Quantitative analysis of movements of potassium in rabbit auricles

Adrenaline, anti-adrenaline drugs and potassium movements in rabbits auricles

Adrenaline (2x10(-6) M) or isoprenaline (7.5x10(-8) M) increased the rate of (42)K uptake and the potassium content of right (spontaneously beating) auricles, but had no effect on potassium movements in quiescent left auricles. Although faster beating induced by electrical stimulation increased the rate of (42)K uptake, the actions of adrenaline were also apparent in auricles which were electrically stimulated so that they beat at a constant rate. The increase in (42)K uptake produced by adrenaline accounted entirely for the increase in potassium content of the tissue. Adrenaline, in concentrations ranging from 2x10(-6) M to 2x10(-4) M, had no effect on (42)K loss from electrically stimulated auricles. The action of adrenaline on (42)K uptake was blocked by dichloroisoprenaline (4x10(-6) M) but not by phenoxybenzamine (1.6x10(-6) M).

Comparison of myocardial potassium and thallium flux as studied by tracer methods

Although myocardial scintigraphy with 201thallium is widely applied in humans, the behavior of thallium at the cellular level is still under discussion. We compared the transmembrane fluxes of potassium and thallium in the isolated papillary muscle of guinea pigs. A qualitative conformity exists between potassium and thallium fluxes with respect to heart rate and temperature. Quantative comparison revealed a decreased flux rate of thallium for efflux when compared with potassium. The time dependence of thallium influx indicates that thallium scintigraphy of the myocardium reflects mainly an extracellular distribution.

Permeation and distribution of deuterated and tritiated water in smooth and striated muscle

1. The diffusion of deuterated water (HDO) into and out of isolated guinea-pig taenia coli and frog sartorius was followed by means of a recording electronic microbalance.2. A comparison was made of the rates of efflux of deuterated and tritiated (HTO) water using the microbalance and a standard tracer technique.3. The time course of the exchange of HDO in both smooth and striated muscle was fitted to the sum of two exponential functions; however, it was not possible to correlate sizes of the intra- and extracellular spaces in the muscles with the sizes of the two compartments in model systems based on compartmental theory of tracer kinetics.4. The efflux of HDO, which was measured by means of the microbalance under stagnant conditions, occurred at a rate approximately 3 times slower than the efflux of HTO which took place while muscles were agitated vigorously in their bathing media.5. There was a marked deviation at short times from a double exponential time course during the efflux of HTO.6. Values of the tracer water permeability, P(d), of smooth and striated muscle fibres, and the extracellular space, E, of the muscles were obtained using a computer to numerically evaluate the series solutions of the equations describing the permeation of labelled water in the muscles.7. It was necessary to assume a value for the diffusion coefficient of the tracer in extracellular fluid in order to compute a unique fit to an exchange curve.8. Values of P(d) and E given by the analysis depended upon the method used for monitoring the exchange, and an interpretation of this dependence was made difficult by the variation in the thickness of unstirred layers on the surface of the muscles under the different experimental conditions.

Interaction of 28Mg with Ca and K in the smooth muscle of guinea-pig taenia coli

1. The uptake of (28)Mg, and the total tissue content of Mg, Ca, Na and K have been determined in the smooth muscle of the guinea-pig taenia coli. The Mg content was 6.56 m-mole/kg fresh wt. immediately after dissection, falling slowly to 5.11 after 6 hr immersion in Krebs solution at 37 degrees C.2. The Mg content rose to 15.4 m-mole/kg fresh wt. during immersion in isotonic sucrose containing only MgCl(2). It was independent of the Mg(2+) concentration in this solution, but was depressed when K(+) or Ca(2+) ions were added.3. (28)Mg uptake showed three separate phases, extracellular, intermediate and slow. The size of the extracellular phase was proportional to the Mg(2+) concentration in the solution, but the size of the slow phase was constant. The size of the intermediate phase, exchanging with a half-time of a few minutes, was depressed when K(+) or Ca(2+) ions were added.4. The results are compatible with a competition between Mg in the intermediate phase of tracer exchange, and K(+) or Ca(2+) ions for fixed anionic sites in the tissue.

The calcium content of the smooth muscle of the guinea-pig taenia coli

1. The in vitro calcium content of the smooth muscle of the guinea-pig taenia coli was 3.0 m-mole Ca/kg wet wt. when phosphate was omitted from the bathing medium, and was almost independent of pH changes in the range 6.7-7.6.2. The calcium content was not changed when 1 mM phosphate was included in the medium, if the pH was 6.7 or 7.0. However, when the pH was 7.6, the calcium content increased by 1.5 m-mole Ca/kg wet wt. in the presence of phosphate.3. The calcium content rose by 1.1 m-mole Ca/kg wet wt. when NaCl in the bathing medium was replaced by isotonic sucrose, and rose by 0.7 m-mole Ca/kg wet wt. when MgCl(2) in the bathing medium was replaced. These increases may reflect a competition between Ca(2+) and other cations for fixed negative sites in the tissue.4. The initial rapid phase of (42)K exchange corresponded to an ;extra-cellular (42)K-space' of 470 ml./kg fresh wt. in normal solution, rising to 560 ml./kg. fresh wt. in low-sodium solution and to 760 ml./kg fresh wt. in calcium-free low-sodium solution. In this last medium the extra-cellular [(14)C]sorbitol space was only 390 ml./kg fresh wt., so that there was a large excess of rapidly-exchanging potassium which may have been competing at fixed negative sites.

An interaction between potassium and sodium in the smooth muscle of the guinea-pig taenia coli

1. The potassium content of the guinea-pig taenia coli was 72 m-mole K/kg fr. wt. after equilibration with normal Krebs-type solution at 35 degrees C in vitro.2. It fell to 13 m-mole K/kg fr. wt. when Ca(2+) and Mg(2+) were omitted from the bathing solution, but this fall was reversed in part when [Na(+)](o) was also reduced.3. The taeniae relaxed when Ca(2+) and Mg(2+) were omitted from the normal solution. However, they contracted if Na(+) was also omitted.4. Effects 2 and 3 may show some antagonism between sodium and divalent cations in smooth muscle.5. The extracellular space of the same muscles was measured with [(14)C]sorbitol. It was 440 ml./kg fr. wt. in normal solution.6. The uptake of (42)K was measured in the same muscles at the same time. An initial rapid exchange was followed within 2 min by a slow (half-time [unk] 50 min in normal solution) and presumably intracellular uptake of tracer.7. In normal solution the initial rapid phase of (42)K exchange corresponded to 3.0 m-mole K/kg fr. wt. A value of 2.6 m-mole K/kg fr. wt. would have been calculated from [K(+)](o) and the [(14)C]sorbitol space, and these estimates did not differ significantly.8. The [(14)C]sorbitol space fell slightly when [Ca(2+)](o), [Mg(2+)](o), and [Na(+)](o) were reduced, but the amount of rapidly exchanging potassium increased significantly reaching 4.6 m-mole K/kg fr. wt. in solutions from which Ca(2+), Mg(2+) and Na(+) were omitted. The [(14)C]sorbitol space only accounted for 2.4 m-mole K/kg fr. wt. under these conditions, a significantly smaller quantity.9. The observations have been interpreted on Wilbrandt & Koller's (1948) hypothesis that there may be a superficial anionic region in muscle cells. On this model the present results suggest that K(+) rather than Na(+) is favoured as a monovalent counter-cation in the taenia coli.

Ions and the action of digitalis

Images