Beta-adrenergic modulation of Na-K pump activity in young and adult canine cardiac Purkinje fibers

We used standard microelectrode techniques to study the developmental changes and beta-adrenergic modulation of membrane potential and of Na-K pump activity in adult (> 1 yr of age) and neonatal (2-10 days) canine Purkinje fibers. Isoproterenol (10(-7) M) increased the rate of development and magnitude of pacing-induced hyperpolarization of adult fibers driven at a 1-s cycle length. This effect of isoproterenol was attenuated by treating dogs with pertussis toxin (PTX), (30 micrograms/kg). Other adult and neonatal fibers were superfused with a Tyrode solution containing Ba2+ 0.2 mM, Cs+ 2 mM, and 10(-6) M verapamil, thus leading to depolarization and cessation of spontaneous activity. The Na-K pump was studied by alternating solutions containing [K] at 0 mM (inhibiting the pump) and 4 mM (reactivating the pump). Although the kinetics of the Na-K pump appeared faster in neonatal fibers than in adult fibers, measurement of cell surface-to-volume ratio compensated for the difference. We therefore conclude that 1) the apparent age-related changes in Na-K pump activity in canine Purkinje fibers in fact reflect cell surface-to-volume ratio and, 2) the beta-adrenergic agonist-induced hyperpolarization in adults requires the presence of a PTX-sensitive G protein for its occurrence.

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Electrophysiological Differences in the CPG Aerial Respiratory Behavior Between Juvenile and Adult Lymnaea

Journal of Neurophysiology ◽

10.1152/jn.00263.2003 ◽

2003 ◽

Vol 90 (2) ◽

pp. 983-992 ◽

Cited By ~ 20

Author(s):

Chlöe McComb ◽

Ryanne Meems ◽

Naweed Syed ◽

Ken Lukowiak

Keyword(s):

Volume Ratio ◽

Rhythmic Activity ◽

Membrane Resistance ◽

Synaptic Connectivity ◽

Aerial Respiration ◽

Respiratory Rhythmogenesis ◽

Age Related ◽

Respiratory Behavior ◽

The Difference ◽

Cutaneous Respiration

Intact, freely moving juvenile Lymnaea perform aerial respiration significantly less often than do adults. We therefore hypothesized that RPeD1, the central pattern generator (CPG) neuron that initiates rhythmogenesis, would be less active in juveniles than adults. Using both isolated and semi-intact preparations to directly test this hypothesis, we found the opposite; juvenile RPeD1s were significantly smaller and more excitable than RPeD1s from adults. Significant age-related differences were found in the membrane resistance (greater in juveniles), time constant (smaller in juveniles), and rheobase current (lower in juveniles), all of which would tend to make juvenile cells significantly more excitable. However, there were significant age-related differences in the synaptic connectivity within the CPG and in peripheral input to the CPG, all which favor more rhythmic activity in the adult CPG. As was the case for intact Lymnaea, juvenile semi-intact preparations perform aerial respiration less often than do adults. The difference in excitability between juvenile and adult RPeD1s is therefore not sufficient to cause increased rhythmogenesis. Age-related changes in synaptic connectivity within the respiratory CPG and in peripheral modulation allow respiratory rhythmogenesis to be more easily expressed in adults which may compensate for their decreased dependence on cutaneous respiration as their surface to volume ratio changes as the grow in size.

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Beta-adrenergic modulation of pulmonary transvascular fluid and protein exchange

Journal of Applied Physiology ◽

10.1152/jappl.1986.60.1.266 ◽

1986 ◽

Vol 60 (1) ◽

pp. 266-274 ◽

Cited By ~ 27

Author(s):

F. L. Minnear ◽

A. Johnson ◽

A. B. Malik

Keyword(s):

Control Group ◽

Protective Effects ◽

Beta Adrenergic ◽

Intravascular Coagulation ◽

Protein Clearance ◽

Adrenergic Antagonist ◽

Adrenergic Modulation ◽

Pulmonary Arterial ◽

Beta Adrenergic Agonist ◽

Protein Exchange

We determined in anesthetized sheep whether isoproterenol, a beta-adrenergic agonist, prevents the increases in pulmonary fluid and protein exchange produced by thrombin-induced intravascular coagulation. Seven sheep were infused intravenously with 0.05 micrograms X kg-1 X min-1 isoproterenol before infusion of alpha-thrombin, and six sheep were infused with alpha-thrombin only and served as control subjects. The marked increases in pulmonary lymph flow and lymph protein clearance in the control thrombin group were attenuated (P less than 0.05) in the isoproterenol group in association with a higher pulmonary blood flow (P less than 0.05) and a lower pulmonary vascular resistance (P less than 0.05) in the isoproterenol group and with similar increases in pulmonary arterial and pulmonary arterial wedge pressures in both groups. The decreases in fluid and protein fluxes produced by isoproterenol are related to its beta-adrenergic properties because propranolol, a beta-adrenergic antagonist, blocked the protective effects of isoproterenol in a second group of sheep infused with propranolol, isoproterenol, and thrombin. Raising left atrial pressure to test for changes in vascular permeability increased protein flux to a much greater extent in the thrombin control group than in the isoproterenol group challenged with thrombin. The data suggest that isoproterenol attenuated the increase in fluid and protein fluxes produced by thrombin-induced intravascular coagulation by a permeability-decreasing mechanism.

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Activated protein C generation is greatly decreased in plasma from newborns compared to adults in the presence or absence of endothelium

Thrombosis and Haemostasis ◽

10.1160/th03-06-0372 ◽

2004 ◽

Vol 91 (02) ◽

pp. 238-247 ◽

Cited By ~ 5

Author(s):

Sanjay Patel ◽

Christoph Male ◽

Leslie Berry ◽

Lesley Mitchell ◽

Anthony Chan

Keyword(s):

Cell Surface ◽

Tissue Factor ◽

Umbilical Cord ◽

Protein C ◽

Thrombin Generation ◽

Activated Protein C ◽

Age Related ◽

Adult Plasma ◽

The Difference ◽

Inhibition Of Thrombin

SummaryActivated protein C (APC) generation strongly affects sepsis and thrombosis by inhibition of thrombin generation. However, it is unclear if there are age-related differences in effectiveness of protein C (PC). We studied age effects on plasma APC generation ± endothelium. Defibrinated (Ancrod) plasma (from adults or newborns (umbilical cord)) was recalcified with buffer containing tissue factor ± thrombomodulin (TM) on either plastic or endothelium (HUVEC) at 37oC. Timed subsamples of reaction mixture were taken into either heparin-EDTA or FFRCMK-EDTA solutions and analyzed for APC-PC inhibitor (APC-PCI) or APC-α1antitrypsin (APC-α1AT) by ELISAs. Since heparin converts free APC to APC-PCI, the difference in APCPCI measured in heparin-EDTA and FFRCMK-EDTA samples was equal to free active APC. APC-α2macroglobulin (APC-α2M) was measured as remaining chromogenic activity in heparin-EDTA. Free APC, APC-PCI and APC-α1AT were decreased in newborn compared to adult plasma on plastic. However, APC-α2M made up a larger fraction of inhibitor complexes in newborn plasma. On endothelium, significantly more APC, APC-PCI and APC-α1AT were generated in either plasma compared to that on plastic with excess added TM. APC, APC-PCI and APC-α1AT were also reduced and total APC-α2M increased in newborn plasma on HUVEC. Addition of PC to newborn plasma gave APC generation similar to adult plasma. Thus, free APC, APC-PCI and APC-α1AT generation is reduced in newborn compared to adult plasma with or without endothelium, likely due to reduced plasma PC levels. Endothelium enhances APC generation, regardless of plasma type, possibly because of cell surface factors such as TM, phospholipid and endothelial PC receptor.

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Adrenergic modulation of the delayed rectifier potassium channel in calf cardiac Purkinje fibers

Biophysical Journal ◽

10.1016/s0006-3495(86)83713-4 ◽

1986 ◽

Vol 49 (4) ◽

pp. 839-848 ◽

Cited By ~ 43

Author(s):

P. Bennett ◽

L. McKinney ◽

T. Begenisich ◽

R.S. Kass

Keyword(s):

Potassium Channel ◽

Delayed Rectifier ◽

Purkinje Fibers ◽

Cardiac Purkinje Fibers ◽

Adrenergic Modulation ◽

Delayed Rectifier Potassium Channel ◽

Rectifier Potassium Channel

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Electrophysiological effects of alpha 2-adrenergic stimulation in canine cardiac Purkinje fibers

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1995.268.5.h2024 ◽

1995 ◽

Vol 268 (5) ◽

pp. H2024-H2035 ◽

Cited By ~ 3

Author(s):

R. A. Samson ◽

J. J. Cai ◽

E. F. Shibata ◽

J. B. Martins ◽

H. C. Lee

Keyword(s):

Action Potential ◽

Pertussis Toxin ◽

Adrenergic Stimulation ◽

Beta Adrenergic ◽

Purkinje Fibers ◽

Cardiac Purkinje Fibers ◽

Action Potential Prolongation ◽

Delayed Afterdepolarizations ◽

Baseline Values ◽

Electrophysiological Effects

The effects of alpha 2-adrenergic stimulation on action potentials were measured in isolated canine Purkinje fibers. Action potential durations at 50 and 90% of repolarization (APD50 and APD90) were significantly prolonged by 0.25 microM l-norepinephrine + 0.5 microM dl-propranolol (NE+P) from baseline values of 166 +/- 7 and 249 +/- 9 (SE) ms (n = 7) to 174 +/- 7 and 265 +/- 9 ms, respectively (P < 0.05 for both). Selective alpha 2-blockade with 0.01 microM yohimbine (YO) reduced this prolongation by NE+P in APD50 and APD90 to 169 +/- 7 and 256 +/- 8 ms, respectively (P < 0.05 compared with NE+P). Additional selective alpha 1-blockade with 0.01 microM prazosin (PZ) completely blocked the effects of NE+P, returning APD50 and APD90 to 163 +/- 7 and 250 +/- 9 ms (not different from baseline). After incubation of isolated Purkinje fibers with pertussis toxin (1 microgram/ml), which reduced the availability of a 41-kDa membrane protein for ADP ribosylation by 70 +/- 7% (n = 4, P < 0.05), YO failed to reverse the prolongation in action potential durations brought on by NE+P, but the effects of PZ were intact. The effects of alpha 2-stimulation on beta-adrenergic-induced delayed afterdepolarizations (DADs) were studied by burst pacing of Purkinje fibers in Tyrode solution containing 7.5 mM Ca2+. The DADs induced in the presence of NE+PZ (beta- + alpha 2-stimulation) were significantly smaller in amplitude and required a shorter pacing cycle length to reach threshold than those induced in the presence of NE+PZ+YO (unopposed beta-adrenergic stimulation). Furthermore sustained triggered activity, seen in five of eight preparations under beta-stimulation, could no longer be elicited in the presence of beta- + alpha 2-stimulation. These results suggest that the postjunctional alpha 2-adrenergic receptors in canine Purkinje fibers are coupled to a pertussis toxin-sensitive G protein and that stimulation of these receptors leads to action potential prolongation and suppression of DADs induced by beta-adrenergic stimulation.

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