ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractHeart failure represents an enormous clinical challenge in need of effective therapeutic approaches. The possibility of gene therapy for heart failure merits consideration at this time because of improvements in vector technology; cardiac gene delivery; and, most importantly, our understanding of the molecular pathogenesis of heart failure. We will first review recent advances in cardiac gene delivery in animal models and then examine several targets being considered for therapeutic intervention. In this context, gene transfer provides not only a potential therapeutic modality but also an important tool to help validate specific targets. Several interventions, particularly those enhancing sarcoplasmic calcium transport, show promise in animal models of heart failure and in myopathic cardiomyocytes derived from patients. However, bridging the gap between these basic investigative studies and clinical gene therapy remains a formidable task. Early experiments in rodents will need to be extended to large-animal models with clinical-grade vectors and delivery systems to assess both efficacy and safety. On the basis of a foundation of rigorous science and a growing understanding of heart failure pathogenesis, there is reason for cautious optimism for the future.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractExperiments were performed in isolated cat papillary muscles loaded with the pH-sensitive dye 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein in the esterified form to study the effect of endothelin-1 (ET-1) on the activity of the Na+-independent Cl−-HCO3−exchanger. Exposure to ET-1 (10 nmol/L) raised pHiby 0.13±0.03 U (P<0.05) in papillary muscles superfused with nominally HCO3−-free solution, whereas no significant change was detected under CO2/HCO3−-buffered medium. However, if ET-1 was applied to muscles pretreated with the anion exchanger inhibitor 4-acetamido-4′-isothiocyanato-stilbene-2,2′-disulfonic acid, pHiincreased by 0.09±0.02 U (P<0.05) in the presence of CO2/HCO3−buffer. The rate of pHirecovery from trimethylamine hydrochloride–induced intracellular alkaline load was enhanced so that net HCO3efflux increased about three times in the presence of ET-1 (2.74±0.25 versus 9.66±1.29 mmol · L−1· min−1at pHi7.55,P<0.05). This effect was canceled by previous exposure to either 50 nmol/L PD 142,893 (nonselective endothelin receptor blocker) or 300 nmol/L BQ 123 (selective blocker of ETAreceptors). BQ 123 also abolished angiotensin II–induced activation of the Na+independent Cl−-HCO3−exchanger. These results show that ET-1 increases the activity of the Na+-independent Cl−-HCO3−exchanger in cardiac tissue through the ETAreceptors. Furthermore, our data suggest that the previously described angiotensin II–induced stimulation of the anion exchanger activity is mediated by endogenous ET-1.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractUnder Na+-free conditions, low-voltage–activated Ca2+currents in cardiomyocytes from various species have been described either as Ni2+-sensitive T-type Ca2+current (ICa(T)) or as tetrodotoxin (TTX)-sensitive Ca2+current (ICa(TTX)). So far, coexistence of the 2 currents within the same type of myocyte has never been reported. We describe experimental conditions under whichICa(T)andICa(TTX)can be separated and studied in the same cell. Rat and guinea pig ventricular myocytes were investigated with the whole-cell voltage-clamp technique in Na+-free solutions. Whereas rat myocytes lackICa(T)and exhibitICa(TTX)only, guinea pig myocytes possess both of these low-voltage–activated Ca2+currents, which are separated pharmacologically by superfusion with TTX or Ni2+.ICa(T)andICa(TTX)were of similar amplitude but significantly differed in their electrophysiological properties:ICa(TTX)activated at more negative potentials than didICa(T), the potential for half-maximum steady-state inactivation was more negative, and current deactivation and recovery from inactivation were faster.ICa(TTX)but notICa(T)increased after membrane rupture (“run-up”). Isolation ofICa(TTX)by application of the bivalent cation Ni2+is critical because of possible shifts in voltage dependence. Therefore, we investigated whether the T-type Ca2+channel blocker mibefradil (10 &mgr;mol/L) is a suitable tool for the study ofICa(TTX). However, mibefradil not only blockedICa(T)by 85±2% but also decreasedICa(TTX)by 48±8%. We conclude that under Na+-free conditionsICa(T)andICa(TTX)coexist in guinea pig ventricular myocytes and that both currents are sensitive to mibefradil. Future investigations ofICa(T)will have to consider the TTX-sensitive current component to avoid possible interference.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractCalcium channels are important targets for therapeutics, but their molecular diversity complicates characterization of these channels in native heart cells. In this study, we identify a new splice variant of a low-voltage activated, or T-type Ca2+, channel in murine atrial myocytes. To date, &agr;1G and &agr;1H are the only 2 T-type Ca2+channel isoforms found in cardiovascular tissue. We compared &agr;1G and &agr;1H channel current heterologously expressed in HEK 293 cells with T-type current from the murine atrial tumor cell, AT-1. AT-1 cell T-type current (IT) has the same voltage dependence of activation and inactivation as &agr;1G and &agr;1H. The cloned T-type channels and AT-1 T-type current share similar kinetics of macroscopic inactivation and deactivation. The kinetics of recovery from inactivation of T-type currents serves as an electrophysiological signature for T-channel isoform. &agr;1G and AT-1IThave a similar recovery from inactivation time course that is faster than that for &agr;1H. In all cases, T-type current recovers with a biexponential time course, and the relative amplitude of fast and slow time courses explains the slower &agr;1H recovery kinetics, rather than differences in the time constants of the individual transitions. Thus, the T-type channels may be an important contributor to automaticity in heart cells, and molecular diversity is reflected in the pathway of recovery from inactivation.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractIn adult rat atrial myocytes, muscarinic acetylcholine (ACh)-sensitive K+current activated by a saturating concentration of adenosine (IK(ACh),(Ado)) via A1receptors (A1Rs) amounts to only 30% of the current activated by a saturating concentration of ACh (IK(ACh),(ACh)) via muscarinic M2receptors. The half-time of activation ofIK(ACh),(Ado)on a rapid exposure to agonist was ≈4-fold longer than that ofIK(ACh),(ACh). Furthermore,IK(ACh),(Ado)never showed fast desensitization. To study the importance of receptor density for A1R-IK(ACh),(Ado)signaling, adult atrial myocytes in vitro were transfected with cDNA encoding for rat brain A1R and enhanced green fluorescent protein (EGFP) as a reporter. Whole-cell current was measured on days 3 and 4 after transfection. Time-matched cells transfected with only the EGFP vector served as controls. In ≈30% of EGFP-positive cells (group I), the density ofIK(ACh),(Ado)was increased by 72%, and its half-time of activation was reduced. Density and kinetic properties ofIK(ACh),(ACh)were not affected in this fraction. In ≈70% of transfection-positive myocytes (group II), the density ofIK(ACh),(ACh)was significantly reduced, its activation was slowed, and the fast desensitizing component was lost. Adenosine-induced currents were larger in group II than in group I, their activation rate was further increased, and a fast desensitizing component developed. These data indicate that in native myocytes the amplitude and activation kinetics ofIK(ACh),(Ado)are limited by the expression of A1R. Overexpression of A1R negatively interferes with signal transduction via the muscarinic M2receptor–linked pathway, which might reflect a competition of receptors with a common pool of G proteins. Negative interference of an overexpressed receptor with physiological regulation of a target protein by a different receptor should be considered in attempts to use receptor overexpression for gene therapy.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractConnexins have been hypothesized to play an important role in intercellular communication within the vascular wall and may provide a mechanistic explanation for conduction of vasomotor responses. To test this hypothesis, we studied the transmission of vasomotor responses in the intact skeletal muscle microcirculation of connexin40-deficient mice (Cx40−/−). Arterioles were locally stimulated with hyperpolarizing dilators (acetylcholine [ACh] as well as bradykinin [Bk]) or depolarizing K+solution, and the resulting changes in diameter were measured using a videomicroscopy technique at the site of application and up to 1.32 mm upstream. Arterial pressure was elevated 25% in Cx40−/−mice (94±5 versus 75±4 mm Hg). Vessels selected for study had equivalent basal diameter and vasomotor tone in both genotypes of mice. Vasomotion was present in small arterioles of both genotypes, but its intensity was exaggerated in Cx40−/−mice. ACh and Bk induced dilation (33% and 53%, respectively, of maximal response) at the site of application that was of similar magnitude in both genotypes. These dilations were observed to spread upstream within <1 second without significant attenuation in Cx40+/+mice. However, spreading was severely attenuated in Cx40−/−animals (11±4% versus 35±7% with ACh and 38±5% versus 60±7% with Bk in Cx40−/−and Cx40+/+, respectively;P<0.05). In contrast, conducted vasoconstrictions, induced by K+solution decreased equally with distance in both genotypes. These results support a significant role for Cx40 in vascular intercellular communication. Our observations indicate that Cx40 is required for normal transmission of endothelium-dependent vasodilator responses and may underlie altered vasomotion patterns.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractThe present study was performed to examine the hypothesis that autoregulation-related changes in renal vascular resistance (RVR) are mediated by extracellular ATP. By use of a microdialysis method, renal interstitial concentrations of ATP and adenosine were measured at different renal arterial pressures (RAPs) within the autoregulatory range in anesthetized dogs (n=12). RAP was reduced in steps from the ambient pressure (131±4 mm Hg) to 105±3 mm Hg (step 1) and 80±2 mm Hg (step 2). Renal blood flow and glomerular filtration rate exhibited efficient autoregulation in response to these changes in RAP. RVR decreased by 22±2% in step 1 (P<0.01) and 38±3% in step 2 (P<0.01). The control renal interstitial concentration of ATP was 6.51±0.71 nmol/L and decreased to 4.51±0.55 nmol/L in step 1 (P<0.01) and 2.77±0.47 nmol/L in step 2 (P<0.01). In contrast, the adenosine concentrations (117±6 nmol/L) were not altered significantly. Changes in ATP levels were highly correlated with changes in RVR (r=0.88,P<0.0001). Further studies demonstrated that stimulation of the tubuloglomerular feedback (TGF) mechanism by increasing distal volume delivery elicited with acetazolamide also led to increases in renal interstitial ATP concentrations, whereas furosemide, which is known to block TGF responses, reduced renal interstitial fluid ATP concentrations. The data demonstrate a positive relation between renal interstitial fluid ATP concentrations and both autoregulation- and TGF-dependent changes in RVR and thus support the hypothesis that changes in extracellular ATP contribute to the RVR adjustments responsible for the mechanism of renal autoregulation.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID