Developmental Differences in the Electrophysiological Response of Isolated Canine Purkinje Fibers to Adrenergic Stimulation during Simulated Ischemia

1993 ◽  
Vol 20 (1-2) ◽  
pp. 72-85 ◽  
Author(s):  
Arnold Fenrich ◽  
Mary Hamra
Keyword(s):  
Developmental Differences ◽  
Adrenergic Stimulation ◽  
Electrophysiological Response ◽  
Purkinje Fibers ◽  
Simulated Ischemia

Beta-adrenergic regulation of action potentials and automaticity in young and adult canine purkinje fibers

1994 ◽  
Vol 266 (6) ◽  
pp. H2310-H2319
Author(s):  
F. Charpentier ◽  
M. R. Rosen
Keyword(s):  
Cycle Length ◽  
Beta Agonist ◽  
Adrenergic Stimulation ◽  
Beta Adrenergic ◽  
Purkinje Fibers ◽  
Transmembrane Potentials ◽  
Beta 2 ◽  
Electrophysiological Effects ◽  
Microelectrode Techniques ◽  
Diastolic Potential

To investigate developmental changes in the cellular electrophysiological effects of beta 1- and beta 2-adrenoceptor stimulation on canine Purkinje fibers (PF), we studied the effects of isoproterenol, a nonselective beta-agonist, and salbutamol, a preponderantly beta 2-agonist, alone or in presence of the selective beta 1-antagonist CGP-20712A or the beta 2-antagonist ICI-118551. Standard microelectrode techniques were used to study adult and neonatal (< 11 days) PF paced at a cycle length of 1 s or allowed to beat spontaneously. In paced adult PF, isoproterenol significantly increased the maximum diastolic potential and significantly decreased action potential duration at 60 and 90% of full repolarization (APD60 and APD90) in a concentration-dependent fashion. These effects were not observed in neonatal PF, which instead manifested a significant increase in phase 2 amplitude and APD30 that was not observed in adult PF. All these effects occurred as well with salbutamol but were less pronounced and required higher agonist concentrations. Isoproterenol decreased the automatic cycle length of adult fibers from 4,079 +/- 796 ms during control to 2,190 +/- 229 ms at 10(-5) M (P < 0.05) and from 1,535 +/- 105 to 1,249 +/- 90 ms in neonatal PF (P < 0.05). In both adults and neonates, > 90% of this effect was reached at a concentration of 10(-8) M. Salbutamol had the same effect but required higher concentrations. In both adults and neonates, the beta 2-antagonist ICI-118551 did not modify any of the effects of isoproterenol and salbutamol, whereas the beta 1-antagonist CGP-20712A significantly antagonized them. In conclusion, 1) the effects of beta-adrenergic stimulation on transmembrane potentials of canine PF change during development, both qualitatively (in paced PF) and quantitatively (in automatic PF) and 2) the responses seen are attributable to the activation of beta 1- and not beta 2-adrenoceptors.

Differences in automaticity between Purkinje strands from right and left dog ventricle

1980 ◽  
Vol 239 (2) ◽  
pp. H247-H251
Author(s):  
J. Reiser ◽  
G. J. Anderson
Keyword(s):  
Intrinsic Rate ◽  
Adrenergic Blockade ◽  
Adrenergic Stimulation ◽  
Purkinje Fibers ◽  
Chronotropic Response ◽  
Cycle Lengths ◽  
Left And Right ◽  
Ventricular Conduction

Previous in situ studies have implicated differences in the pacemaker rates between the left and right ventricular conduction system. Our studies were conducted to characterize automaticity in peripheral right and left canine Purkinje fibers in vitro. Standard microelectrode techniques were utilized. In paired right (RPF) and left (LPF) canine Purkinje fibers, control intrinsic rate (IR) was found to be higher in LPF (24.8 +/- 1.7 beats/min) than in RPF (11.5 +/- 1.5 beats/min, P less than 0.01). Following overdrive stimulation at various cycle lengths, LPF consistently showed earlier escape beats. In low K0+ (1.35 mM), IR increased comparably in both RPF and LPF. However, high K0+ (5.4 mM) resulted in a greater reducton of the IR in RPF (-78%) than in LPF (-58%). After epinephrine (10(-6) M) the IR of LPF > RPF although the chronotropic response was more pronounced in RPF. Adrenergic stimulation preceded by beta-adrenergic blockade did not produce significant differences in the intrinsic rate between RPF and LPF. These findings indicate that automaticity in right and left Purkinje strands is functionally dissimilar.

Developmental differences in L-type calcium current of human atrial myocytes

2004 ◽  
Vol 286 (5) ◽  
pp. H1963-H1969 ◽  
Author(s):  
Srinivas M. Tipparaju ◽  
Rajiv Kumar ◽  
Yanggan Wang ◽  
Ronald W. Joyner ◽  
Mary B. Wagner
Keyword(s):  
Older Adult ◽  
Calcium Current ◽  
Low Dose ◽  
Developmental Differences ◽  
Right Atrial ◽  
Atrial Myocytes ◽  
Adrenergic Stimulation ◽  
Inhibitory Effects ◽  
Human Atrial Myocytes ◽  
Protein Levels

We investigated differences in L-type Ca2+ current ( ICa) between infant (INF, 1–12 mo old), young adult (YAD, 14–18 yr old), and older adult (AD) myocytes from biopsies of right atrial appendages. Basal ICa was smaller in INF myocytes (1.2 ± 0.1 pA/pF, n = 29, 6 ± 1 mo old, 11 patients) than in YAD (2.5 ± 0.2 pA/pF, n = 20, 16 ± 1 yr old, 5 patients) or AD (2.6 ± 0.3 pA/pF, n = 19, 66 ± 3 yr old, 9 patients) myocytes ( P < 0.05). Maximal ICa produced by isoproterenol (Iso) was similar in INF, YAD, and AD cells: 8.4 ± 1.1, 9.6 ± 1.0, and 9.2 ± 1.3 pA/pF, respectively. Efficacy (Emax) was larger in INF (607 ± 50%) than for YAD (371 ± 29%) or AD (455 ± 12%) myocytes. Potency (EC50) was 8- to 10-fold higher in AD (0.82 ± 0.09 nM) or YAD (0.41 ± 0.14 nM) than in INF (7.6 ± 3.5 nM) myocytes. Protein levels were similar for Giα2 but much greater for Giα3 in INF than in AD or YAD atrial tissue. When Giα3 activity was inhibited by inclusion of a Giα3 COOH-terminal decapeptide in the pipette, basal ICa and the response to 10 nM Iso were increased in INF, but not in YAD, cells. We propose that basal ICa and the response to low-dose β-adrenergic stimulation are inhibited in INF (but not YAD or AD) cells as a result of constitutive inhibitory effects of Giα3.

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

1995 ◽  
Vol 268 (5) ◽  
pp. H2024-H2035 ◽  
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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