Electrophysiologic effects of nicainoprol, a putative class I antiarrhythmic agent, on the guinea pig ventricular papillary muscle.

We examined the effects of nicainoprol (1-50 microM), a new antiarrhythmic agent, on the transmembrane action potentials in isolated papillary muscles of the guinea pig. Nicainoprol (greater than or equal to 5 microM) produced dose-dependent decreases in the maximal upstroke velocity (Vmax) of the action potential. Only the highest concentration (50 microM) decreased the amplitude and the overshoot of the action potential and shortened its duration at 50 or 90% repolarization levels (APD50, APD90).

Unaffected electrogenic Na-K pump activity in "diseased" human atrial fibers, as assessed by intracellular K+ activity.

To investigate the role of the electrogenic Na-K pump in the resting membrane of "diseased" or "depolarized" human atrial muscles, intracellular K+ activity (aiK) and resting membrane potential (Vm) were simultaneously measured using double-barreled K(+)-selective microelectrodes. Under perfusion with normal Tyrode's solution (37 degrees C) containing 5.4 mM [K]o, Vm averaged -43.

Two differential mechanisms of automaticity in diseased human atrial fibers.

The ionic mechanisms of automaticity in spontaneously active preparations (n = 38) from "diseased" human atria were investigated. The cycle length (CL) of the automatic action potential (AAP) ranged from 0.6 to 4.

Electrophysiologic properties differ in the ventricular endocardium and epicardium of the Japanese monkey.

We measured action potential duration (APD) from the endocardium (Endo) and epicardium (Epi) of the left ventricular free wall in Japanese monkey hearts and found that the APD of Endo is significantly longer than that of Epi at a stimulus cycle length of 1500 msec in normal Tyrode solution (control condition). We then hypothesized that shorter APD of Epi results from greater outward pump current and that the difference in the current may be due to a difference in membrane Na,K-ATPase activity between Endo and Epi. If this were the case, interventions which alter the Na,K-pump activity should alter electrophysiologic characteristics in the endocardium and the epicardium to different degrees.

Factors related to the low resting membrane potentials of diseased human atrial muscles.

We studied the ionic mechanism of low resting potential (RP) of quiescent "diseased" human atrial fibers. The RP was -49.7 +/- 0.

Na,K-ATPase activity and repolarization of ventricular action potentials in simian hearts.

We measured Na,K-ATPase activity and ATP content of 4 different areas of the left ventricular muscle of Japanese monkeys (Mucaca fuscata): The apex, base, and epicardium (Epi) and endocardium (Endo) of the free wall. We compared those values with electrical parameters such as action potential duration (APD) and the level of resing potentials. APDs of base and Endo were significantly longer than those of apex and Epi, respectively.

Isoproterenol inhibits residual fast channel via stimulation of beta-adrenoceptors in guinea-pig ventricular muscle.

When perfused with high K+ (8.1 to 14.9 mM)-Tyrode's solution, the upstroke of action potentials in the isolated guinea-pig ventricular muscle is composed of two components and there are two separable peaks in the first derivative, i.

Antiarrhythmic effects of nicorandil on canine cardiac Purkinje fibers.

Antiarrhythmic efficacy of nicorandil (SG-75) (1-100 microM), a coronary vasodilator, was investigated electrophysiologically with regard to the action potentials of canine Purkinje fibers. The main results obtained are as follows: (a) nicorandil suppressed three kinds of automaticities, i.e.

Electrocardiogram and His bundle electrogram of Japanese monkeys (Macaca fuscata).

Electrocardiogram (ECG) was taken from Macaca fuscata in the supine position under secobarbital anesthesia. The ECGs were recorded in the leads of standard (I, II, III), augmented unipolar limb (aVR, aVL, aVF) and unipolar chest (V4R, V1, V2, V3, V4, V5, V6,). The ECG was similar to that of humans as well as the monkeys of other species in their general patterns and the voltage of each wave (P, Q, R, S, T), though the heart rate was considerably different.

Nature of "residual fast channel" dependent action potentials and slow conduction in guinea pig ventricular muscle and its modification by isoproterenol.

The nature of "residual fast channel" dependent action potentials and conduction was studied in guinea pig ventricular papillary muscle in which the resting potential was reduced to 58 +/- 1 mV in high K+ (16.7 mM) Tyrode's solution, with or without isoproterenol (0.1 microM).

Effects of SG-75 (nicorandil) on electrical activity of canine cardiac Purkinje fibers: possible increase in potassium conductance.

The effects of various concentrations (1-1000 microM) of SG-75 nitrate or nicorandil) were investigated in action potentials of canine Purkinje fibers with microelectrodes. In normal fibers stimulated at the standard cycle length of 1500 msec, the drug (1-100 microM) produced dose-dependent shortening in action potential duration without changes in the resting potential, the maximum rate of rise of phase 0 and the slope of phase 4 depolarization. The drug-induced percentage of shortening in the action potential duration was more pronounced at lower rates of stimulation and lower external K+ concentrations, but the shortening was unchanged in lower external Na+ concentrations.

Na, K-ATPase activity, ATP and Pi concentrations in various regions of monkey heart and their relation to post-overdrive hyperpolarization.

The relationship among Na, K-ATPase activity, ATP and inorganic phosphate (Pi) concentrations in functionally different regions of cardiac and skeletal muscles were studied in the Japanese monkey (Macaca fuscata). The activity of Na, K-ATPase was determined by the method of FIske and SubbaRow, and the concentrations of ATP and Pi, by isotachophoresis. The ATP concentrations in several regions of cardiac and skeletal muscles correlated positively with the Na, K-ATPase activities and Pi concentrations, whereas there was no significant correlation between the Na, K-ATPase activities and the Pi concentrations.

Electrophysiological and inotropic effects of Coenzyme Q10 on guinea pig ventricular muscle depolarized by potassium under hypoxia.

The electrophysiological and inotropic effects of Coenzyme Q10 (CoQ10) on isoproterenol or barium-induced slow responses in ventricular papillary muscle, depolarized by high K+ concentration (21.6 mM) under hypoxia (PO2 = 40 mmHg), were studied with microelectrode techniques. For the isoproterenol-induced slow response, application of CoQ10 (50 micrograms/ml), which was emulsified with the aid of a special solvent, increased the maximum rate of rise of action potentials (Vmax), an indicator of the slow inward current, by about 40%, with no consistent effect on the action potential duration and developed tension.

Surface layer ATP-related contraction in isolated, superfused canine ventricular papillary muscle: an isotachophoretic analysis.

The relationship among contractile tension, ATP content and concentration was examined in isolated, superfused ventricular papillary muscle under normoxic (Po2 not equal to 300 mmHg) and hypoxic (Po2 not equal to 100 mmHg) conditions, using capillary isotachophoresis. The muscle preparations were exposed to each condition for 30 min, and the contractile tension was recorded with a strain gauge. Immediately after the recordings, the preparations were homogenized and the metabolites (ATP, ADP, AMP, creatine phosphate, inosine monophosphate, NAD, NADH, glucose-6-phosphate, pyruvate, and inorganic phosphate) were extracted in 50% methanol-1.

Isotachophoretic analyses of metabolites of cardiac and skeletal muscles in four species.

We studied ATP and concentrations of other metabolites in cardiac and skeletal muscles from different species (frog, hamster, guinea-pig, and dog), using analytical capillary isotachophoresis. The method had several advantages for quantitative analysis of tissue metabolites: short separation time, high sensitivity, high resolution, and good reproducibility. It was also possible to detect a number of compounds simultaneously, including ATP, ADP, AMP, cyclic AMP, creatine phosphate (CP), inosine monophosphate, NAD, NADH, glucose-6-phosphate, pyruvate, and inorganic phosphate.

The effects of verapamil and lidocaine on the automatic depolarizations in guinea-pig ventricular myocardium.

Rhythmic automatic depolarizations (RAD) were produced in guinea-pig papillary muscles depolarized to membrane potentials at which depolarizations depend on membrane currents passing through the slow channel. Verapamil depressed the RAD and decreased their overshoot. These verapamil effects were dependent on its concentration either in the bath (in vitro) or in plasma and myocardium (in vivo).

Isometric contraction and relaxation times of right and left ventricles in normal subjects and in patients with right ventricular overloading measured with bidirectional echocardiography.

With the use of bidirectional echocardiography, the isometric contraction (ICT) and relaxation times (IRT) of both ventricles were measured in 14 normal subjects (N), 6 cases with right ventricular (RV) diastolic overloading (DO), and 5 cases with RV systolic overloading (SO). The RVDO group consisted of patients with atrial septal defect of ostium secundum type who had large left-to-right shunting, and the RVSO group those with pulmonary hypertension of various origins. The mean ICT and IRT in N were 28.

Phono-, echo-, and electro-cardiographic correlation in the Wolff-Parkinson-White syndrome, with special reference to the split pattern of second heart sound.

Twenty-three cases with WPW syndrome were studied by means of phonocardiography, echocardiography, and electrocardiography. All cases showed the abnormal cardiac motion in echocardiography, which could be divided into 2 types; ventricular (V) type in which the posterior left ventricular wall showed the abnormal humps in the early and late systole (18 cases), and septal (S) type in which the abnormal hump was noted in the early systole in the interventricular septum (5 cases). The cases with V type echocardiogram showed either type A, B, or C, and those with S type either type B or C of ECG.

Automatic activity in depolarized guinea pig ventricular myocardium. Characteristics and mechanisms.

Membrane potential was changed uniformly in segments, 0.7-1.0 mm long, of guinea pig papillary muscles excised from the right ventricle by using extracellular polarizing current pulses applied across two electrically insulated cf preparations superfused with Tyrode's solution at maximum diastolic membrane potentials ranging from-35.