scholarly journals Depression of Slow Inward Current by Acetylcholine in Mammalian Ventricular Muscle

1978 ◽  
Vol 54 (8) ◽  
pp. 474-477 ◽  
Author(s):  
Rikuo OCHI ◽  
Naoki HINO
Keyword(s):  
Slow Inward Current ◽  
Ventricular Muscle ◽  
Inward Current

scholarly journals On the ionic mechanism underlying adrenergic-cholinergic antagonism in ventricular muscle.

1982 ◽  
Vol 79 (1) ◽  
pp. 69-86 ◽  
Author(s):  
I Josephson ◽  
N Sperelakis
Keyword(s):  
Reversal Potential ◽  
Outward Current ◽  
Cyclic Adenosine Monophosphate ◽  
Negative Inotropic Effect ◽  
Adenosine Monophosphate ◽  
Slow Inward Current ◽  
Ventricular Muscle ◽  
Adrenergic Stimulation ◽  
Inward Current ◽  
K Current

In atrial muscle, acetylcholine (ACh) decreases the slow inward current (Isi) and increases the time-independent outward K+ current. However, in ventricular muscle, ACh produces a marked negative inotropic effect only in the presence of positive inotropic agents that elevate cyclic adenosine monophosphate (AMP). A two-microelectrode voltage-clamp method was used on cultured reaggregates of cells from 16--20-d-old embryonic chick ventricles to determine the effects of ACh on Isi and outward current during beta-adrenergic stimulation. Only double penetrations displaying low-resistance coupling were voltage-clamped. Cultured reaggregates are advantageous because their small size (50--250 microns) permits better control of membrane potential and adequate space clamp. Tetrodotoxin (10(-6) M) and a holding potential of --50 to --40 mV were used to eliminate the fast Na+ current. Depolarizing voltage steps above --40 mV caused a slow inward current to flow that was sensitive to changes in [Ca]o and was depressed by verapamil (10(-6) M). Maximal Isi was obtained at --10 mV and the reversal potential was about +25 mV. Isoproterenol (10(-6) M) increased Isi at all clamp potentials. Subsequent addition of ACh (10(-6) M) rapidly reduced Isi to control values (before isoproterenol) without a significant effect on the net outward current measured at 300 ms. The effects of ACh were reversed by muscarinic blockade with atropine (5 X 10(-6) M). We conclude that the anti-adrenergic effects of ACh in ventricular muscle are mediated by a reduction in Ca2+ influx during excitation.

Voltage control during inward current flow in rat ventricular muscle using a double sucrose gap technique

1979 ◽  
Vol 57 (1) ◽  
pp. 124-127 ◽  
Author(s):  
O. F. Schanne ◽  
M. D. Payet ◽  
E. Ruiz P.-Ceretti
Keyword(s):  
Membrane Potential ◽  
Time Course ◽  
Voltage Control ◽  
State Level ◽  
Slow Inward Current ◽  
Ventricular Muscle ◽  
Time Intervals ◽  
Inward Current ◽  
Gap Technique ◽  
Sucrose Gap

In rat ventricular muscle, measurements of the membrane potential with microelectrodes during depolarizing voltage steps showed that deviation of the membrane potential from the command signal were never larger than 15 mV during flow of the fast inward current and that voltage control was regained within 15 ms after the beginning of the voltage step. During the flow of the slow inward current, tail currents elicited by interrupting the time course of the slow current at different time intervals returned exponentially to the steady-state level, thus indicating acceptable voltage control. It is concluded that rat ventricular muscle is a rather favorable preparation for voltage-clamp experiments and this is attributed mainly to the geometry of the preparation.

scholarly journals Slow inward current and contraction of sheep cardiac Purkinje fibers.

1975 ◽  
Vol 65 (3) ◽  
pp. 367-384 ◽  
Author(s):  
W R Gibbons ◽  
H A Fozzard
Keyword(s):  
Intracellular Calcium ◽  
Voltage Clamp ◽  
Mammalian Species ◽  
Slow Inward Current ◽  
Ventricular Muscle ◽  
Inward Current ◽  
Purkinje Fibers ◽  
Cardiac Purkinje Fibers ◽  
Rate Of Recovery ◽  
Calcium Pool

A "slow" inward current (Is) has been identified in ventricular muscle and Purkinje fibers of several mammalian species. The two-microelectrode voltage clamp technique is used to examine some of the relationships between Is and contraction of the sheep cardiac Purkinje fiber. "Tails" of inward current occurring on repolarization and extrapolation of Is recovery each show that the Is system may not inactivate completely during prolonged depolarization. The rate of recovery of Is after a depolarization is slow, and when a train of 300-ms clamps (frequency 1 s-1) is begun after a rest, Is is larger for the first clamp than it is for succeedings clamps. For the first clamp after a rest, the thresholds for Is and tension are the same and there is a direct correlation between peak tension and peak Is for clamp voltages between threshold and minus 40 mV. After a clamp, however, the ability to contract recovers much more slowly than does Is. Therefore, since Is may occur under certain conditions without tension, the realtionship between Is and tension must be indirect. Calcium entering the cell via this current may replenish or augment an intracellular calcium pool.

Three components of slow inward current in mammalian ventricular muscle

1990 ◽  
Vol 22 ◽  
pp. S21
Author(s):  
Jiří Šimurda ◽  
Milena Šimurdová ◽  
Pavel Bravený ◽  
Josef Šumbera
Keyword(s):  
Slow Inward Current ◽  
Ventricular Muscle ◽  
Inward Current ◽  
Three Components
Sign in / Sign up

Export Citation Format

Share Document