Reciprocal ST segment changes reproduced in burn-induced subepicardial injury model in bullfrog heart

Sodium bicarbonate and salbutamol facilitate recovery from hyperkalemia-induced electrocardiogram abnormalities in bullfrog hearts

Hyperkalemia is a common electrolyte abnormality frequently complicated with chronic kidney disease. By injecting potassium chloride (KCl) solutions intravenously into bullfrogs, we reproduced typical electrocardiogram (ECG) abnormalities of hyperkalemia in the frog hearts, such as the peaked T waves and the widening of QRS complexes. Simultaneous recordings of cardiac action potentials showed morphological changes that synchronized with those of ECG. After 100 mM KCl injection, the widened QRS complexes continued for a while and gradually restored to their baseline widths. However, pre-treatment with sodium bicarbonate or salbutamol, which directly or indirectly stimulates Na+/K+-ATPase activity, significantly facilitated the recovery from the widened QRS duration, indicating the transcellular movement of potassium ions from the extracellular fluid into the intracellular stores.

Amitriptyline intoxication in bullfrogs causes widening of QRS complexes in electrocardiogram

Amitriptyline intoxication is caused by its suicidal or accidental overdose. In the present study, by intravenously injecting 1.5 or 3.0 mg/kg amitriptyline into bullfrogs, we actually revealed that amitriptyline causes the widening of QRS complexes in electrocardiogram (ECG). In simultaneous recordings of the cardiac action potential, amitriptyline decreased the slope of phase 0 in the action potential, indicating the inhibition of the inward sodium currents during this phase. The following treatment with sodium bicarbonate quickly restored the widened QRS complexes in the ECG, demonstrating the counteraction with the sodium channel blockade caused by amitriptyline. The dual recordings of ECG waveforms and the action potential in cardiomyocytes enabled us to demonstrate the mechanisms of characteristic ECG abnormalities caused by amitriptyline intoxication.

Subepicardial burn injuries in bullfrog heart induce electrocardiogram changes mimicking inferior wall myocardial infarction

Using bullfrog hearts, we previously reproduced a ST segment elevation in electrocardiogram (ECG), mimicking human ischemic heart disease. In the present study, by inducing subepicardial burn injuries on the inferior part of the frog heart ventricle, we could reproduce typical ECG changes observed in human inferior wall myocardial infarction, such as the marked elevation of the ST segments in inferior limb leads (II, III, aVF) and their reciprocal depression in the opposite limb leads (I, aVL). Due to the decrease in Na⁺/K⁺-ATPase protein expression, the resting membrane potential of injured cardiomyocytes shifted toward depolarization. Such induced electrical difference between the injured and intact cardiomyocytes was thought to be responsible for the creation of “currents of injury” and the subsequent ST segment changes.

Insulin accelerates recovery from QRS complex widening in a frog heart model of hyperkalemia

Hyperkalemia is one of the most common electrolyte disorders. By injecting various concentrations of potassium chloride (KCl) solutions intravenously into bullfrogs, we demonstrated characteristic electrocardiogram (ECG) abnormalities of hyperkalemia in frog hearts. The widened QRS complexes induced by 100 mM KCl injection were accompanied by an increase in the resting membrane potential in cardiomyocytes and a decreased slope of phase 0 in the action potential. Recording both ECG waveforms and the cardiac action potential enabled us to reveal the mechanisms of hyperkalemia-induced ECG abnormalities. Additionally, pre-treatment with insulin, a powerful stimulator of Na⁺/K⁺-ATPase activity, significantly accelerated the recovery from the widened QRS complexes in the ECG, demonstrating a pronounced shift of extracellular potassium ions into the intracellular space.

High-magnesium exposure to bullfrog heart causes ST segment elevation

Hypermagnesemia occurs in elderly people or patients with renal insufficiency after excessive ingestion of magnesium-containing laxatives. In addition to typical electrocardiogram (ECG) findings caused by conduction defects, changes in the ST segments and T waves are also observed in patients with severe hypermagnesemia. This suggested the involvement of similar pathophysiology to acute myocardial infarction, as we previously demonstrated using burn-induced subepicardial injury model in frog hearts. In the present study, by exposing the bullfrog heart to high-magnesium solution, we reproduced prominent ST segment changes in ECG as actually observed in patients with severe hypermagnesemia. In addition to the great increase in the T waves, the ECG showed a marked elevation of the ST segments and the cardiac action potential demonstrated a marked shift of the resting membrane potential to the depolarized side. High-magnesium exposure did not affect the abundance of Na⁺/K⁺-ATPase proteins. However, the pharmacological stimulation of Na⁺/K⁺-ATPase activity by insulin quickly retrieved the elevated ST segments in ECG. From these results, the functional blockade of Na⁺/K⁺-ATPase activity by magnesium ions was thought to be responsible for generating the potassium concentration gradient and the subsequent ST segment changes.