The Efflux of Substances from Frog Ventricles to Sucrose and to Ringer's Solutions

Abstract

The frog ventricle in sucrose solution contracts for several hours at 25°C, and for as long as 24 hours at 50°C. The possibility that a fraction of the extracellular fluid remains outside of the excitable membrane was examined by measuring the efflux of tracers. The half-time for the efflux to sucrose solution at 25 0 C of C 4 sucrose is about 1 minute, for Na 24 is 6.5 minutes, and for C18 is 4 minutes. There is no evidence for the retention of an extracellular Na fraction. The Qo for Na and C1 effiux is about 1.3. The half-time for K42 efflux is about 180 minutes; the Q,0 is 1.7. The effiux rates of Na 2 4 , C136, and K 42 to sucrose and to Ringer's solutions are quite similar. Ca" 4 efflux is only one-fifth as fast to sucrose solution as to Ringer's; the retention of Ca + + may be important for maintaining excitability in sucrose solution. P efflux is five times faster to sucrose solution than to Ringer's solution, and there is a similar increase in the rate of inosine loss to sucrose solution. The Qo for efflux to sucrose solution is 2.2 for P20 4 and 2.4 for inosine. We suggest that energy metabolism is abnormal in ventricles in sucrose solution and that low temperature prolongs excitability by slowing the metabolic change.A frog heart immersed in isotonic sucrose solution continues to conduct action potentials and to contract for several hours (Singh, Sehra, and Singh, 1945;Singh, 1962;Van der Kloot and Rubin, 1962). This observation raises obvious difficulties for ideas about the inflow of Na + generating the action potential, and about the inflow of Ca + + triggering contraction. The simplest explanation would be that as long as the muscle remains active the sucrose solution does not completely replace the extracellular fluid. This possibility is now examined by measuring the ion contents of sucrose-soaked ventricles and the kinetics of the efflux of radioactive ions and certain other substances from cardiac muscles into sucrose and Ringer's solutions.A second observation was also kept in mind when designing the experiments.

Differential Effects of Ouabain and 2,4‐dinitrophenol on Contractile Tension of and on Sodium and Calcium Efflux From Frog Heart Ventricular Strips

“…Probably, k1 also represents washout from the extracellular space, and k1l from a cellular compartment. These results with sodium and calcium efflux resemble those of Van der Kloot & Dane (1964), who used whole frog ventricles, except that calcium efflux was somewhat slower in the present experiments.…”

“…105 min-'), is generally interpreted as washout from the extracellular space, a compartment that represents about 20% of the tissue fluid, and from which substances diffuse with comparable kinetics to those of this efflux component (Winegrad & Shanes, 1962; Van der Kloot & Dane, 1964;LundAndersen, 1974 where they were stimulated at 0.2 Hz, and where the incubation fluid was renewed with non-radioactive Ringer every 2 min. Radioactivity remaining in the tissue, expressed as % of the initial (log scale)!…”

“…The second kinetic component (Tt = 6.6 min; kl1:0. 105 min-'), is generally interpreted as washout from the extracellular space, a compartment that represents about 20% of the tissue fluid, and from which substances diffuse with comparable kinetics to those of this efflux component (Winegrad & Shanes, 1962; Van der Kloot & Dane, 1964;Lund-Andersen, 1974). A third, much slower kinetic component (TI =38 min; k11:0.0182 min-1), possibly where they were stimulated at 0.2 Hz, and where the incubation fluid was renewed with non-radioactive Ringer every 2 min.…”

The dependence of calcium efflux from cardiac muscle on temperature and external ion composition

“…The transient peak in efflux curves which could be observed in our experiments when Ca or Na were first readmitted to the preparation after a period in Ca-free solution or Na-free sucrose solution could be explained as ion exchange at superficial sites, since it depended only on the presence of a certain minimal ion concentration and not on a special cation (cf. van der Kloot & Dane, 1964). Such a non-specific cation exchange, however, cannot explain the high specificity of the Na-activated fraction of Ca efflux for Na.…”

“…In this case, Na and inactive Ca would exchange for 45Ca at the surface binding sites without influencing intracellular Ca-concentration. Evidence for extracellular binding of Ca has been presented for skeletal muscle and tendons (Bianchi & Shanes, 1960) for smooth muscle (Bauer, Goodford & Hiiter, 1965) and for cardiac muscle (Niedergerke, 1963 a, b;van der Kloot & Dane, 1964). The transient peak in efflux curves which could be observed in our experiments when Ca or Na were first readmitted to the preparation after a period in Ca-free solution or Na-free sucrose solution could be explained as ion exchange at superficial sites, since it depended only on the presence of a certain minimal ion concentration and not on a special cation (cf.…”