Human myocardial ATP content and in vivo contractile function

The study was designed to characterize the relationship between the metabolise content of human cardiac muscle and in vivo cardiac function. ATP, total adenine nucleotides, and NAD were quantified in human myocardial biopsies using high performance liquid chromatography. Right ventricular endomyocardial biopsies were obtained from 43 patients with dilated cardiomyopathy, 6 with restrictive cardiomyopathy, 10 with normal systolic and diastolic function, and from 24 cold preserved human donor hearts. Transmural samples of failing right and left ventricular free walls were obtained during cardiac transplantation surgery in 8 patients. ATP, total adenine nucleotides, and NAD were similar in the cold-preserved donor hearts and in right ventricular endomyocardial biopsies from the 10 individuals with normal systolic and diastolic function. In contrast, these values were significantly depressed in tissue samples from patients with dilated or restrictive cardiomyopathy. There was a significant correlation between ATP and pulmonary capillary wedge pressures but not ejection fractions. Declines in the sizes of myocardial ATP, adenine nucleotide, and pyridine nucleotide pools in the human myocardium are associated primarily with diastolic but not systolic dysfunction.     

Smooth muscle cell transplantation improves bladder contractile function in streptozocin-induced diabetic rats

Background aimsDamage to smooth muscle has been the primary cause of dysfunction in diabetic bladders. Major changes in the filling phase of the bladder result in the loss of compliance and incomplete emptying in patients.MethodsCell-based therapies in the lower urinary tract have shown promising results. We argue that because diabetic bladder dysfunction is primarily a problem arising out of altered smooth muscle cells (SMCs), it would be an interesting approach to introduce healthy SMCs into the bladder wall.ResultsFurthering this hypothesis, in this experiment, we were successful in introducing syngeneic, healthy SMCs into diabetic bladders. We attempted a method wherein bladder function can be improved in streptozocin-induced diabetes mellitus. Ex vivo–cultured healthy SMCs were introduced into the diabetic bladders of syngeneic Sprague-Dawley rats during the hypercontractile phase after induction of diabetes. Cystometry, metabolic cage evaluation, organ bath studies and histological analyses were performed on the healthy control, the diabetic and the diabetic group transplanted with SMCs.ConclusionsDuring the 2-week follow-up period after transplantation, we noticed an increase in contractile response of the bladder correlating to a decrease in residual urine. Cell survival studies revealed a cell survival rate close to 1.5%.     

Changes in cardiac contractile function and myocardial

Cutaneous burn trauma causes cardiac contraction and relaxation defects, but the mechanism is unclear. Previous studies suggest that burn-related changes in myocyte handling of calcium may play an important role in postburn cardiac dysfunction. With the use of a high dissociation constant (K(d)) calcium indicator 1,2-bis(2-amino-5,6-difluorophenoxy)-ethane-N,N,N',N'-tetraacetic acid (TF-BAPTA) and (19)F NMR spectroscopy, this study examined the correlation between the changes in cytosolic free calcium concentration ([Ca(2+)](i)) and cardiac function after burn trauma. Sprague-Dawley rats were given scald burn (over 40% of the total body surface area) or sham burn. Twenty-four hours later, the hearts were excised and perfused by the Langendorff method with a modified phosphate-free Krebs-Henseleit bicarbonate buffer. Left ventricular (LV) developed pressure (LVDP), calculated from peak systolic LV pressure and LV end-diastolic pressure, was assessed through a catheter attached to an intraventricular balloon. At the same time, (31)P and (19)F NMR spectroscopy was performed before and after TF-BAPTA loading. LVDP measured in hearts from burned rats was <40% than that measured in hearts from sham burn rats (65 +/- 6 vs. 110 +/- 12 mmHg, P < 0.01); [Ca(2+)](i) was increased fourfold in hearts from the burned group compared with that measured in the sham burn group (0.807 +/- 0.192 vs. 3.891 +/- 0.929 microM). Loading TF-BAPTA in hearts transiently decreased LVDP by 15%. Phosphocreatine-to-P(i) ratio decreased, but ATP and intracellular pH remained unchanged by either TF-BAPTA loading or burn trauma. In conclusion, burn trauma impaired cardiac contractility, and this functional defect was paralleled by a significant rise in [Ca(2+)](i) in the heart.     

Myokinase and contractile function of glycerinated muscle fibers

Glycerinated rabbit psoas muscle fibers containing native CPK, ATPase, and myokinase activities were used and isometric contraction and relaxation responses to either ADP or ATP + CP or to ATP alone in the presence and absence of P1, P5-di(adenosine-5'-pentaphosphate), a myokinase inhibitor, were compared. In previous (14) work it was shown that CP generated more efficient and faster contraction and relaxation of glycerinated muscle fibers than ATP. The present work deals with the role of myokinase in the differential response of fibers to CP and ATP. Inhibition of the myokinase activity of these fibers caused slight diminution of the rate of contraction at physiological concentrations of ATP. Uninhibited fibers were not able to reach maximum contraction, because the tension began to drop gradually even in the presence of Ca2+. Addition of Ap5A permitted maximum contraction and the ability to stay at the contracted state. In the case of CP + adenosine nucleotides (ATP or ADP), myokinase activity decreased the rate of tension development which was statistically significant after 5-7 sec of contraction. Thus, a higher tension was obtainable when myokinase was inhibited. At high concentration of adenine nucleotides (greater than 2 mM) and in the absence of Ap5A, not only the maximum tension never was reached, but a spontaneous drop in tension was observed before addition of EGTA, as was seen with ATP alone. Relaxation was faster and more complete in the presence of uninhibited myokinase activity except that the ADP was low (125 mM). These observations provide further evidence for a close functional interaction of these three enzymes in the mechanism of contraction and relaxation, giving further support to the notion of the creatine-phosphocreatine energy shuttle.     

The contractile vacuole and its membrane dynamics

The contractile vacuole (CV) is an osmoregulatory organelle whose mechanisms of function are poorly understood. Immunological studies in the last decade have demonstrated abundant proton-translocating V-type ATPases (V-ATPases) in its membrane that could provide the energy, from proton electrochemical gradients, for moving ions into the CV to be followed by water. This review emphasizes recent work on the contractile vacuole complex (CVC) of Paramecium including (1) CV expulsion, (2) a role for V-ATPases in sequestering fluid, (3) identifying ions in the cytosol and in the CV, (4) in situ electrophysiological parameters of the CVC membrane, and (5) a better understanding of the membrane dynamics of this organelle.     

Cardiac hypertrophy and changes in contractile function of cardiomyocyte

To investigate the cellular mechanisms of pressure-overload cardiac hypertrophy transition to heart failure, we observed time course of changes in morphology and contractile function of cardiomyocytes in transverse abdominal aortic constriction (TAC) rats. Since TAC rats suffered higher stress, body weight had a slower growth rate compared with that of synchronous control rats. Therefore, the left ventricular to body weight ratio produced experimental bias to evaluate the degree of cardiac hypertrophy. Length and width of collagenase-isolated cardiomyocyte were directly measured. Length, width and calculated surface area of cardiomyocyte showed a progressive increase in 8-, 16-, and 20-week TAC rats. The increasing rate of surface area in cardiomyocytes was higher at the middle stage of TAC (from the eighth to sixteenth week). Due to the constraint of fibrosis formation, the increasing rate of surface area in cardiomyocytes was slower at the late stage of TAC (from the sixteenth to twentieth week). The sarcomere length of cardiomyocytes was unchanged, whereas sarcomere numbers were significantly increased in 8-, 16-, and 20-week TAC rats. Shortening amplitude of unloaded contraction in single cardiomyocyte was significantly enhanced in 1-week TAC rats, but not altered in 8-week TAC rats compared with that in the synchronous control rats. On the contrary, unloaded shortening amplitude of single cardiomyocyte was significantly reduced in 16- and 20-week TAC rats. The above results suggest that the reduced shortening amplitude may be associated with intrinsic molecular alterations in hypertrophied cardiomyocytes.     

The tachykinin NK-2 receptor antagonist SR48968 does not block noncholinergic contractions in unstable human bladder

Concentration-response curves to acetylcholine, and responses to electrical field stimulation (EFS) were compared in detrusor muscle strips, from control patients and those with idiopathic detrusor instability (IDI). Responses were similar in both groups. However, atropine abolished responses to EFS in 80% of control but only 33% of IDI patients (P>0.05), with the residual atropine-resistant response in most IDI patients abolished by tetrodotoxin. The post-atropine residual response was unaffected by the tachykinin NK-2 receptor antagonist SR48968. Despite the known existence of NK-2 receptors in the human detrusor, there was no evidence for tachykinin contribution to EFS-induced contractions.     

Superoxide dismutase C affects Dictyostelium contractile vacuole biogenesis and function

Dictyostelium cells cope with hypo-osmotic stress with a contractile vacuole (CV) system, which consists of one or two vacuoles that cyclically charge and discharge. Uniquely, a F-Actin remodeling dependent minimal mixing of the CV membrane components with the target plasmalemma during the fusion and the dischargement warrants the integrity of the CV bladder for an efficient next CV cycle. The effect of hypo-osmotic stress on F-Actin remodeling activity, however, is currently not well understood. Dictyostelium cells increase the level of intracellular superoxide level in response to hypo-osmotic stress, which in turn activates redox-sensitive Ras proteins, but not Akt, which is one of the Ras downstream targets and a major regulator of F-Actin remodeling. However, Akt is not insulated from the active Ras in cells lacking Superoxide dismutase C (SodC). We report here that sodC^- cells were compromised in the CV structure and function and the attenuation of Ras/PI3K/Akt signaling in several independent means significantly improved the compromised CV structure but not the function. Interestingly, when sodC^- cells were treated with 5-(N,N-Dimethyl) amiloride hydrochloride (EIPA), an inhibitor of sodium proton exchanger (NHE), both the structure and the function of the CV improved. Thus, a proper CV biogenesis in sodC^- cells was insufficient to restore their CV function, which in turn indicates the presence of an additional target for SodC and EIPA that modulates CV function.     

Lymphatic muscle: a review of contractile function

A recent surge in lymphangiogenesis research has led to a greater understanding of lymphatic endothelial cell biology. However, a general understanding of lymphatic muscle cell biology lags far behind its endothelial counterpart. Lymphatics at the level of the collecting vessels and higher contain muscular walls capable of both tonic and phasic contractions, which both generate and regulate lymph flow. Because lymphatic contraction is crucial to lymphatic function, a solid understanding of lymphatic muscle development and function is necessary to understand lymphatic biology. This review summarizes the current body of lymphatic muscle research and addresses important questions that are currently unanswered.     

Longitudinal strain quantitates regional right ventricular contractile function

The assessment of contractile function of the right ventricle (RV) is an important clinical issue, but this remains difficult because of its complex anatomy and structure. We thought to investigate whether new Doppler-derived myocardial deformation indexes may quantify regional contractile RV function during varying loading conditions. In nine pigs, ultrasonic crystals were inserted longitudinally in the RV inflow and outflow tracts to assess regional contractile function. The same RV segments and the interventricular septum were imaged using apical echocardiographic views. Regional function was assessed using two parameters: 1) systolic strain (SS), representing the relative magnitude of segmental systolic shortening; and 2) its temporal derivative, peak systolic strain rate (SR), i.e., the maximal velocity of segmental shortening. Data were acquired at baseline and during partial pulmonary artery constriction (PAC) and inferior vena cava occlusion (IVCO). SS decreased significantly after PAC and IVCO in both the inflow and outflow tracts but only during IVCO in the septum. SR was less sensitive to loading variations in all segments. A significant correlation was found between SS values derived from sonomicrometry and myocardial Doppler in RV segments (r = 0.84, P < 0.001). Thus regional strain and SR provide complementary information on the heterogeneous RV contractile function and can be accurately and noninvasively quantified using Doppler myocardial imaging.     

Inhibition of contractile vacuole function by brefeldin A

Brefeldin A (BFA) causes a block in the secretory system of eukaryotic cells. In the scaly green flagellate Scherffelia dubia, BFA also interfered with the function of the contractile vacuoles (CVs). The CV is an osmoregulatory organelle which periodically expels fluid from the cell in many freshwater protists. Fusion of the CV membrane with the plasma membrane is apparently blocked by BFA in S. dubia. The two CVs of S. dubia swell and finally form large central vacuoles (LCVs). BFA-induced formation of LCVs depends on V-ATPase activity, and can be reversed by hypertonic media, suggesting that water accumulation in the LCVs is driven by osmosis. We suggest that the BFA-induced formation of LCVs represents a prolonged diastole phase. A normal diastole phase takes about 20 s and is difficult to investigate. Therefore, BFA-induced formation of LCVs in S. dubia represents a unique model system to investigate the diastole phase of the CV cycle.