Changing ionic composition of the environment and applying exposures which modify the conductivity of electrogenic membrane, the role of entering and leaving currents is studied in the generation of two zones of repeated responses (RR) of cat papillary muscle fibres. The first RR zone activated at a weak depolarization of the membrane (no higher than 30 mV) seems to be concerned with the functioning of the fast Na system. It was not blocked with inderal (2 divided by 5 mg/l), anor with Mn2+ ions (3mM). The second RR zone appearing at a stronger membrane depolarization (higher than 30 mv) is essentially dependent on the activity of the slow Na-Ca-system. It is activated with adrenaline (0.2 mg/l), ions of Sr2+ (5mM), Ba2+ (0.1 mM), Ca2+ (5 divided by 10 mM); blocked with Mn2+ (3 mM), Co2+ (5mM) ions, verapamile (2 divided by 4 mg/l), inderal (2 divided by 4 mg/l). The second RR zone was essentially affected with potassium ions: the 3-fold increase of Ko+ suppressed the RR of the second zone, a 3-fold decrease of Ko+ strengthened them.

Animals↗

PubMedDate not supplied

[Dicrete zones of electrical connection between Purkinje terminals and muscle fibers in dog ventricles].

Activity of Purkinje terminals (P) and neighbouring muscle (M) fibres (P -- M-pairs) in various regions of dog's right ventricle was recorded. It has been shown that transmission of stimulation from P-to M-fibres is abserved not over all endocardial surface, rather in descrete sites -- zones of P--M-interaction. The zones ellips like with the axes 300X100 micron, they are located relatively far from one another -- at the distance of 800-2000 microns. The total area of the zones equals 5% of endocardial surface. P-M delay is less within the zone of connection of P--M-fibres (4 msec) and greater outside the zone (up to 10 msec).

Action Potentials↗

PubMedDate not supplied

[Evoked automatism (repeated responses) of cat cardiac ventricular fibers].

Repeated responses (RR) of cat papillary muscle fibres have been studied. Threshold current of the occurrence of repeated responses (2t) and saturation current (Is) on the accomodation curve have been determined. Two zones of autooscillations were revealed according to the ratio brage from low levels of the membrane potential (-80 divided by -55 mv). The second RR zone (It is not equal to Is) was activated in more than 70 per cent of preparations in the average from higher levels of the membrane potential (-40 mv and higher). A comparison was carried out between muscle and specialized fibres RR. The experimental data were analysed by the method of phase plane.

Animals↗

PubMedDate not supplied

[Anisotropy of stationary rates and delays in extrasystolic waves in the dog heart].

Excitation propagation in the ventricle and auricle bands of the dog's myocardium has been studied. The anisotropy of stationary valocities and delays of the initiation of extrasistole exciation has been shown: along the fibres the velocity is higher and the delay smaller than across the fibres. The levels of anisotropy of velocities and delays are almost equal in each structure. The strongest anisotropy of delays and velocities (-4,5) is observed in the ventricle muscle layer; the weakest (1,7)-in a specialized layer. The anisotropy of velocities and delays is the greater, the greater is the electrotone anisotropy. A new mechanism of extrasistole initiation (reentry) in the system homogenous by the membrane properties, but with anisotropy of intercellular bonds is considered.

Animals↗

PubMedDate not supplied

[Role of entering currents in the accommodation of myocardial fibers].

Varying ionic composition of outher medium and applying specific agents the role of fast and slow systems of entering currents in the accommodation of cats ventricular fibres has been studied. In potential region close to the level of resting potential (membrane depolarization no larger than 20-30mv), accomodation mainly depends on fast sodium currents. It is inhibited with a rise of this current (akonitin 0.1--1 mg) and, on the contrary, it increases when it gets weaker (novacain 2--5 mM). In the region of more positive potentials (membrane depolarization more than by 30 mv) the accommodation is mainly determined by the slow NA--Ca-systems of channels. The agents which strengthen NA--Ca--current (Si2+--5mM, Ca2+--10mM, Ba2+--0.1 mM) reduce the accommodation in the activation region of the Na--Ca--system. The agents which weaken the slow current (Mn2+--3 mM, isoptin--2+5 mg/l, inderal--2 mg/l) produce an opposite effect.

Aconitine↗

PubMedDate not supplied

[Potential- and stimulus-dependence of the effect of dihydropyridine Ca-agonists on calcium channels in heart fibers].

It has been shown on the frog auricle fibres by the method of double sucrose bridge that the dependence of the effect of dihydropyridine Ca agonists BAYK 8644, CGP 28 392 and (-S)202 = 791 on calcium channels on the membrane potential is to a large extent due to the activation and following inactivation of Ca channels "silent" in the control. This effect takes place due to a shift by Ca agonists of the stationary curve of channel activation to hyperpolarization. The absence of stimulus-dependence of the agonist effect and constant time of Ca current reactivation suggest that the agonists bind with resting channels.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMedDate not supplied