Current-voltage relations in ventricular muscle preparations from different species.

Current-voltage relations were determined in ventricular muscle preparations from dog, sheep, pig, guinea pig, bull and cat hearts. The single sucrose gap voltage clamp method was used to apply 2 s steps or slow speed voltage ramps (3-4 mV/s). 1. The current-voltage relations obtained with 2 s steps were similar to those obtained with ramps. 2. Negative slope regions were readily apparent in the current-voltage relations of preparations from all species except cat although the latter did display marked anomalous rectification. 3. Increasing the external potassium concentration from 3 to 10 mM increased the slope of the current-voltage relation around the resting potential and resulted in the "crossing-over" and "crossing-back" of the relations if all tissues. 4. The two extreme cases of bull (marked negative slope region) and cat (no negative slope region) were compared with regard to transgap intracellular and extracellular resistances; they were quite similar. This suggests that the current-voltage relations reflect differences in membrane properties rather than, for example, different proportions of non-membrane leakage current. 5. In bull ventricular preparations, the application of D-600 (2 X 10(-6) M), 30 min) had only a small effect on the current-voltage relation. In contrast, cesium (10-20 mM) nearly abolished the negative slope region suggesting that this characteristic of the current-voltage relation is due to potassium channel rectification. 6. Possible explanations for action potential durations in bull ventricular fibres being 50 to 100% longer than in cat are considered.