American Journal of Physiology最新文献

ATP-sensitive potassium (K+ATP) channels have been shown to play a role in the maintenance of basal coronary vascular tone in vivo. K+ATP channels are also involved in the coronary vasodilator response to adenosine. The aim of this study was to determine the role of K+ATP channels in local metabolically mediated increases in coronary blood flow during cardiac electrical paired pacing without catecholamine effects. In 10 anesthetized closed-chest dogs, coronary blood flow was measured in the left circumflex coronary artery, and myocardial O2 consumption was calculated using the arteriovenous O2 difference. Cardiac interstitial adenosine concentration was estimated from coronary venous and arterial plasma adenosine measurements using a previously described, multicompartmental, axially distributed, mathematical model. Paired stimulation increased heart rate from 57 to 120 beats/min, myocardial O2 consumption 88%, and coronary blood flow 76%. During K+ATP channel blockade with glibenclamide, baseline coronary blood flow decreased in relation to myocardial O2 consumption and thus coronary sinus O2 tension fell. Paired-pulse pacing with glibenclamide resulted in increases in myocardial O2 consumption and coronary blood flow similar to those during control pacing. Coronary venous and estimated interstitial adenosine concentration did not increase sufficiently to overcome the glibenclamide blockade. In conclusion, K+ATP channels are not required for locally mediated metabolic increases in coronary blood flow that accompany myocardial O2 consumption during pacing tachycardia without catecholamines, and adenosine levels do not increase sufficiently to overcome the glibenclamide blockade.

The deficiency of methionine, an essential amino acid, is associated with cardiovascular lesions. Because different types of cardiac pathologies are caused by a decrease in antioxidants, we examined the effects of methionine on myocardial antioxidant enzymes in hemodynamically assessed rats that were treated with methionine (10 mg/ml) in drinking water for 12, 24, and 48 h. Glutathione peroxidase (GSHPx) activity was significantly increased to 150.5 +/- 12.2 and 191.7 +/- 13.7% of the control value at 12 and 24 h, respectively, followed by a decline to 120 +/- 24.6% at 48 h. The mRNA levels of GSHPx at these time points were 151.2 +/- 12.0, 218.7 +/- 35.3, and 173.5 +/- 25.2%, respectively. Superoxide dismutase (SOD) activity was 144.3 +/- 3.7, 114.3 +/- 10.1, and 143.1 +/- 11. 2% at 12, 24, and 48 h, respectively. Catalase (Cat) activity was 272.4 +/- 5.4, 237.8 +/- 16.6, and 224.1 +/- 17.3% of the control value. The expression of Cat and SOD mRNA was unchanged at 12, 24, and 48 h. The lipid peroxidation was decreased by 24.4 +/- 11.2, 54. 9 +/- 0.1, and 6.4 +/- 2.1% at 12, 24, and 48 h, respectively. Methionine had no effect on the ventricular or aortic pressures, heart rate, and myocardial glutathione levels at any of the time points. The study shows that methionine has a significant effect on the myocardial antioxidant enzyme activities, and only changes in GSHPx enzyme activity correlated with the mRNA changes. These antioxidant changes may have a role in the beneficial effects of methionine in pathological rather than physiological conditions.

The effect of reduced red blood cell (RBC) deformability on microvessel recruitment attendant to a reduction in tissue PO2 was studied in rat cremaster muscle using indicator-dilution techniques. Transit times (TT) of fluorescently labeled RBCs (TTRBC) and plasma (TTPl) between functionally paired arterioles and venules were obtained from their dispersion throughout the microvascular network. Changes in PO2 were effected by superfusing the tissue with Ringer solution deoxygenated to different levels. Arteriolar blood flow (Q) was measured with the two-slit technique, and the vascular volume (V) occupied by RBCs and plasma was computed from the product of Q x TT during bolus infusions of rat and less deformable human RBCs to obtain VRBC and fluorescently labeled albumin to obtain VPl. Measurements of TTRBC and TTPl permitted computation of an average flow-weighted tissue (microvascular) hematocrit (HM) relative to systemic values (HS). During infusions of autologous rat RBCs, Q and total V increased threefold in response to hypoxia, whereas normalized RBC TT (TTRBC/TTPl) and normalized tissue hematocrit (HM/HS) did not show a significant trend, indicating an increase in the number of pathways through which the RBCs can traverse the network because of spatial recruitment of capillaries. In contrast, during infusions of human RBCs, TTRBC/TTPl and HM/HS decreased significantly in response to hypoxia. Although Q exhibited an increase similar to that during rat RBC infusions, VRBC exhibited a smaller increase compared with VPl, suggesting that reduced RBC deformability leads to a redistribution of RBCs through larger-diameter pathways within the network and exclusion of these RBCs from pathways normally recruited during hypoxia. Hence, reduced RBC deformability may adversely affect capillary recruitment and physiological mechanisms that ensure adequate delivery of oxygen to tissue.

Recent works from this laboratory demonstrated potent inhibition of Fas-induced apoptosis in alveolar epithelial cells (AECs) by the angiotensin-converting enzyme (ACE) inhibitor captopril [B. D. Uhal, C. Gidea, R. Bargout, A. Bifero, O. Ibarra-Sunga, M. Papp, K. Flynn, and G. Filippatos. Am. J. Physiol. 275 (Lung Cell. Mol. Physiol. 19): L1013-L1017, 1998] and induction of dose-dependent apoptosis in AECs by purified angiotensin (ANG) II [R. Wang, A. Zagariya, O. Ibarra-Sunga, C. Gidea, E. Ang, S. Deshmukh, G. Chaudhary, J. Baraboutis, G. Filippatos and B. D. Uhal. Am. J. Physiol. 276 (Lung Cell. Mol. Physiol. 20): L885-L889, 1999]. These findings led us to hypothesize that the synthesis and binding of ANG II to its receptor might be involved in the induction of AEC apoptosis by Fas. Apoptosis was induced in the AEC-derived human lung carcinoma cell line A549 or in primary AECs isolated from adult rats with receptor-activating anti-Fas antibodies or purified recombinant Fas ligand, respectively. Apoptosis in response to either Fas activator was inhibited in a dose-dependent manner by the nonthiol ACE inhibitor lisinopril or the nonselective ANG II receptor antagonist saralasin, with maximal inhibitions of 82 and 93% at doses of 0.5 and 5 microg/ml, respectively. In both cell types, activation of Fas caused a significant increase in the abundance of mRNA for angiotensinogen (ANGEN) that was unaffected by saralasin. Transfection with antisense oligonucleotides against ANGEN mRNA inhibited the subsequent induction of Fas-stimulated apoptosis by 70% in A549 cells and 87% in primary AECs (both P < 0.01). Activation of Fas increased the concentration of ANG II in the serum-free extracellular medium 3-fold in primary AECs and 10-fold in A549 cells. Apoptosis in response to either Fas activator was completely abrogated by neutralizing antibodies specific for ANG II (P < 0.01), but isotype-matched nonimmune immunoglobulins had no significant effect. These data indicate that the induction of AEC apoptosis by Fas requires a functional renin-angiotensin system in the target cell. They also suggest that therapeutic control of AEC apoptosis is feasible through pharmacological manipulation of the local renin-angiotensin system.

We have recently cloned and characterized a unique sodium bicarbonate cotransporter, NBC3, which unlike other members of the NBC family, is ethylisopropylamiloride (EIPA) inhibitable, DIDS insensitive, and electroneutral (A. Pushkin, N. Abuladze, I. Lee, D. Newman, J. Hwang, and I. Kurtz. J. Biol. Chem. 274: 16569-16575, 1999). In the present study, a specific polyclonal antipeptide COOH-terminal antibody, NBC3-C1, was generated and used to determine the pattern of NBC3 protein expression in rabbit kidney. A major band of approximately 200 kDa was detected on immunoblots of rabbit kidney. Immunocytochemistry of rabbit kidney frozen sections revealed specific staining of the apical membrane of intercalated cells in both the cortical and outer medullary collecting ducts. The pattern of NBC3 protein expression in the collecting duct was nearly identical to the same sections stained with an antibody against the vacuolar H+-ATPase 31-kDa subunit. In addition, the NBC3-C1 antibody coimmunoprecipitated the vacuolar H+-ATPase 31-kDa subunit. Functional studies in outer medullary collecting ducts (inner stripe) showed that type A intercalated cells have an apical Na+-dependent base transporter that is EIPA inhibitable and DIDS insensitive. The data suggest that NBC3 participates in H+/base transport in the collecting duct. The close association of NBC3 and the vacuolar H+-ATPase in type A intercalated cells suggests a potential structural/functional interaction between the two transporters.

Students can learn a great deal about the peripheral circulation when teaching is based on five building blocks: hemodynamic principles, neurohumoral control, and three elements of local control of blood flow (metabolic, myogenic, and paracrine). Study of a particular special circulation starts with the application of these building blocks in the context of the function of that tissue. For example, control of skin blood flow is largely concerned with regulation of body temperature (neurohumoral control) and the response to injury (paracrine control). Regulation of coronary blood flow is almost entirely a matter of meeting the metabolic needs of the myocardium (metabolic control). By mixing and matching the five building blocks and keeping in mind the special functions of a particular tissue, students can master the peripheral circulation efficiently.

New methods in molecular biology and genetics have made possible many of the dramatic advances in physiological research that have occurred in recent years. For those of us who spend most of our time in the research laboratory, it si sometimes difficult to avoid a research-oriented, reductionist mind-set when discussing physiology with students. This article illustrates, with a few examples, the importance of conveying a "big picture" conceptual framework before discussing the details of cardiovascular physiology. Also, I have chosen examples from cardiac output and blood pressure regulation that show the importance of discussing cardiovascular physiology in terms of feedback control systems and integrating information from other areas, such as renal and endocrine physiology. Finally, I have highlighted the importance of two principles that I believe are often underemphasized in teaching physiology: mass balance and time dependence of physiological control systems.

The teaching of research design and data analysis to our graduate students has been a persistent problem. A course is described in which students, early in their graduate training, obtain extensive practice in designing experiments and interpreting data. Lecture-discussions on the essentials of biostatistics are given, and then these essentials are repeatedly reviewed by illustrating their applications and misapplications in numerous research design problems. Students critique these designs and prepare similar problems for peer evaluation. In most problems the treatments are confounded by extraneous variables, proper controls may be absent, or data analysis may be incorrect. For each problem, students must decide whether the researchers' conclusions are valid and, if not, must identify a fatal experimental flaw. Students learn that an experiment is a well-conceived plan for data collection, analysis, and interpretation. They enjoy the interactive evaluations of research designs and appreciate the repetitive review of common flaws in different experiments. They also benefit from their practice in scientific writing and in critically evaluating their peers' designs.