Ca2+ sensitization of smooth muscle contractility induced by ruthenium red

Transient receptor potential ion-channel subfamily V member 4: a potential target for cancer treatment

The transient receptor potential ion-channel superfamily consists of nonselective cation channels located mostly on the plasma membranes of numerous animal cell types, which are closely related to sensory information transmission (e.g., vision, pain, and temperature perception), as well as regulation of intracellular Ca2+ balance and physiological activities of growth and development. Transient receptor potential ion channel subfamily V (TRPV) is one of the largest and most diverse subfamilies, including TRPV1-TRPV6 involved in the regulation of a variety of cellular functions. TRPV4 can be activated by various physical and chemical stimuli, such as heat, mechanical force, and phorbol ester derivatives participating in the maintenance of normal cellular functions. In recent years, the roles of TRPV4 in cell proliferation, differentiation, apoptosis, and migration have been extensively studied. Its abnormal expression has also been closely related to the onset and progression of multiple tumors, so TRPV4 may be a target for cancer diagnosis and treatment. In this review, we focused on the latest studies concerning the role of TRPV4 in tumorigenesis and the therapeutic potential. As evidenced by the effects on cancerogenesis, TRPV4 is a potential target for anticancer therapy.

Transepithelial transport of zinc and L-histidine across perfused intestine of American lobster, Homarus americanus

The intestine of the American lobster, Homarus americanus, was isolated and perfused in vitro with a physiological saline, based on the ion composition of the blood, to characterize the mechanisms responsible for transmural transport of zinc and how the amino acid, L-histidine, affects the net movement of the metal across the tissue. Previous studies with this preparation, focusing on the characteristics of unidirectional mucosa to serosa (M to S) fluxes of (65)Zn(2+) and (3)H-L-histidine, indicated the presence of a brush border co-transport process responsible for simultaneously transferring the metal and amino acid across this tissue as an apparent bis-complex (Zn-[His](2)) using a PEPT-1-like dipeptide carrier mechanism. In addition, both zinc and L-histidine were also transferred toward the blood by separate transporters that were independent of the other substrate. The focus of the present study was to characterize the serosa to mucosa (S to M) flux of (65)Zn(2+) under a variety of conditions, and use these values in conjunction with those from the previous study, to assess the direction and magnitude of net metal movement across the tissue. Transmural S to M transport of (65)Zn(2+) was markedly reduced with the addition of the serosal inhibitors ouabain (32%), excess K(+) (25%), excess Ca(2+) (30%), Cu(2+) (38%), nifedipine (21%), and vanadate (53%). In contrast, this flux was markedly stimulated with the serosal addition of ATP (24%) and excess Na(+) (28%). These results suggest that S to M fluxes of zinc occurred by the combination of the basolateral Na/Ca exchanger (NCX), where zinc replaced calcium, and a basolateral nifedipine-sensitive calcium channel. Transmural M to S (65)Zn(2+) fluxes (5-100 microM) were threefold greater than S to M metal transport, and the addition of luminal L-histidine doubled the net M to S zinc flux over its rate in the absence of the amino acid. The results of this paper and those in its predecessor indicate that zinc transport by the lobster intestine is absorptive and significantly enhanced by luminal amino acids.

Physiological characterization of 45Ca2+ and 65Zn2+ transport by lobster hepatopancreatic endoplasmic reticulum

The crustacean hepatopancreas is an epithelial-lined, multifunctional organ that, among other activities, regulates the flow of calcium into and out of the animal's body throughout the life cycle. Transepithelial calcium flow across this epithelial cell layer occurs by the combination of calcium channels and cation exchangers at the apical pole of the cell and by an ATP-dependent, calcium ATPase in conjunction with a calcium channel and an Na+/Ca2+ antiporter in the basolateral cell region. The roles of intracellular organelles such as mitochondria, lysosomes, and endoplasmic reticulum (ER) in transepithelial calcium transport or in transient calcium sequestration are unclear, but may be involved in transferring cytosolic calcium from one cell pole to the other. The ER membrane has a complement of ATP-dependent calcium ATPases (SERCA) and calcium channels that regulate the uptake and possible transfer of calcium through this organelle during periods of intense calcium fluxes across the epithelium as a whole. This investigation characterized the mechanisms of calcium transport by lobster hepatopancreatic ER vesicles and the effects of drugs and heavy metals on them. Kinetic constants for 45Ca2+ influx under control conditions were K(n) (m)=10.38+/-1.01 microM, J(max)=14.75+/-1.27 pmol/mg protein x sec, and n=2.53+/-0.46. The Hill coefficient for 45Ca2+ influx under control conditions, approximating 2, suggests that approximately two calcium ions were transported for each transport cycle in the absence of ATP or the inhibitors. Addition of 1 mM ATP to the incubation medium significantly (P<0.01) elevated the rate of 45Ca2+ influx at all calcium activities used and retained the sigmoidal nature of the transport relationship. The kinetic constants for 45Ca2+ influx in the presence of 1 mM ATP were K(n) (m)=12.76+/-0.91 microM, J(max)=25.46+/-1.45 pmol/mg protein x sec, and n=1.95+/-0.15. Kinetic analyses of ER 65Zn2+ influx resulted in a sigmoidal relationship between transport rate and zinc activity under control conditions (K(n) (m)=38.63+/-0.52 microM, J(max)=19.35+/-0.17 pmol/mg protein x sec, n=1.81+/-0.03). The Addition of 1 mM ATP enhanced 65Zn2+ influx at each zinc activity, but maintained the overall sigmoidal nature of the kinetic relationship. The kinetic constants for zinc influx in the presence of 1 mM ATP were K(n) (m)=34.59+/-2.31 microM, J(max)=26.09+/-1.17 pmol/mg protein x sec, and n=1.96+/-0.17. Both sigmoidal and ATP-dependent calcium and zinc influxes by ER vesicles were reduced in the presence of thapsigargin and vanadate. This investigation found that lobster hepatopancreatic ER exhibited a thapsigargin- and vanadate-inhibited, SERCA-like, calcium ATPase. This transporter displayed cooperative calcium transport kinetics (Hill coefficient, n approximately 2.0) and was inhibited by the heavy metals zinc and copper, suggesting that the metals may reduce the binding and transport of calcium when they are present in the cytosol.

Pharmacological modulation of sarcoplasmic reticulum function in smooth muscle

The sarco/endoplasmic reticulum (SR/ER) is the primary storage and release site of intracellular calcium (Ca2+) in many excitable cells. The SR is a tubular network, which in smooth muscle (SM) cells distributes close to cellular periphery (superficial SR) and in deeper aspects of the cell (deep SR). Recent attention has focused on the regulation of cell function by the superficial SR, which can act as a buffer and also as a regulator of membrane channels and transporters. Ca2+ is released from the SR via two types of ionic channels [ryanodine- and inositol 1,4,5-trisphosphate-gated], whereas accumulation from thecytoplasm occurs exclusively by an energy-dependent sarco-endoplasmic reticulum Ca2+-ATPase pump (SERCA). Within the SR, Ca2+ is bound to various storage proteins. Emerging evidence also suggests that the perinuclear portion of the SR may play an important role in nuclear transcription. In this review, we detail the pharmacology of agents that alter the functions of Ca2+ release channels and of SERCA. We describe their use and selectivity and indicate the concentrations used in investigating various SM preparations. Important aspects of cell regulation and excitation-contractile activity coupling in SM have been uncovered through the use of such activators and inhibitors of processes that determine SR function. Likewise, they were instrumental in the recent finding of an interaction of the SR with other cellular organelles such as mitochondria. Thus, an appreciation of the pharmacology and selectivity of agents that interfere with SR function in SM has greatly assisted in unveiling the multifaceted nature of the SR.

65Zn2+ transport by lobster hepato-pancreatic baso-lateral membrane vesicles

The lobster (Homarus americanus) hepato-pancreatic epithelial baso-lateral cell membrane possesses three transport proteins that transfer calcium between the cytoplasm and hemolymph: an ATP-dependent calcium ATPase, a sodium-calcium exchanger, and a verapamil-sensitive cation channel. We used standard centrifugation methods to prepare purified hepato-pancreatic baso-lateral membrane vesicles and a rapid filtration procedure to investigate whether (65)Zn(2+) transfer across this epithelial cell border occurs by any of these previously described transporters for calcium. Baso-lateral membrane vesicles were osmotically reactive and exhibited a time course of uptake that was linear for 10-15 s and approached equilibrium by 120 s. In the absence of sodium, (65)Zn(2+) influx was a hyperbolic function of external zinc concentration and followed the Michaelis-Menten equation for carrier transport. This carrier transport was stimulated by the addition of 150 microM ATP (increase in K(m) and J(max)) and inhibited by the simultaneous presence of 150 micromol l(-1) ATP+250 micromol l(-1) vanadate (decrease in both K(m) and J(max)). In the absence of ATP, (65)Zn(2+) influx was a sigmoidal function of preloaded vesicular sodium concentration (0, 5, 10, 20, 30, 45, and 75 mmol l(-1)) and exhibited a Hill Coefficient of 4.03+/-1.14, consistent with the exchange of 3 Na(+)/1Zn(2+). Using Dixon analysis, calcium was shown to be a competitive inhibitor of baso-lateral membrane vesicle (65)Zn(2+) influx by both the ATP-dependent (K(i)=205 nmol l(-1) Ca(2+)) and sodium-dependent (K(i)=2.47 micromol l(-1) Ca(2+)) transport processes. These results suggest that zinc transport across the lobster hepato-pancreatic baso-lateral membrane largely occurred by the ATP-dependent calcium ATPase and sodium-calcium exchanger carrier proteins.

Hypoxia enhances a cGMP-independent nitric oxide relaxing mechanism in pulmonary arteries

Nitric oxide (NO) donors generally relax vascular preparations through cGMP-mediated mechanisms. Relaxation of endothelium-denuded bovine pulmonary arteries (BPA) and coronary arteries to the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) is almost eliminated by inhibition of soluble guanylate cyclase activation with 10 microM 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), whereas only a modest inhibition of relaxation is observed under hypoxia (PO2 = 8-10 Torr). This effect of hypoxia is independent of the contractile agent used and is also observed with NO gas. ODQ eliminated SNAP-induced increases in cGMP under hypoxia in BPA. cGMP-independent relaxation of BPA to SNAP was not attenuated by inhibition of K+ channels (10 mM tetraethylammonium), myosin light chain phosphatase (0.5 microM microcystin-LR), or adenylate cyclase (4 microM 2',5'-dideoxyadenosine). SNAP relaxed BPA contracted with serotonin under Ca2+-free conditions in the presence of hypoxia and ODQ, and contraction to Ca2+ readdition was also attenuated. The sarcoplasmic reticulum Ca2+-reuptake inhibitor cyclopiazonic acid (0.2 mM) attenuated SNAP-mediated relaxation of BPA in the presence of ODQ. Thus hypoxic conditions appear to promote a cGMP-independent relaxation of BPA to NO by enhancing sarcoplasmic reticulum Ca2+ reuptake.

Stimulatory effect of centrally injected capsaicin, an agonist of vanilloid receptors, on gastric acid secretion in rats

Capsaicin, the main pungent ingredient in chilli peppers, acts through specific vanilloid receptors on sensory neurons. The vanilloid receptors have been localized in the brain. We describe here a stimulatory effect of centrally injected capsaicin on gastric acid secretion in urethane-anesthetized rats. Injection of capsaicin (10-30 nmol per rat) into the lateral cerebroventricle markedly stimulated the secretion. Injection of capsazepine (30 nmol) or ruthenium red (30 nmol), antagonists for vanilloid receptors, into the lateral cerebroventricle inhibited the secretion induced by capsaicin, although these antagonists alone significantly stimulated the secretion. Injection of capsaicin into the fourth cerebroventricle also stimulated gastric acid secretion. The effects of centrally injected capsaicin into the lateral and fourth cerebroventricle were mediated via the vagus cholinergic nerve, because the effects were abolished by bilateral vagotomy at the cervical level. The present findings showed that central injection of capsaicin stimulated gastric acid secretion, via vanilloid receptors in the central nervous system (CNS), and through vagus nerve mechanisms in the perfused stomach of urethane-anesthetized rats.

Calcium-mediated activation of pyruvate dehydrogenase in severely injured postischemic myocardium

Indirect evidence suggests that activity of pyruvate dehydrogenase (PDH) influences recovery of the myocardium after transient ischemia. The present study examined the relationship between postischemic injury and activity of PDH and the role of mitochondrial calcium uptake for observed changes in PDH activity. Isovolumically beating isolated rat hearts perfused with erythrocyte-enriched buffer containing glucose, palmitate, and insulin were submitted to either 20 or 35 min of no-flow ischemia. After 20 min of no-flow ischemia, hearts exhibited complete recovery of developed left ventricular pressure (DLVP). The proportion of myocardial PDH in the active state was modestly increased to 38% (compared with 13% in control hearts) without a change in glucose oxidation. In contrast, in hearts subjected to 35 min of no-flow ischemia (which exhibited poor recovery of DLVP), there was marked stimulation of glucose oxidation (+460%; P < 0.01) and pronounced increase in the active fraction of PDH to 72% (P < 0.01). Glycolytic flux was not significantly altered. Ruthenium red (6 microM) completely abolished the activation of PDH and the increase in glucose oxidation. The results indicate that variable stimulation of glucose oxidation during reperfusion is related to different degrees of activation of PDH, which depends on the severity of the ischemic injury. Activation of PDH seems to be mediated by myocardial calcium uptake.

Blockade by ruthenium red of tissue factor-initiated coagulation

The ability of ruthenium red (RuR) to inhibit tissue factor (TF)-initiated blood coagulation was demonstrated at the protein and cellular levels as well as in human plasma. In a single-stage clotting assay, RuR concentration-dependently inhibited rabbit brain thromboplastin (rbTF)-induced coagulation and offset bacterial endotoxin (LPS)-induced monocytic TF (mTF) hypercoagulation; the IC(50)s were estimated at 7.5 and 12.3 microM, respectively. A 15-min preincubation of RuR with rbTF or monocyte suspension resulted in the pronounced inhibition with a significantly lowered IC(50) at 1.8 or 7.7 microM for rbTF or mTF procoagulation, respectively. The differences in IC(50)s between rbTF and mTF without or with the preincubation indicated that TF was a primary target for RuR action. The effect of RuR on the physiological function of TF in FVII activation was demonstrated by the proteolytic cleavage of FVII zymogen to its active forms of serine protease on Western blotting analyses. RuR readily blocked TF-catalyzed FVII activation (diminished FVIIa formation), thus down regulating the initiation of blood coagulation. Inclusion of RuR into human plasma samples in vitro significantly prolonged prothrombin time, indicating the depressed coagulation. FVII activity was inhibited by 30 - 60% depending on the dose; as a result, FX activity also decreased. However, RuR showed no effect on thrombin time. Thus, RuR inhibited FVII activation to block the initiation of coagulation.

Inhibition of smooth-muscle myosin-light-chain phosphatase by Ruthenium Red

Ruthenium Red (RuR) is widely used as an inhibitor of ryanodine receptor Ca(2+) release channels, but has additional effects such as the induction of Ca(2+) sensitization of contraction of permeabilized smooth muscles. To address the mechanism underlying this process, we examined the effects of RuR on contractility in permeabilized guinea-pig ileum and on the activity of myosin-light-chain phosphatase (MP). RuR increased the force at submaximal [Ca(2+)] (pCa 6.3) approx. 4-fold. This effect was not observed after thiophosphorylation of MP. RuR also seemed capable of preventing the thiophosphorylation of MP, suggesting a direct interaction of RuR with MP. Consistent with this possibility, smooth-muscle MP was inhibited by RuR in a concentration-dependent manner (IC(50) 23 microM). Exogenous calmodulin significantly increased RuR-induced contraction at pCa 6.3 but had little effect on contraction induced by microcystin at this [Ca(2+)]. Ca(2+)-independent contraction was induced by RuR (EC(50) 843 microM) and by microcystin (EC(50) 59 nM) but the maximal force induced by RuR was smaller than that induced by microcystin. The addition of 300 microM RuR enhanced the contraction induced by 30 nM microcystin but markedly decreased that induced by 1 microM microcystin. Such a dual action of RuR on microcystin-induced effects was not observed in experiments using purified MP. We conclude that the RuR-induced Ca(2+) sensitization of smooth-muscle contraction is due to the direct inhibition of MP by RuR.