Effect of ouabain on potassium exchange in heart muscle mitochondria

Electrophysiology of an insect heart

Bioelectric activity in single cells of the moth myocardium has been measured in situ with intracellular microelectrodes with particular reference to the bizarre ionic medium which bathes the tissues. Resting potentials averaged 47 mv, inside negative with respect to outside, despite a value of 11 mv calculated on the basis of transmembrane potassium concentration gradients. Action potentials overshoot as much as 12 mv in the virtual absence of extracellular sodium. Two "types" of action potentials have been recorded; one that resembles vertebrate atrial action potentials is found in the cephalic region of the tubular heart, and the other, similar in contour to vertebrate ventricular action potentials, is found in the areas posterior to the first abdominal segment. Histological sections indicate no structural differences between the two areas. Typical cardiac pacemaker type potentials occur but are not topographically localized. The effects of the omission from the perfusion fluid of the four major cationic constituents, Na(+), K(+), Ca(++) and Mg(++), on resting and action potentials may be summarized as: no effect, hyperpolarization, prolonged repolarization, and depolarization, respectively.

Quantitative analysis of movements of potassium in rabbit auricles

When rabbit auricles are isolated in physiological saline solution at 29 or 37 °C, the influx or efflux of 42 K follows a course which can be described by the sum of two exponential terms. The presence of an initial fast component is more evident in beating than in spontaneously quiescent auricles, but the fast component is not due to beating because it occurs also in auricles in which beating is stopped by carbachol (2 x 10 -6 M). A small loss of potassium occurs in untreated auricles and a larger one under the influence of certain drugs, such as ouabain (10 -5 M) or dinitrophenol (10 -4 M). Several model systems are considered, especially those with three compartments all or partially communicating with each other, both with regard to exchange of tracer and to net changes in the total ionic content of the compartments. The simplest model which describes the observations had 79 ± 2 (S. E.) % of the tissue potassium free to exchange with the medium and the rest exchanging more slowly with the main fraction. In a steady state at 29 °C, in quiescent left auricles 1⋅07 % of the main fraction exchanged with the medium and 0⋅37 % with the slow fraction per minute. The corresponding rates for beating right auricles were 2⋅25 and 0⋅20 % per minute. In the presence of ouabain (10 -5 M) uptake from the medium to the main fraction was reduced to about 40% of the normal rate, with corresponding net loss of potassium. Dinitrophenol reduced or stopped uptake to the slow fraction and also accelerated loss from the main fraction to the medium.