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[Nature of the phasic component of potassium contracture in the frog myocardium]
Abstract:
High concentrations (4 X 10(-6) g/ml) of D-600 or BAY-1040 applied for 15 min to rhythmically stimulated strip of frog ventricular myocardium inhibited both the twitches and the K-contracture phasic component induced by 200 mM K+ (in the presence of 110 mM Na+). The phasic component, however, also disappeared after a 15-20-min resting in the Ringer solution before substitution of the latter with high K solution. Such a suppression of the phasic component due to myocardiac inactivity was prevented by an increase in Ca ion concentration up to 10 mM or by addition of ouabain (5 X 10(-6) M) to the Ringer solution during the resting period. The increase in [Ca++]0 was effective even after a 15-min preliminary resting in the Ringer solution. In these conditions the amplitude of the phasic component increased as the time of myocardium exposure to high Ca Ringer solution was prolonged from 5 to 15 min. Loading of some intracellular Ca stores seems to be a prerequisite for the phasic K-contractures generation.
Insights
D-600 and BAY-1040 inhibit frog heart contractions. Calcium loading is essential for potassium-induced contractions, suggesting intracellular calcium stores are crucial for cardiac muscle function.
Area of Science:
- Cardiology
- Pharmacology
- Cell Physiology
Context:
- The study investigates the effects of specific pharmacological agents on cardiac muscle contractility.
- Understanding the role of calcium ions in myocardial function is critical for cardiovascular research.
Purpose:
- To examine the impact of D-600 and BAY-1040 on frog ventricular myocardium contractility.
- To elucidate the role of extracellular calcium and intracellular calcium stores in potassium-induced contractures.
Summary:
- High concentrations of D-600 or BAY-1040 inhibited frog ventricular myocardium twitches and the phasic component of potassium-induced contractures.
- The phasic component's disappearance during resting was prevented by increased extracellular calcium or ouabain, indicating calcium loading is necessary.
- Prolonged exposure to high calcium Ringer solution increased the phasic component's amplitude, supporting the prerequisite role of intracellular calcium stores.
Impact:
- This research provides insights into the mechanisms underlying cardiac contractility and the regulation by calcium.
- Findings contribute to the understanding of drug actions on the heart and potential therapeutic targets for cardiac conditions.