scholarly journals Extracellular ATP-induced acidification leads to cytosolic calcium transient rise in single rat cardiac myocytes

1991 ◽  
Vol 274 (1) ◽  
pp. 55-62 ◽  
Author(s):  
M Pucéat ◽  
O Clément ◽  
F Scamps ◽  
G Vassort
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Myocytes ◽  
Membrane Conductance ◽  
Calcium Transient ◽  
Cytosolic Calcium ◽  
Extracellular Atp ◽  
Experimental Conditions ◽  
Extracellular Medium ◽  
Voltage Dependent ◽  
Ca2 Channels

The origin of the increase in cytosolic free Ca2+ concentration ([Ca2+]i) induced by extracellular ATP was investigated in single isolated cardiac myocytes loaded with indo-1. The nucleotide added at a concentration of 10 microM triggers a few Ca2+ spikes, followed by a cluster of Ca2+ oscillations, increasing [Ca2+]i to around 200 nM from a basal value of 70 nM. Neither caffeine nor ryanodine affects the magnitude of the Ca2+ transient, but both shorten it by preventing the Ca2+ oscillations. This indicates that the latter must be related to the release of Ca2+ from the sarcoplasmic reticulum. Since ATP also induces cell depolarization (as shown by experiments using the potential sensitive dye bis-oxonol), the initial Ca2+ spikes were attributed to the opening of voltage-dependent Ca2+ channels. A small Ca2+ transient still remains under experimental conditions designed to prevent Ca2+ influx from external medium (low-Ca2+ high-Mg2+ medium containing La3+) and after depletion of the sarcoplasmic-reticulum Ca2+ load with caffeine. Under these conditions, when this Ca2+ transient was buffered by 1,2-bis-(O-aminophenoxy)ethane-NNN′N′-tetra-acetic acid, ATP was unable to trigger the initial Ca2+ spikes. These results indicate that ATP mobilizes Ca2+ ions from an intracellular pool other than the sarcoplasmic reticulum and that this Ca2+ release is responsible for the depolarization. The effects of ATP on [Ca2+]i share the same characteristics as the acidification simultaneously induced by the nucleotide (as shown by experiments using the pH-sensitive probe snarf-1). These ionic variations are highly specific to ATP and its hydrolysis-resistant analogues. They both require the presence of Mg2+ and Cl- ions in the extracellular medium, and they are prevented by pretreatment of the cells with 4,4′-di-isothiocyanostilbene or probenecid. These results suggest that: (1) the ATP-induced acidification leads to displacement of Ca2+ ions from or close to the internal face of sarcolemma; (2) the Ca2+ ions activate a non-specific membrane conductance responsible for the depolarization of the cells; (3) the depolarization leads to a Ca2+ influx, owing to the opening of the voltage-dependent Ca2+ channels; (4) this increase in Ca2+ triggers the release of Ca2+ from the sarcoplasmic reticulum, which is facilitated by the increase in inositol trisphosphate following P2-purinergic stimulation.

Acute hypoxia increases cytosolic calcium in cultured pulmonary arterial myocytes

1993 ◽  
Vol 264 (3) ◽  
pp. L323-L328 ◽  
Author(s):  
C. G. Salvaterra ◽  
W. F. Goldman
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Acute Hypoxia ◽  
Cytosolic Calcium ◽  
Pulmonary Arterial ◽  
Pulmonary Arterial Smooth Muscle ◽  
Early Rise ◽  
Ca2 Channels ◽  
State Increase

The effects of hypoxia on the cytosolic Ca2+ concentration, [Ca2+]i, were characterized in cultured pulmonary arterial smooth muscle (PASM) cells. Reducing O2 tension (PO2) from 150 to < 25 Torr induced a reversible 100-200% increase in [Ca2+]i that was characterized by two components: an early rise in [Ca2+]i that was dependent on the rate, as well as the magnitude, of decline in PO2 and a later, steady-state increase that was independent of the rate at which PO2 changed. Caffeine lowered [Ca2+]i during normoxia and blocked the early component of the response to hypoxia, whereas the steady-state hypoxic response was only partially inhibited. Like hypoxia, thapsigargin (TG) elevated [Ca2+]i, and there was no additional hypoxia-induced elevation in [Ca2+]i at any time after exposure to TG. At steady state, the hypoxic responses were completely reversed by removal of extracellular Ca2+, whereas, on average, verapamil and nifedipine attenuated the hypoxia-induced increases in [Ca2+]i by only 44 and 35%, respectively. These results suggest that hypoxia-induced elevation of [Ca2+]i in PASM cells consists of an early release of Ca2+ from the sarcoplasmic reticulum and a later influx of extracellular Ca2+, in part, through nifedipine- and verapamil-insensitive Ca2+ channels. The results are consistent with the idea that hypoxia and thapsigargin may share common mechanisms for tonically increasing [Ca2+]i.

scholarly journals Characteristic of the vasorlaxant action of the talatisamine alkaloid and its derivatives

2021 ◽  
Vol 4 (2) ◽  
pp. 01-05
Author(s):  
Mirzayeva Yu.T.
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Channel Blocker ◽  
Aortic Ring ◽  
Diterpenoid Alkaloids ◽  
Relaxant Effect ◽  
Ring Contraction ◽  
Voltage Dependent ◽  
Ca2 Channels ◽  
Isolated Rat

The aim of our research is to study the effect relaxant action of diterpenoid alkaloids talatisamine, 14-O-benzoylthalatisamine and 14-O-acetylthalatisamine was studied using isolated rat aortic rings. Alkaloids significantly and dose-dependently inhibited contraction of the aortic rings caused by high KCl content. At the same time, under these conditions, alkaloids significantly reduced Ca2+-induced contraction of the aortic rings. The relaxing effects of alkaloids are significantly suppressed by verapamil, a potent potentiometer-dependent Ca2+ channel blocker. The alkaloids also significantly reduced norepinephrine-induced aortic ring contraction in normal as well as Ca2+ free Krebs solutions. The data obtained indicate that talatisamine, 14-benzoylthalatisamine and 14-O-acetylthalatisamine exhibit a pronounced relaxant effect in almost the same way in the case of contraction induced by a high content of KCl and norepinephrine. The mechanism of the relaxant action of alkaloids is probably complex and may include suppression of Ca2+influx through voltage-dependent and receptor-driven Ca2+ channels, as well as inhibition of Ca2+transport in the sarcoplasmic reticulum.

scholarly journals L-type Ca2+ channels in the heart: Structure and regulation

Medicina ◽  
2008 ◽  
Vol 44 (7) ◽  
pp. 491 ◽  
Author(s):  
Rimantas Treinys ◽  
Jonas Jurevičius
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Myocytes ◽  
Extracellular Space ◽  
Heart Diseases ◽  
Life Quality ◽  
Cardiac Cells ◽  
Cell Cytoplasm ◽  
Regulation Mechanisms ◽  
Important System ◽  
Ca2 Channels

This review analyzes the structure and regulation mechanisms of voltagedependent L-type Ca2+ channel in the heart. L-type Ca2+ channels in the heart are composed of four different polypeptide subunits, and the pore-forming subunit a1 is the most important part of the channel. In cardiac myocytes, Ca2+ enter cell cytoplasm from extracellular space mainly through L-type Ca2+ channels; these channels are very important system in heart Ca2+ uptake regulation. L-type Ca2+ channels are responsible for the activation of sarcoplasmic reticulum Ca2+ channels (RyR2) and force of muscle contraction generation in heart; hence, activity of the heart depends on L-type Ca2+ channels. Phosphorylation of channel-forming subunits by different kinases is one of the most important ways to change the activity of L-type Ca2+ channel. Additionally, the activity of L-type Ca2+ channels depends on Ca2+ concentration in cytoplasm. Ca2+ current in cardiac cells can facilitate, and this process is regulated by phosphorylation of L-type Ca2+ channels and intracellular Ca2+ concentration. Disturbances in cellular Ca2+ transport and regulation of L-type Ca2+ channels are directly related to heart diseases, life quality, and life span.

scholarly journals Modification of a voltage-gated K+ channel from sarcoplasmic reticulum by a pronase-derived specific endopeptidase.

1979 ◽  
Vol 74 (4) ◽  
pp. 457-478 ◽  
Author(s):  
C Miller ◽  
R L Rosenberg
Keyword(s):  
Free Energy ◽  
Sarcoplasmic Reticulum ◽  
Single Channel ◽  
Membrane Conductance ◽  
Phospholipid Bilayer ◽  
K Channel ◽  
Gating Charge ◽  
Voltage Dependent ◽  
Selective Membrane ◽  
Conformational Model

AK+ -selective membrane conductance channel from rabbit sarcoplasmic reticulum (SR) is studied in an artificial planar phospholipid bilayer. Membranes containing many such channels display voltage-dependent conductance, which is well described by a two-state conformational equilibrium with a free energy term linearly dependent on applied voltage. Pronase-derived alkaline proteinase b (APb), when added to the side of the membrane opposite to the SR vesicles (trans side), reduces the voltage dependence of the K+ conductance. Single-channel fluctuation experiments show that after APb treatment, the channel is still able to undergo transitions between its open and closed states, but that the probability of forming the open state is only slightly voltage-dependent. In terms of the conformational model, the enzyme's primary effect is to reduce the effective gating charge of the opening process by over 80%; a second effect of APb is to reduce the internal free energy of opening from +1.2 to +0.4 kcal/mol. The kinetics of APb action are strongly voltage-dependent, so as to indicate that the enzyme can react only with the channel's open state. The results imply that the channel contains a highly charged polypeptide region which moves in the direction perpendicular to the membrane plane when transitions between the open and closed states occur. A lysine or arginine residue in this region becomes exposed to the trans aqueous solution when the channel is in its open conformation.

Modulation of contractility by myocyte-derived arginase in normal and hypertrophied feline myocardium

2006 ◽  
Vol 290 (5) ◽  
pp. H1756-H1762 ◽  
Author(s):  
Albert S. Jung ◽  
Hajime Kubo ◽  
Rachel Wilson ◽  
Steven R. Houser ◽  
Kenneth B. Margulies
Keyword(s):  
Cardiac Myocytes ◽  
Functional Significance ◽  
Pressure Overload ◽  
Calcium Transient ◽  
Cytosolic Calcium ◽  
Left Ventricular ◽  
Cgmp Signaling ◽  
Isolated Cardiac Myocytes ◽  
Normal Inhibition ◽  
Arginase I

l-Arginine, the sole substrate for the nitric oxide (NO) synthase (NOS) enzyme in producing NO, is also a substrate for arginase. We examined normal feline hearts and hearts with compensated left ventricular (LV) hypertrophy (LVH) produced by ascending aorta banding. Using Western blot analysis, we examined the abundance of arginase isozymes in crude homogenates and isolated cardiac myocytes obtained from the LVs of normal and LVH hearts. We examined the functional significance of myocyte arginase via measurement of shortening and intracellular calcium in isolated myocytes in the presence and absence of boronoethyl chloride (BEC), a specific pharmacological inhibitor of arginase. Both arginase I and II were detected in crude myocardial homogenates, but only arginase I was present in isolated cardiac myocytes. Arginase I was downregulated in LVH compared with normal. Inhibition of arginase with BEC reduced fractional shortening, maximal rate of shortening (+d L/d t) and relengthening (−d L/d t), and the peak of the free cytosolic calcium transient in normal myocytes but did not affect these parameters in LVH myocytes. These negative inotropic actions of arginase inhibition were associated with increases in cGMP generation. These studies indicate that only arginase I is present in cardiac myocytes where it tends to limit NO and cGMP production with the effect of supporting basal contractility. In experimental LVH induced by pressure overload, our studies demonstrate reduced arginase I expression and reduced functional significance, allowing greater arginine substrate availability for NO/cGMP signaling.

Cardiac Myocytes Differ in mRNA Composition for Sarcoplasmic Reticulum Ca2+Channels and Ca2+Pumpsa

1995 ◽  
Vol 752 (1 Cardiac Growt) ◽  
pp. 141-148 ◽  
Author(s):  
LUISA GORZA ◽  
SILVIA VETTORE ◽  
POMPEO VOLPE ◽  
VINCENZO SORRENTINO ◽  
JANE-LYSE SAMUEL ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Myocytes ◽  
Ca2 Channels

Voltage-dependent effects of isoproterenol on cytosolic Ca concentration in rat heart

1987 ◽  
Vol 252 (4) ◽  
pp. H697-H703 ◽  
Author(s):  
S. S. Sheu ◽  
V. K. Sharma ◽  
M. Korth
Keyword(s):  
Membrane Potential ◽  
Calcium Concentration ◽  
Ventricular Myocytes ◽  
Cytosolic Calcium ◽  
Resting Membrane Potential ◽  
Beta Adrenoceptor ◽  
Adrenoceptor Agonist ◽  
Voltage Dependent ◽  
K Concentration ◽  
Ca2 Channels

The effect of the beta-adrenoceptor agonist, isoproterenol, on cytosolic calcium concentration ([Ca2+]i) was studied with the Ca2+-sensitive fluorescent indicator quin 2 in enzymatically dissociated rat ventricular myocytes. Under conditions in which cells have normal polarized resting membrane potential, isoproterenol (1 microM) produced a decrease in [Ca2+]i. In contrast, in the depolarized cells (by raising extracellular K+ concentration to 50 mM), isoproterenol (1 microM) caused an increase in [Ca2+]i. This isoproterenol-induced increase in [Ca2+]i in depolarized cells could be reversed by prior exposure of the cells to the Ca2+ channel blocker, verapamil (5 microM). The results indicate that isoproterenol can either decrease or increase [Ca2+]i depending on membrane potential. The actual effect of isoproterenol on [Ca2+]i at any given membrane potential probably reflects the relative contributions of isoproterenol-induced stimulation of Ca2+ buffering or effluxing activities (which favor a decrease in [Ca2+]i) and enhancement of Ca2+ influx through voltage-sensitive Ca2+ channels (which favors an increase in [Ca2+]i).

ATP receptor-induced Ca2+ transients in cardiac myocytes: sources of mobilized Ca2+

1989 ◽  
Vol 257 (4) ◽  
pp. C750-C758 ◽  
Author(s):  
M. B. De Young ◽  
A. Scarpa
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ethylene Glycol ◽  
Cardiac Myocytes ◽  
Ventricular Myocytes ◽  
Channel Blockers ◽  
Tetraacetic Acid ◽  
Free Medium ◽  
Fura 2 ◽  
Adult Rat ◽  
Ca2 Channels

Addition of micromolar concentrations of extracellular ATP to adult rat cardiac ventricular myocytes increases cytosolic Ca2+ concentration ([Ca2+]). Experiments were performed on fura-2-loaded myocytes to determine whether the [Ca2+] rise was due to Ca2+ influx, release of Ca2+ from the sarcoplasmic reticulum (SR), or a combination of both. BAY K 8644 and nifedipine affected ATP-induced [Ca2+] transients, indicating involvement of voltage-sensitive Ca2+ channels. Addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or Ca2+ channel blockers significantly reduced cytosolic [Ca2+] changes due to addition of ATP or KCl without depleting Ca2+ stores (shown by ionomycin treatment in a Ca2+-free medium), demonstrating that these responses require Ca2+ influx. Depletion of intracellular Ca2+ stores by caffeine or ryanodine also diminished cytosolic [Ca2+] responses, indicating that a portion of the increased cytosolic [Ca2+] is due to Ca2+ release from SR. Norepinephrine potentiates the ATP-Ca2+ response, and this effect was not inhibited by depletion of intracellular stores. Although the data show that there are two Ca2+ sources in the cytosolic Ca2+ response to ATP, the pattern is also consistent with the hypothesis of Ca2+-induced Ca2+ release from cardiac SR.

Inhibition of voltage-dependent Ca2+influx by extracellular ATP in salivary cells of the leech Haementeria ghilianii

1996 ◽  
Vol 199 (6) ◽  
pp. 1335-1341
Author(s):  
W Wuttke ◽  
T Munsch ◽  
J Deitmer
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Extracellular Atp ◽  
Threshold Concentration ◽  
Resting Membrane Potential ◽  
Voltage Gated ◽  
Voltage Dependent ◽  
K Concentration ◽  
Gamma S ◽  
Ca2 Channels

The effects of extracellular ATP on intracellular free Ca2+ concentration ([Ca2+]i) and depolarization-induced elevations of [Ca2+]i were investigated in salivary cells of the leech Haementeria ghilianii using the fluorescent Ca2+ indicator Fura-2. Simultaneously, the membrane potential was monitored or controlled by voltage-clamp. The cell membrane was depolarized either by transient elevations of the extracellular K+ concentration ([K+]o) to 90 mmol l-1 or by depolarizing steps under voltage-clamp. The resulting transient elevations of [Ca2+]i (Ca2+ transients) could be repeatedly elicited with little variability in amplitude. Ca2+ transients were completely inhibited by 2 mmol l-1 Ni2+ or in Ca2+-free saline. The transients are, therefore, dependent on Ca2+ influx from the external medium through voltage-gated Ca2+ channels. The Ca2+ influx was rapidly and reversibly inhibited by extracellular application of ATP. The effect was dose-dependent with a threshold concentration below 10(-7) mol l-1. A 50 % reduction in the amplitude of Ca2+ transients was obtained by application of 1&shy;2 &micro;mol l-1 ATP or ATP-gamma-S (apparent IC50, 1.6 &micro;mol l-1 ATP) and Ca2+ transients were almost completely inhibited by 30&shy;100 &micro;mol l-1 ATP. Resting [Ca2+]i, the resting membrane potential and membrane potential changes induced by 90 mmol l-1 [K+]o were not affected by ATP. Adenosine (10 &micro;mol l-1) did not affect resting [Ca2+]i, the resting membrane potential or membrane potential changes induced by 90 mmol l-1 [K+]o and had little effect on Ca2+ transients. Suramin, an antagonist of vertebrate P2 receptors, was without effect on the inhibitory actions of ATP. We conclude that activation of a suramin-insensitive purinoceptor by ATP inhibits Ca2+ influx through voltage-gated Ca2+ channels in the salivary cells of Haementeria ghilianii.

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