An Inotropic Action Caused by Muscarinic Receptor Subtype 3 in Canine Cardiac Purkinje Fibers

Objective. The objective of this study was to investigate the inotropic mechanisms and the related muscarinic receptor subtype of acetylcholine (ACh) in canine cardiac Purkinje fibers. Materials and Methods. Isolated Purkinje fiber bundles were used for the measurement of contraction. The receptor subtype was determined using PCR and real-time PCR methods. Results. ACh evoked a biphasic response with a transient negative inotropic effect followed by a positive inotropic effect in a concentration-dependent manner. The biphasic inotropic actions of ACh were inhibited by the pretreatment with atropine. Caffeine inhibited the positive inotropic effect of ACh. ACh increased inositol-1,4,5-trisphosphate content in the Purkinje fibers, which was abolished by atropine. Muscarinic subtypes 2 (M2) and 3 (M3) mRNAs were detected in the canine Purkinje fibers albeit the amount of M3 mRNA was smaller than M2 mRNA. M1 mRNA was not detected. Conclusion. These results suggest that the positive inotropic action of ACh may be mediated by the activation of IP3 receptors through the stimulation of M3 receptors in the canine cardiac Purkinje fibers.

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Fetal canine cardiac Purkinje fibers: electrophysiology and ultrastructure

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1984.246.2.h250 ◽

1984 ◽

Vol 246 (2) ◽

pp. H250-H260

Author(s):

P. Danilo ◽

R. F. Reder ◽

O. Binah ◽

M. J. Legato

Keyword(s):

Action Potential ◽

Fetal Development ◽

Late Gestation ◽

Dependent Manner ◽

Concentration Dependent Manner ◽

Purkinje Fibers ◽

Ultrastructural Studies ◽

Surface Areas ◽

Cardiac Purkinje Fibers ◽

External Potassium

We studied the ontogenesis of the transmembrane action potential and the ultrastructure of fetal canine Purkinje fibers. Fetal hearts were obtained from fetuses just after implantation to end gestation. Using standard microelectrode recording techniques, we found that action potential characteristics varied linearly over this period of development. Maximum diastolic potential (MDP) ranged from -65 to -85 mV; action potential amplitude (AMP) varied from 100 to 120 mV; maximum upstroke velocity (Vmax) increased from 200 to 550 V/s. Action potential duration measured to 50% repolarization (APD50) increased from 15 to 156 ms while duration measured at full repolarization (APD100) similarly increased from 75 to 236 ms. The relationship between external potassium concentration and membrane potential was equivalent across all stages of fetal development. Tetrodotoxin (TTX, 7.7 X 10(-7) to 1.6 X 10(-5) M) caused concentration-dependent decreases in AMP, Vmax, and APD50. Verapamil (1 X 10(-7) to 1 X 10(-5) M) decreased Vmax and APD50 in a concentration-dependent manner. The effects of both TTX and verapamil were statistically equivalent across all stages of fetal development. Ultrastructural studies of fetal Purkinje fibers showed that myocytes at the earliest stages of development (Purkinje fibers were not visually distinct at this time) were arranged as a tightly packed mosaic with a rounded shape, with a large amount of glycogen, small sparse mitochondria, and relatively large nuclei. Mitotic cells were observed frequently. Purkinje fibers when first identified grossly had fewer myofilaments than working myocardial cells and sarcomeres without M lines. By late gestation, intercalated disks appeared with an increase in surface areas; desmosomes occurred more frequently. Myofilaments are organized around Z bands into rudimentary sarcomeres that still lack M lines. These data indicate that, although the fetal canine Purkinje fiber undergoes marked developmental changes in ultrastructure, cellular electrophysiological changes are more subtle. The action potential has a qualitative appearance similar to those of the neonatal or adult fiber. At no time during fetal development could we find slow-response action potentials.

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Hypothermia modifies anesthetic effect on contractile force and Ca2+ transients in cardiac Purkinje fibers

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1994.267.2.h725 ◽

1994 ◽

Vol 267 (2) ◽

pp. H725-H733 ◽

Cited By ~ 2

Author(s):

J. Sprung ◽

D. F. Stowe ◽

J. P. Kampine ◽

Z. J. Bosnjak

Keyword(s):

Positive Inotropic Effect ◽

Mild Hypothermia ◽

Cardiac Contractility ◽

Volatile Anesthetics ◽

Contractile Force ◽

Isometric Tension ◽

Inotropic Effect ◽

Purkinje Fibers ◽

Peak Tension ◽

Cardiac Purkinje Fibers

Mild hypothermia enhances cardiac contractility, and volatile anesthetics depress contractility. Contractile force (tension) and Ca2+ transients were measured in canine Purkinje fibers at 35 and 25 degrees C with and without halothane and isoflurane to examine how anesthetics attenuate the positive inotropic effect of mild hypothermia. Isometric tension and light emitted from the photoprotein aequorin were used to assess contractility and intracellular Ca2+ transients in fibers stimulated at 40–60 pulses/min. At 35 degrees C, each anesthetic depressed peak tension and peak Ca2+ transients and decreased contractile force duration but, for halothane, increased Ca2+ transient duration. Decreases in tension by both anesthetics at 35 degrees C were converted to marked increases in tension at 25 degrees C, whereas Ca2+ transients were little changed. Removal of anesthetics at 25 degrees C greatly increased tension with a small increase in Ca2+ transients that was much lower than that at 35 degrees C. The curve relating peak contractile force as a function of Ca2+ transients at 25 degrees C during stepwise increases in extracellular CaCl2 was shifted steeper and leftward of the curve at 35 degrees C. These studies suggest that the positive inotropic effect of mild hypothermia is due primarily to increased myofibrillar Ca2+ sensitivity and that anesthetics decrease tension during hypothermia by decreasing myofibrillar Ca2+ sensitivity. Reduced influx of transsarcolemmal or sarcoplasmic reticular Ca2+ may also play a role during mild hypothermia.

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WB4101- and CEC-sensitive positive inotropic actions of phenylephrine in rat cardiac muscle

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1994.266.6.h2462 ◽

1994 ◽

Vol 266 (6) ◽

pp. H2462-H2467

Author(s):

A. P. Williamson ◽

E. Seifen ◽

J. P. Lindemann ◽

R. H. Kennedy

Keyword(s):

Papillary Muscle ◽

Left Atrial ◽

Positive Inotropic Effect ◽

Ventricular Myocardium ◽

Isometric Tension ◽

Inotropic Effect ◽

Dependent Manner ◽

Adrenergic Agonists ◽

Response Curves ◽

Concentration Dependent Manner

This study was designed to determine the role of the alpha 1-adrenergic receptor (AR) subtypes in the positive inotropic action of alpha 1-adrenergic agonists in rat myocardium. Isolated left atrial and papillary muscle were suspended in oxygenated Krebs-Henseleit buffer (37 degrees C) containing 3 microM nadolol and paced at 3.3 Hz. Isometric tension was continuously monitored. Cumulative concentration-response curves for phenylephrine (3 x 10(-7) to 3 x 10(-4) M) were obtained in the presence and absence of WB4101 (4 and 10 nM) and with and without treatment with chloroethylclonidine (CEC; 10, 100, and 300 microM). WB4101 antagonized the effect of phenylephrine in both tissues, increasing half-maximal effective concentration (EC50) values in a concentration-dependent manner. CEC pretreatment also increased EC50 values in both tissues, and 300 microM CEC reduced the maximal positive inotropic effect of phenylephrine by approximately 48 and 38% in left atrial and papillary muscle, respectively. CEC alone elicited significant increases in contractile force that were not readily reversible. These data suggest that the positive inotropic effect of alpha 1-adrenergic agonists in rat atrial and ventricular myocardium results from stimulation of both WB4101- and CEC-sensitive alpha 1-ARs.

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Cholinergic stimulation modulates negative inotropic effect of cocaine on ferret ventricular myocardium

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1996.270.2.h678 ◽

1996 ◽

Vol 270 (2) ◽

pp. H678-H684

Author(s):

L. Miao ◽

Z. Qiu ◽

J. P. Morgan

Keyword(s):

Response Curve ◽

Negative Inotropic Effect ◽

Ventricular Myocardium ◽

Inotropic Effect ◽

Dependent Manner ◽

Cholinergic Stimulation ◽

Concentration Dependent Manner ◽

Cell Shortening ◽

Inotropic State ◽

Concentration Response Curve

We tested the hypothesis that the negative inotropic effect (NIE) of cocaine is mediated, at least in part, by cholinergic stimulation and can be correlated with the degree of adenosine 3',5'-cyclic monophosphate (cAMP) dependency of the inotropic state. Cardiac myocytes were isolated from left ventricles of ferrets and loaded with the fluorescent Ca2+ indicator indo 1. Cells were placed in physiological solution containing 2.0 mM Ca2+ and stimulated at 0.5 Hz and 30 degrees C. Cocaine decreased peak cell shortening and peak intracellular Ca2+ in a concentration-dependent manner (10(-8)-10(-4) M). The concentration-response curve of cocaine was shifted significantly downward compared with those of lidocaine and procaine in the same range of concentrations. Atropine (10(-6) M) shifted the concentration-response curve of cocaine, but not those of lidocaine and procaine, rightward, with a pA2 value (7.66) similar to that obtained with carbachol (7.99). With prior addition of isoproterenol (ISO, 10(-8) M) or increased Ca2+ (4.0 mM) to increase cell shortening to the same degree (approximately 60%), cocaine and carbachol decreased contractility to a significantly greater extent in ISO-stimulated myocytes. To clarify whether these treatments changed responsiveness of the contractile elements to Ca2+, the effect of 2,3-butanedione monoxime, an agent that interferes with the interaction of myosin and actin, was tested with previous addition of ISO or increased Ca2+, and no differential effect occurred. Therefore, we postulate that 1) the NIE of cocaine on myocytes is caused by decreased Ca2+ availability; 2) this effect is due to specific stimulation of cholinergic receptors in addition to other direct myocardial (probably local anesthetic) effects; and 3) the NIE correlates with the level of cAMP dependence of the inotropic state.

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Muscarinic receptor subtype mediating vasodilation in feline middle cerebral artery exhibits M3 pharmacology

European Journal of Pharmacology ◽

10.1016/0014-2999(90)90476-m ◽

1990 ◽

Vol 178 (2) ◽

pp. 203-213 ◽

Cited By ~ 62

Author(s):

François Dauphin ◽

Edith Hamel

Keyword(s):

Middle Cerebral Artery ◽

Muscarinic Receptor ◽

Cerebral Artery ◽

Receptor Subtype ◽

Muscarinic Receptor Subtype

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Muscarinic receptor subtype-specific effects on cigarette smoke-induced inflammation in mice

European Respiratory Journal ◽

10.1183/09031936.00112412 ◽

2013 ◽

Vol 42 (6) ◽

pp. 1677-1688 ◽

Cited By ~ 30

Author(s):

Loes E.M. Kistemaker ◽

I.S.T. Bos ◽

Machteld N. Hylkema ◽

Martijn C. Nawijn ◽

Pieter S. Hiemstra ◽

...

Keyword(s):

Muscarinic Receptor ◽

Cigarette Smoke ◽

Receptor Subtype ◽

Muscarinic Receptor Subtype ◽

Specific Effects

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Mechanical and electrophysiological effects of a hydroxyphenyl-substituted tetrahydroisoquinoline, SL-1, on isolated rat cardiac tissues

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y95-727 ◽

1995 ◽

Vol 73 (11) ◽

pp. 1651-1660 ◽

Cited By ~ 3

Author(s):

Gwo-Jyh Chang ◽

Ming-Jai Su ◽

Pei-Hong Lee ◽

Shoei-Sheng Lee ◽

Karin Chiung-Sheue Liu

Keyword(s):

Action Potential ◽

Action Potential Duration ◽

Positive Inotropic Effect ◽

Ventricular Myocytes ◽

Inotropic Effect ◽

Dependent Manner ◽

Cardiac Tissues ◽

Inward Current ◽

Adrenoceptor Antagonist ◽

Isolated Rat

The mechanisms of the positive inotropic action of a new synthetic tetrahydroisoquinoline compound, SL-1, were investigated in isolated rat cardiac tissues and ventricular myocytes. SL-1 produced a rapidly developing, concentration-dependent positive inotropic response in both atrial and ventricular muscles and a negative chronotropic effect in spontaneously beating right atria. The positive inotropic effect was not prevented by pretreatment with reserpine (3 mg/kg) or the α-adrenoceptor antagonist prazosin (1 μM), but was suppressed by either the β-adrenoceptor antagonist atenolol (3 μM) or the K+ channel blocker 4-aminopyridine (4AP, 1 mM). In the whole-cell recording study, SL-1 increased the plateau level and prolonged the action potential duration in a concentration-dependent manner and decreased the maximum upstroke velocity [Formula: see text] and amplitude of the action potential in isolated rat ventricular myocytes stimulated at 1.0 Hz. On the other hand, SL-1 had little effect on the resting membrane potential, although it caused a slight decrease at higher concentrations. Voltage clamp experiments revealed that the increase of action potential plateau and prolongation of action potential duration were associated with an increase of Ca2+ inward current (ICa) via the activation of β-adrenoceptors and a prominent inhibition of 4AP-sensitive transient outward K+ current (Ito) with an IC50 of 3.9 μM. Currents through the inward rectifier K+ channel (IKl) were also reduced. The inhibition of Ito is characterized by a reduction in peak amplitude and a marked acceleration of current decay but without changes on the voltage dependence of steady-state inactivation. In addition to the inhibition of K+ currents, SL-1 also inhibited the Na+ inward current (INa) with an IC50 of 5.4 μM, which was correlated with the decrease of [Formula: see text]. We conclude that the positive inotropic effect of SL-1 may be due to an increase in Ca2+ current mediated via partial activation of β-adrenoceptors and an inhibition of K+ outward currents and the subsequent prolongation of action potentials.Key words: SL-1, tetrahydroisoquinoline, inotropic and chronotropic action, action potential, Na+, Ca2+, and K+ currents.

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