Phase resetting of spontaneously beating embryonic ventricular heart cell aggregates

1986 ◽  
Vol 251 (6) ◽  
pp. H1298-H1305 ◽  
Author(s):  
M. R. Guevara ◽  
A. Shrier ◽  
L. Glass
Keyword(s):  
Action Potentials ◽  
High Amplitude ◽  
Heart Cell ◽  
Cell Aggregates ◽  
Embryonic Chick ◽  
Phase Resetting ◽  
Stimulus Amplitude ◽  
High Stimulus ◽  
Very High ◽  
Spontaneous Rhythm

The influence of isolated 20-ms duration current pulses on the spontaneous rhythm of embryonic chick ventricular heart cell aggregates was studied. A pulse could either delay or advance the time of occurrence of the next action potential, depending on whether it fell early or late in the cycle. As the stimulus amplitude was increased, the transition from delay to advance occurred over a narrower range of coupling intervals. At low-stimulus amplitudes the transition from delay to advance occurred in a smooth continuous fashion; at medium-stimulus amplitudes the transition was discontinuous; at high-stimulus amplitudes graded action potentials were seen. It was impossible to annihilate spontaneous activity in aggregates with a single stimulus. The phase-resetting response to hyperpolarizing pulses was qualitatively the reverse of that produced by depolarizing pulses. A very high-amplitude depolarizing or hyperpolarizing pulse could produce rapid repetitive activity. Theoretical aspects of these phenomena are discussed.

Electrotonic interactions between aggregates of chick embryo cardiac pacemaker cells

1986 ◽  
Vol 250 (3) ◽  
pp. H453-H463 ◽  
Author(s):  
R. D. Veenstra ◽  
R. L. DeHaan
Keyword(s):  
Electrical Coupling ◽  
Cardiac Pacemaker ◽  
Heart Cell ◽  
Embryonic Chick ◽  
Phase Resetting ◽  
Pacemaker Cells ◽  
Beat Rate ◽  
Electrotonic Interactions ◽  
External K

Synchronization of spontaneously active heart cell aggregates occurs shortly after they are brought into contact. The synchronous rate is determined by pacemaker phase resetting and passive subthreshold electrotonic interactions. To further study the effects of passive electrical interactions, we have used 150-microns diameter aggregates prepared from cells of 4d (4-day ventricle + 1 day in vitro), 7d, and 14d embryonic chick ventricle as models of primary, latent, and nonpacemaker tissues, respectively. Coupling of 4d and 7d aggregates (4d/7d pairs) leads to intermediate synchronous rates. We show here that elevating external K+ from 1.3 to 2.8 mM, which has no effect on 4d/4d pairs but selectively reduces the beat rate of 7d/7d pairs by 42%, slows the synchronous beat rate of 4d/7d pairs by 23%. Increases in electrical coupling in newly joined 4d/14d pairs cause the 4d rate to slow to a minimum value (16 +/- 13 beats/min, n = 16) just prior to the onset of synchronous activity. The rate slowly recovers to a final value of 40 +/- 12 beat/min. We conclude that the spontaneous beat rate of a primary pacemaker is modulated by both active and passive interactions with latent or nonpacemaker tissues.

scholarly journals Junctional resistance and action potential delay between embryonic heart cell aggregates.

1980 ◽  
Vol 75 (6) ◽  
pp. 633-654 ◽  
Author(s):  
D E Clapham ◽  
A Shrier ◽  
R L DeHaan
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Time Course ◽  
Potassium Concentration ◽  
Aggregate Size ◽  
Heart Cell ◽  
Extracellular Potassium ◽  
Cell Aggregates ◽  
Extracellular Potassium Concentration ◽  
Junctional Resistance

Spheroidal aggregates of embryonic chick ventricle cells were brought into contact and allowed to synchronize their spontaneous beats. Action potentials were recorded with both intracellular and extracellular electrodes. The degree of electrical interaction between the newly apposed aggregates was assessed by measuring the delay or latency (L) between the entrained action potentials, and by determining directly interaggregate coupling resistance (Rc) with injected current pulses. Aggregate size, contact area between the aggregates, and extracellular potassium concentration (Ko+) were important variables regulating the time-course of coupling. When these variables were controlled, L and Rc were found to be linearly related after beat synchrony was achieved. In 4.8 mM Ko+ L/Rc = 3.7 ms/M omega; in 1.3 mM Ko+ L/Rc = 10.1 ms/M omega. We conclude that action potential delay between heart cell aggregates can be related quantitatively to Rc.

scholarly journals Ionic mechanisms and nonlinear dynamics of embryonic chick heart cell aggregates

1994 ◽  
Vol 61 (3) ◽  
pp. 255-281 ◽  
Author(s):  
Vijayanand C. Kowtha ◽  
Arkady Kunysz ◽  
John R. Clay ◽  
Leon Glass ◽  
Alvin Shrier
Keyword(s):  
Nonlinear Dynamics ◽  
Heart Cell ◽  
Cell Aggregates ◽  
Embryonic Chick ◽  
Ionic Mechanisms ◽  
Chick Heart ◽  
Embryonic Chick Heart

Overdrive suppression of spontaneously beating chick heart cell aggregates: experiment and theory

1995 ◽  
Vol 269 (3) ◽  
pp. H1153-H1164 ◽  
Author(s):  
A. Kunysz ◽  
L. Glass ◽  
A. Shrier
Keyword(s):  
Action Potentials ◽  
Main Idea ◽  
Heart Cell ◽  
Cell Aggregates ◽  
Ionic Model ◽  
Periodic Stimulation ◽  
Experimental Protocols ◽  
Chick Heart ◽  
Overdrive Suppression ◽  
Frequency Of Action Potentials

In spontaneously beating chick heart cell aggregates, sustained periodic stimulation at a rate faster than the intrinsic frequency is generally followed by a transient slowing of the automatic rhythm called "overdrive suppression." We characterize the qualitative aspects of overdrive suppression using three sets of experimental protocols: 1) stimulation at a fixed frequency with various numbers of stimuli, 2) stimulation at different frequencies, 3) stimulation with different intensities. We develop a mathematical model based on a system of nonlinear ordinary differential equations to account for the experimental observations. The main idea of the model is that overdrive suppression arises as a result of a hyperpolarizing current that is induced by action potentials. This work shows that the frequency of action potentials is the major determinant of overdrive suppression. Consequently, during periodic pacing of spontaneous oscillators at different rates, the fastest frequency where 1:1 entrainment can be maintained is associated with maximal overdrive suppression. This type of model is complementary to the development of a rigorous ionic model and can help provide insight into the physiological mechanisms of overdrive suppression.

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