Digoxin, Ouabain and Potassium Movements in Rabbit Auricles

Abstract

Movements of potassium have been observed in isolated right and left auricles of rabbits by means of radioactive tracer. The tissues have been immersed in a modified Krebs saline at 370, and in these conditions showed only small changes in ionic content over periods up to 6 hr.The extracellular volume, determined with inulin and with 2"Na, was large (44.1 ml./100 g. tissue), and accounted for about 3.8% of the tissue potassium. Left auricles exchanged without gross inhomogeneity: the rate of exchange was about 1.5% of the total tissue potassium/min., though it was probably higher in the first half-hour or hour after preparation. In right auricles the exchange was less homogeneous and included a faster component than that observed in left auricles. Digoxin and ouabain reduced the influx and had no appreciable effect on the efflux of potassium, so that the auricles lost potassium. The threshold concentrations which produced effects within 20 min. were of the order of 10-6 for ouabain and somewhat higher for digoxin. Irregularities or failure of contraction occurred when the tissue potassium was reduced by about 15%. Loss of potassium was accompanied by gain of sodium, but the tissue appeared unsuitable for making estimations of the rate of sodium movement.

Adrenaline, Anti‐adrenaline Drugs and Potassium Movements in Rabbit Auricles

“…Rabbit auricles were used because much is known about their normal potassium exchanges and the effects of drugs upon them (Rayner & Weatherall, 1957, 1959Persoff, 1960;Waddell, 1961;Weatherall, 1962). Small rabbits (<1.5 kg) were killed by a blow on the head and the heart removed rapidly.…”

Acetylcholine and potassium movements in rabbit auricles

“…The fast part is not due to the anatomical pacemaker, as we previously suggested (Rayner & Weatherall, 1957), because a similar fraction appears in left auricles when they are driven electrically. Earlier experiments (Rayner & Weatherall, 1957 , Table 3) suggested that there was no fast uptake by left auricles which were beating in undivided pairs, but the results could have been vitiated by inadequate allowance for the effects of cutting the bridge of tissue between the two auricles.…”

“…The fast part is not due to the anatomical pacemaker, as we previously suggested (Rayner & Weatherall, 1957), because a similar fraction appears in left auricles when they are driven electrically. Earlier experiments (Rayner & Weatherall, 1957 , Table 3) suggested that there was no fast uptake by left auricles which were beating in undivided pairs, but the results could have been vitiated by inadequate allowance for the effects of cutting the bridge of tissue between the two auricles. If it is assumed that exchange of a little potassium (2-4 %) of each auricle is accelerated by such a cut (as it may be by end effects and increased surface area) the typical difference between active and inactive tissue is apparent and the previously unexplained discrepancy in the faster uptake of separated than undivided right auricles is accounted for.…”

“…Application of the procedure, including esti- mates of necessary tissue dimensions and correction for diffusion (Keynes, 1954), has been described previously (Rayner & Weatherall, 1957) and need not be repeated. The potassium concentrations of the auricles at the ends of the experiments, whether treated with drugs or not, were within the range observed for fresh auricles (Rayner & Weatherall, 1957), and no adjustment has been made for the small losses of potassium which probably occurred.…”

“…Estimates based on net changes in the composition of the tissue in special circumstances (Holland, 1954(Holland, , 1957 are well known not to give a measure of the total influx and efflux, and even estimates with the use of tracer are subject to limitations particularly obvious in beating tissues in which the fluxes are probably different at different stages of each contractile cycle. Rayner & Weatherall (1957) estimated that the potassium influx and efflux of isolated quiescent left auricles were about 5-8 pmole/cm2. sec, and showed that part of the tissue potassium of right auricles exchanged more rapidly.…”