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Positive staircase effect in the rat heart.

The American Journal of Physiology

|February 1, 1975

Summary

The positive staircase effect in rat hearts is observed when metabolic support, specifically glucose levels, is adequate. Insufficient glucose leads to cardiac mechanical deterioration and reduced ATP concentration.

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Area of Science:

Cardiovascular Physiology
Metabolic Support in Myocardium

Background:

The positive staircase effect (Bowditch phenomenon) is a fundamental property of cardiac muscle.
Previous studies suggested a lack of this effect in rat myocardium, potentially due to experimental conditions.

Purpose of the Study:

To investigate the role of metabolic support, particularly glucose availability, in eliciting the positive staircase effect in rat ventricular myocardium.
To determine if adequate metabolic conditions can reveal the positive staircase effect in isolated rat hearts and papillary muscles.

Main Methods:

Isolated rat hearts and papillary muscles were perfused/contracted under controlled conditions.
Experiments involved varying heart rates and perfusate glucose concentrations (5 mM and 30 mM).
Measurements included left ventricular pressure, dP/dt, myocardial ATP concentration, and isometric stress.

Main Results:

In isolated hearts with 5 mM glucose, high pacing rates (480/min) caused deterioration and decreased ATP.
In vivo (open-chest rats), hearts maintained normal ATP levels at high rates.
Isolated papillary muscles showed a decline in stress at high rates with 5 mM glucose but an increase with 30 mM glucose.

Conclusions:

Rat ventricular myocardium exhibits a positive staircase effect when metabolic support is adequate.
Sufficient glucose availability is crucial for maintaining cardiac function and demonstrating the positive staircase effect at physiological heart rates.

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