Comparison of voltage-tension relationship between peak and terminal tonic tensions induced by longer depolarization in the bullfrog myocardium

Abstract

1. 1. The comparison of voltage-tension relationship between peak and terminal tonic tensions elicited by longer depolarizing pulses was performed in bullfrog atrium under voltage-clamp conditions using the double sucrose gap technique. 2. 2. The experiments were done in the absence of Mn ions which are used to block slow inward current responsible for the generation of phasic tension. 3. 3. The differences of the sensitivity between the peak and terminal tonic tensions for various conditions (1. changes in temperature, 2. exposure to Ca-rich or Na-poor solution, 3. effects of conditioning pulses, 4. effects of ouabain and verapamil) were observed, suggesting that the nature of the terminal tonic tention is considerably different from that of peak tonic tension.