Cardiac P2X purinergic receptors as a new pathway for increasing Na⁺ entry in cardiac myocytes.

P2X4 receptors (P2X4Rs) are ligand-gated ion channels capable of conducting cations such as Na(+). Endogenous cardiac P2X4R can mediate ATP-activated current in adult murine cardiomyocytes. In the present study, we tested the hypothesis that cardiac P2X receptors can induce Na(+) entry and modulate Na(+) handling.

Treatment of heart failure by a methanocarba derivative of adenosine monophosphate: implication for a role of cardiac purinergic P2X receptors.

Evidence is accumulating to support a potentially important role for purinergic (P2X) receptors in heart failure (HF). We tested the hypothesis that a hydrolysis-resistant nucleotide analog with agonist activity at myocardial P2X receptors (P2XRs) improves the systolic HF phenotype in mouse and dog models. We developed a hydrolysis-resistant adenosine monophosphate derivative, (1'S,2R,3S,4'R,5'S)-4-(6-amino-2-chloro-9H-purin-9-yl)-1-[phosphoryloxymethyl] bicycle[3.

Reversal of cardiac myocyte dysfunction as a unique mechanism of rescue by P2X4 receptors in cardiomyopathy.

Binary cardiac transgenic (Tg) overexpression of P2X(4) receptors (P2X(4)R) improved the survival of the cardiomyopathic calsequestrin (CSQ) mice. Here we studied the mechanism of rescue using binary P2X(4)R/CSQ Tg and CSQ Tg mice as models. Cellular and intact heart properties were determined by simultaneous sarcomere shortening (SS) and Ca(2+) transients in vitro and echocardiography in vivo.

Role of P2X purinergic receptors in the rescue of ischemic heart failure.

Evidence is accumulating to support the presence of P2X purinergic receptors in the heart. However, the biological role of this receptor remains to be defined. The objectives here were to determine the role of cardiac P2X receptors in modulating the progression of post-myocardial infarction ischemic heart failure and to investigate the underlying mechanism.

An estrogen metabolite, 2-methoxyestradiol, disrupts cardiac microtubules and unmasks muscarinic inhibition of calcium current.

Microtubules provide a chemical signaling function as well as structural support for heart cells. Microtubules modulate autonomic signaling in the heart, and their disruption by colchicine unmasks muscarinic inhibition of Ca (ICa) current. In this study, we compare the actions of the estrogen metabolite, 2-methoxyestradiol (2-ME), with those of colchicine on microtubule stability and chemical signal function in guinea pig-isolated ventricular myocytes.

Characterization and mechanism of P2X receptor-mediated increase in cardiac myocyte contractility.

Cardiac P2X purinergic receptors can mediate an increase in myocyte contractility and a potentially important role in the heart. The P2X(4) receptor (P2X(4)R) is an important subunit of native cardiac P2X receptors. With transgenic mice with cardiac-specific overexpression of P2X(4)R (Tg) used as a model, the objectives here were to characterize the P2X receptor-mediated cellular contractile and Ca(2+) transient effects and to determine the mechanism underlying the receptor-induced increase in myocyte contractility.

Extracellular ATP-stimulated current in wild-type and P2X4 receptor transgenic mouse ventricular myocytes: implications for a cardiac physiologic role of P2X4 receptors.

P2X receptors, activated by extracellular ATP, may be important in regulating cardiac function. The objective of the present study was to characterize the electrophysiologic actions of P2X4 receptors in cardiac myocytes and to determine whether they are involved in mediating the effect of extracellular ATP. Membrane currents under voltage clamp were determined in myocytes from both wild-type (WT) and P2X4 receptor-overexpressing transgenic (TG) mice.

[Preliminary studies of the mechanism of carbachol increase contraction in rat ventricular myocytes].

Aim: To study whether the mAchR agonist Carbachol(Cch, nonselective) causes increased contractions and L-type Ca2+ current [L(Ca(L))] in ventricular myocytes and the mechanism of these effects.

Methods: The effect of Cch on the I(Ca(L)) and Na/Ca exchange current (I(Na/Ca) was studied in patch-clamped ventricular myocytes isolated from rat hearts and superfused with Tyrode's solution (35 degrees C, 1.8 mmol/L [Ca2+]o) and stimulated at 0.

Autonomic regulation of calcium and potassium channels is oppositely modulated by microtubules in cardiac myocytes.

We recently showed that colchicine treatment of rat ventricular myocytes increases the L-type Ca2+ current (I(Ca)) and intracellular Ca2+ concentration ([Ca2+](i)) transients and interferes with adrenergic signaling. These actions were ascribed to adenylyl cyclase (AC) stimulation after G(s) activation by alpha,beta-tubulin. Colchicine depolymerizes microtubules into alpha,beta-tubulin dimers.

[The role of L-type Ca2+ current and reverse mode Na+ -Ca2+ exchange in activation of excitation-contraction coupling in guinea-pig ventricular myocytes].

Aim: To study and compare the excitation-contraction coupling triggered by L-type calcium current and by reverse-mode Na/Ca exchange during depolarizing steps in single guinea-pig ventricular myocytes.

Methods: Whole-cell membrane-potential, membrane-current and cell-shortening data were simultaneously acquired during whole-cell voltage clamp protocols. Voltage clamp pulses elicited ICa(L) at + 10 mV, + 50 mV, + 100 mV and evoked contractions in myocytes superfused with Tyrode's solution at 35 degrees C.

On the role of phosphatase in regulation of cardiac L-type calcium current by cyclic GMP.

Does cGMP, via protein kinase G, inhibit cAMP-stimulated Ca(2+) current (I(Ca(L))) in mammalian ventricular myocytes by phosphorylating the calcium channel at a site different from that acted on by cAMP or by dephosphorylating the calcium channel through phosphatase(s)? We tested these possibilities in guinea pig ventricular myocytes superfused with Tyrode's solution (35 degrees C) and dialyzed with adenosine 5'-O-(3-thiotriphosphate) ([ATPgammaS](pip)). ATPgammaS is a kinase substrate but thiophosphorylated proteins are not phosphatase substrates. With 5 mM [ATPgammaS](pip), I(Ca(L)) increased gradually over 20 to 25 min and then rapidly in the presence of 3-isobutyl-1-methylxanthine.

Mechanism for muscarinic inhibition of I(Ca(L)) is determined by the path for elevating cyclic AMP in cardiac myocytes.

Objective: Does carbachol (CCh) require NO/cGMP for inhibition of L-type calcium current (I(Ca(L))) when either adenylyl cyclase activation or phosphodiesterase suppression is used to raise cAMP?

Methods: The effects of the NO donor SIN-1 (3-morpholino-sydnonimine), CCh and atrial natriuretic peptide (ANP) were evaluated when I(Ca(L)) had been stimulated by isoproterenol (ISO) or 3-isobutyl-1-methylxanthine (IBMX) in guinea pig isolated ventricular myocytes (35 degrees C).

Results: Carbachol, SIN-1 or ANP did not affect basal I(Ca(L)); each inhibited IBMX-stimulated I(Ca(L)). Dialyzed (30-100 microM) ODQ (1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one), a soluble guanylyl cyclase (sGC) inactivator, blocked inhibition of IBMX-stimulated I(Ca(L)) by SIN-1 (10 microM) but not by CCh (1-100 microM) or ANP (100 nM).

Carbachol inhibits the L-type Ca2+ current augmented by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid in guinea pig ventricular myocytes: calcium-sensitivity hypothesis for muscarinic inhibition.

The L-type Ca2+ current [I(Ca(L))] increases with time after patch rupture in guinea pig ventricular myocytes dialyzed with pipette solutions containing > or =20 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid ([BAPTA]pip). I(Ca(L)) progressively increases because BAPTA chelates subsarcolemmal Ca2+ to disinhibit cardiac adenylyl cyclase (AC) activity. We studied inhibition by carbachol (CCh) of I(Ca(L)) (22-24 degrees C).

Comparison of L-type calcium channel blockade by nifedipine and/or cadmium in guinea pig ventricular myocytes.

We tested the assumption that nifedipine blocks L-type calcium current [I(Ca(L))] at +10 mV and unmasks Na(+)/Ca(2+) exchange-triggered contractions in guinea pig isolated ventricular myocytes. Voltage-clamp pulses elicited I(Ca(L)) at +10 mV and evoked contractions in myocytes superfused with Tyrode's solution (35 degrees C). Nifedipine blocked I(Ca(L)) with an IC(50) of 0.

Elevated cAMP suppresses muscarinic inhibition of L-type calcium current in guinea pig ventricular myocytes.

We investigated the effect of carbachol (CCh) on L-type Ca2+ current (ICa(L)) enhanced by dialyzed adenosine 3',5'-cyclic monophosphate (cAMP) and/or bath-applied 3-isobutyl-1-methylxanthine (IBMX) in guinea pig isolated ventricular myocytes. At pipette concentrations ([cAMP]pip) from 30 microM to 1 mM, cAMP increased ICa(L) to 25.8 +/- 0.

Inositol-1,4,5-trisphosphate increases contractions but not L-type calcium current in guinea pig ventricular myocytes.

Objective: We studied the effects of intracellularly applied inositol-1,4,5-trisphosphate (InsP3) to test the hypothesis that InsP3 is a messenger for stimulation of L-type calcium current (ICa(L)) and contractions by muscarinic agonists.

Methods: Voltage clamp pulses elicited ICa(L) that evoked contractions recorded with an edge detector in single guinea pig ventricular myocytes superfused with Tyrode's solution (36 degrees C). InsP3 or cyclic AMP (cAMP) was dialyzed into the cell at selected times via the patch electrode.

Lack of effect of McN-A-343 on membrane current and contraction in guinea pig ventricular myocytes.

We asked whether agonist occupancy of M(1) muscarinic receptor (mAChR) causes increased L-type Ca(2+) [I(Ca(L))] and contractions in ventricular myocytes. Voltage-clamp pulses evoked I(Ca(L)) in guinea pig ventricular myocytes superfused with Tyrode's solution (22-24 degrees C). The mAChR agonists carbachol (Cch, nonselective), McN-A-343 (McN, M(1)-selective), and oxotremorine (Oxo, M(2)-selective) were tested at 0.

Carbachol increases contractions and intracellular Ca++ transients in guinea pig ventricular myocytes.

We tested hypotheses concerning the muscarinic receptor subtype and the involvement of L-type Ca current (ICa) in the stimulation of contractions by carbachol (CCh) in single guinea pig ventricular myocytes. When superfused with Tyrode's solution (36 degrees C, 5.4 mM [Ca++]o) and stimulated at 0.

Carbachol promotes Na+ entry and augments Na/Ca exchange current in guinea pig ventricular myocytes.

The effect of carbachol (CCh) on the Na/Ca exchange current (I(Na/Ca)) was studied in voltage-clamped ventricular myocytes isolated from guinea pig hearts and superfused with Tyrode solution at 35 degrees C. CCh (100 microM) increased outward current during depolarizations (10-200 ms) from -45 mV and tail current amplitude on repolarization; CCh had no effect on the L-type Ca2+ current. Amplitudes of the outward and tail currents declined with increasing duration of the depolarizing clamp pulse.

Mechanisms for depolarization by l-palmitoylcarnitine in single guinea pig ventricular myocytes.

Introduction: The changes of the resting potential (RP) and of the current-voltage (I-V) relationship induced by l-palmitoylcarnitine (l-PC) in the presence of the IKI blocker, cesium, or in the presence of the INa/K blocker, ouabain, were tested in guinea pig ventricular myocytes to ascertain the relative contributions of IKI and INa/K suppression to the membrane depolarization caused by this amphiphile.

Methods And Results: Ramp voltages were applied to myocytes with the whole cell, patch clamp technique. l-PC (10 microM) produced additional membrane depolarization in the presence of either 10 mM Cs+ or 30 microM ouabain.

Biphasic effects of intrapipette cyclic guanosine monophosphate on L-type calcium current and contraction of guinea pig ventricular myocytes.

The effects of intracellular cyclic guanosine monophosphate (cGMP) on L-type calcium current (lCa) and contraction of ventricular myocytes enzymatically isolated from guinea pig hearts were investigated to test the hypothesis that cGMP increases contractions along with ICa in these cells. ICa and contractions, elicited every 15 sec, were recorded simultaneously with a whole-cell voltage-clamp method and a video edge-detector, respectively. Cells were superfused with Tyrode's solution (22 degrees C); the pipette solution contained 120 mM potassium aspartate, 30 mM KCl, 4 mM ATP, 5 mM N-(2-hydroxyethyl)piperazine-N-(2-ethanesulfonic acid), 0.

Regulation of InsP3-induced contractions by myoplasmic calcium in permeabilized atrial muscle.

Objective: We studied the effect of calcium on inositol 1,4,5-trisphosphate (InsP3)-induced contractions in saponin-permeabilized chick atrial muscle (80-100 microns in diameter). Calcium has been proposed to modulate InsP3-induced response and InsP3 binding in other tissue.

Methods: A transient increase in tension was used to detect the release of calcium in this multicellular preparation.

Na+ current and Ca2+ release from the sarcoplasmic reticulum during action potentials in guinea-pig ventricular myocytes.

1. Ca2+ release from the sarcoplasmic reticulum (SR) was examined in enzymatically isolated single guinea-pig ventricular myocytes by monitoring [Ca2+]i with fura-2 during whole-cell recording of action potentials at room temperature (23-25 degrees C). Modulation of Ca2+ release by the Na+ current (INa) was studied by manipulating Na+ influx through the Na+ channel.