Movements of potassium in rabbit auricles

Acetylcholine and potassium-42 movements in right atrial muscle of the guinea pig

The effect of acetylcholine (ACh) on potassium (K-42) movements has been studied in right atrial tissue of the guinea pig. When quiescent fibers were stimulated at 108 beats/min, potassium uptake was increased to a small but significant extent. Administration of acetylcholine (2.7 X 10(-6) M) induced an increase in potassium uptake that was greater in fibers that were quiescent than in the same fibers when stimulated. The ACh induced increase in potassium uptake was abolished by atropine (5.2 X 10(-7) M) and enhanced in the presence of nicotine (10(-5) M). In addition, ACh induced an increase in potassium efflux that was greater in fibers that were quiescent than in the same fibers when stimulated. Atropine blocked the effect of ACh on potassium efflux. It is concluded that activity of atrial tissue increases potassium uptake and modifies the action of ACh on potassium uptake and efflux. Muscarinic receptors mediate the ACh induced increase in potassium movements. Nicotinic receptors may mediate an ACh induced decrease in potassium uptake in atrial muscle.

Potassium in Dog Ventricular Muscle: Kinetic Studies of Distribution and Effects of Varying Frequency of Contraction and Potassium Concentration of Perfusate

Four phases (0 to 3) were defined kinetically for potassium in the dog papillary muscle when perfused arterially for four to five hours with solution containing 4 mM/liter K + . Total tissue K + fell from 91.1±1.99 to 41.0±1.06 mmoles/liter after three hours perfusion. It then remained stable during the period when kinetic studies were done. The mean rate constant λ (min -1 ), potassium content (mmoles/liter tissue water) and suggested origin of each phase are respectively: (phase 0) λ 0 = 3.2, 0.3, vascular; (phase 1) λ 1 = 0.65, 2.06, interstitial; (phase 2) λ 2 = 0.0139, 39.3, intracellular; (phase 3) λ 3 < 0.004, <0.5, origin unknown.

Alteration of K + concentration in perfusing fluid produced significant changes in the intracellular exchange rate of K + . This was in marked contrast to increments in frequency of contraction which had no effect on the overall exchangeability of intracellular potassium. Increases in rate, however, were associated with a transient net loss of intracellular K + . This loss continued if the active tension of the muscle declined and if contracture progressed. The loss ceased if muscle function remained stable during continued increased frequency of contraction. A positive tension staircase was approximately proportional to the net K + loss. The net K + loss was 0.93 mmole/liter tissue water in nine muscles in which a mean 27 beats/min rate increment was introduced for a mean of 16 minutes. This represented 2.4% of intracellular K + .

A significant time lag was found before the net K + loss reached a maximum rate and began to decline. This is compared with the previously demonstrated transient net increment in Ca ++ uptake that accompanies increased frequency of contraction. These ionic movements are consistent with the theory that Na + movements in and out of a "specialized membrane region" are related to Ca ++ movements and thereby influence the control of myocardial contractility.

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.