coronary smooth muscle cells (8.6 ± 2 pA pF−1). Western immunoblotting was performed to study expression levels of BKCa channel proteins. The α and β1 subunits of the BKCa channel were reduced by 40 ± 3.5 and 30 ± 2.6%, respectively, in coronary arteries of old compared with young rats, and ET attenuated this reduction in expression level to 28 ± 2 and 12 ± 4%, respectively. Our results showed that ageing was associated with a reduction in BKCa channels, and ET partly reversed this reduction. We conclude that low‐intensity ET may be beneficial in restoring age‐related decline in coronary vasodilatory properties mediated by BKCa channels.

Loss of cerebrovascular Shaker-type K+ channels: a shared vasodilator defect of genetic and renal hypertensive rats

The cerebral arteries of hypertensive rats are depolarized and highly myogenic, suggesting a loss of K(+) channels in the vascular smooth muscle cells (VSMCs). The present study evaluated whether the dilator function of the prominent Shaker-type voltage-gated K(+) (K(V)1) channels is attenuated in middle cerebral arteries from two rat models of hypertension. Block of K(V)1 channels by correolide (1 micromol/l) or psora-4 (100 nmol/l) reduced the resting diameter of pressurized (80 mmHg) cerebral arteries from normotensive rats by an average of 28 +/- 3% or 26 +/- 3%, respectively. In contrast, arteries from spontaneously hypertensive rats (SHR) and aortic-banded (Ao-B) rats with chronic hypertension showed enhanced Ca(2+)-dependent tone and failed to significantly constrict to correolide or psora-4, implying a loss of K(V)1 channel-mediated vasodilation. Patch-clamp studies in the VSMCs of SHR confirmed that the peak K(+) current density attributed to K(V)1 channels averaged only 5.47 +/- 1.03 pA/pF, compared with 9.58 +/- 0.82 pA/pF in VSMCs of control Wistar-Kyoto rats. Subsequently, Western blots revealed a 49 +/- 7% to 66 +/- 7% loss of the pore-forming alpha(1.2)- and alpha(1.5)-subunits that compose K(V)1 channels in cerebral arteries of SHR and Ao-B rats compared with control animals. In each case, the deficiency of K(V)1 channels was associated with reduced mRNA levels encoding either or both alpha-subunits. Collectively, these findings demonstrate that a deficit of alpha(1.2)- and alpha(1.5)-subunits results in a reduced contribution of K(V)1 channels to the resting diameters of cerebral arteries from two rat models of hypertension that originate from different etiologies.

Mathematical biomarkers for the autonomic regulation of cardiovascular system

Heart rate and blood pressure are the most important vital signs in diagnosing disease. Both heart rate and blood pressure are characterized by a high degree of short term variability from moment to moment, medium term over the normal day and night as well as in the very long term over months to years. The study of new mathematical algorithms to evaluate the variability of these cardiovascular parameters has a high potential in the development of new methods for early detection of cardiovascular disease, to establish differential diagnosis with possible therapeutic consequences. The autonomic nervous system is a major player in the general adaptive reaction to stress and disease. The quantitative prediction of the autonomic interactions in multiple control loops pathways of cardiovascular system is directly applicable to clinical situations. Exploration of new multimodal analytical techniques for the variability of cardiovascular system may detect new approaches for deterministic parameter identification. A multimodal analysis of cardiovascular signals can be studied by evaluating their amplitudes, phases, time domain patterns, and sensitivity to imposed stimuli, i.e., drugs blocking the autonomic system. The causal effects, gains, and dynamic relationships may be studied through dynamical fuzzy logic models, such as the discrete-time model and discrete-event model. We expect an increase in accuracy of modeling and a better estimation of the heart rate and blood pressure time series, which could be of benefit for intelligent patient monitoring. We foresee that identifying quantitative mathematical biomarkers for autonomic nervous system will allow individual therapy adjustments to aim at the most favorable sympathetic-parasympathetic balance.

Ca(2+)‐activated Cl‐ and K+ channels and their modulation by endothelin‐1 in rat pulmonary arterial smooth muscle cells

Using the patch‐clamp recording technique, we observed that endothelin‐1 (ET‐1; 0.8‐16 nM) enhanced a voltage‐activated outward current (Iout) and induced periodic oscillations of inward current in smooth muscle cells isolated from small pulmonary arteries (200‐400 microns in diameter). Anion substitution experiments revealed that the ET‐1‐induced inward current was carried by Cl‐ ions. Application of bosentan (10 microM; and ETA and ETB receptor antagonist) and FR 139317 (1‐10 microM; a selective ETA receptor antagonist) prevented initiation of inward currents or enhancement of Iout by ET‐1. The ETB receptor agonist tetra‐Ala‐endothelin‐1 (1‐20 nM) failed to evoke these responses. Caffeine (10 mM) induced a single transient inward current and prevented any further activation of inward current, or enhancement of Iout, by subsequent application of 16 nM ET‐1, suggesting that these currents were mediated by Ca2+ release from internal stores. Rapid intracellular release of Ca2+ by photolysis of nitr‐5 activated an inward Cl‐ current and increased the magnitude of Iout. These results demonstrate the existence of Ca(2+)‐activated Cl‐ and K+ channels in pulmonary arterial smooth muscle. The physiological role of these channels is at present uncertain, although their activation may be involved in the contractile responses of pulmonary arterial smooth muscle to ET‐1.

Non-dipping blood pressure in the metabolic syndrome among Arabs of the Oman family study.

Objective: The objective was to examine the circadian changes in blood pressure and their relation to the metabolic syndrome and its components in Omani Arabs.

Effects of overweight and leisure-time activities on aerobic fitness in urban and rural adolescents.

BACKGROUND The aim of this research was to study the effects of overweight and leisure-time activities on maximal aerobic capacity (VO(2)max) in urban and rural Omani adolescents. METHODS A total of 529 (245 males, 284 females) adolescents, aged 15-16 years were randomly selected from segregated urban and rural schools. Maximal aerobic capacity was estimated using the multistage 20-meter shuttle-run test. RESULTS The body mass index (BMI) of urban boys and girls was significantly higher than that of rural boys and girls. Urban boys and girls spent significantly less weekly hours on sports activities and significantly more weekly hours on TV/computer games than their rural counterpart. Urban boys and girls achieved significantly less VO(2)max than rural boys and girls (44.2 and 33.0 vs. 48.3 and 38.6 mL/kg/min, respectively). Maximal aerobic capacity was negatively correlated with BMI in urban boys. CONCLUSION Overweight and inactivity had significant negative effects on cardiorespiratory fitness in urban boys and girls as compared to their rural counterparts. Weight gain in adolescence requires early intervention.

Association of adiponectin promoter variants with traits and clusters of metabolic syndrome in Arabs: Family-based study

Plasma levels of adiponectin are decreased in type 2 diabetes, obesity and hypertension. Our aim was to use a family-based analysis to identify the genetic variants of the adiponectin (ADIPOQ) gene that are associated with obesity, insulin resistance, dyslipidemia and hypertension, among Arabs. We screened 328 Arabs in one large extended family for single nucleotide polymorphisms (SNPs) in the promoter region of the ADIPOQ gene. Two common SNPs were detected: rs17300539 and rs266729. Evidences of association between traits related to the metabolic syndrome and the SNPs were studied by implementing quantitative genetic association analysis. Results showed that SNP rs266729 was significantly associated with body weight (p-value=0.001), waist circumference (p-value=0.037), BMI (p-value=0.015) and percentage of total body fat (p-value=0.003). Up to 4.1% of heritability of obesity traits was explained by the rs266729 locus. Further cross-sectional analysis showed that carriers of the G allele had significantly higher values of waist circumference, BMI and percentage of total body fat (p-values 0.014, 0.004 and 0.032, respectively). No association was detected between SNP rs266729 and other clusters of metabolic syndrome or their traits except for HOMA-IR and fasting plasma insulin levels, p-values 0.035 and 0.004, respectively. In contrast, both measured genotype and cross-sectional analysis failed to detect an association between the SNP rs17300539 with traits and clusters of metabolic syndrome. In conclusion, we showed family-based evidence of association of SNP rs266729 at ADIPOQ gene with traits defining obesity in Arab population. This is important for future prediction and prevention of obesity in population where obesity is in an increasing trend.