POTASSIUM RETENTION IN CRAB NERVE

Spectrophotometric determinations of the potassium content of small volumes of sea water brought into contact with crab nerves over half-hour intervals demonstrate (a) a continuous loss of potassium from the fibers while at rest in oxygen; (b) an appreciable increase in the leakage during anoxia; (c) a reabsorption of potassium during postanoxic recovery; and (d) a reduction in the amplitude of the anoxic and postanoxic changes in the presence of glucose

POTASSIUM MOVEMENT IN RELATION TO NERVE ACTIVITY

The depolarization of crab nerve during repetitive stimulation is unaffected by the presence of glucose or by an increase in the calcium content of the medium. It is increased in both amplitude and rate by veratrine; in the presence of this alkaloid mixture the rate but not the magnitude of the depolarization is increased by an elevation in the calcium concentration. Repolarization following stimulation is unaltered by glucose and accelerated by a greater calcium concentration. Veratrine increases both the amplitude and the time constant of repolarization; its effect on the time constant is counteracted by an elevation of the calcium in the medium. Potassium released during stimulation and its reabsorption following activity have been observed by analyses of small volumes of sea water in contact with crab nerve. Under the conditions employed 3 x 10–8 µM potassium is liberated per impulse per gm. wet weight of nerve. This loss is increased by low concentrations of veratrine, which also increase the amount reabsorbed during recovery. The depletion of potassium from the medium is appreciably less if the potassium previously released during activity has not been removed. Inexcitability resulting from anoxia can be washed away with oxygen-free solution—rapidly and completely in the case of the squid axon, slowly and incompletely in crab nerve. The potassium shifts are in the proper direction and of the correct order of magnitude to account for the negative and positive after-potentials in terms of potassium accumulation or depletion in the extracellular space

DRUG AND ION EFFECTS IN FROG MUSCLE

Procaine, cocaine, pyribenzamine, antistine, and phosphate decrease the uptake of water by frog sartorii in a Ringer solution in which potassium has been substituted for sodium; all but the last two leave the swelling in hypotonic Ringer practically unaltered. They also decrease the depolarizing action of potassium. These effects are considered indicative of reduced membrane permeability to potassium

ELECTRICAL PHENOMENA IN NERVE : II. CRAB NERVE

The resting and action potentials of the leg nerves of the spider crab are reduced by procaine, cocaine, iodoacetate, KCl, and veratrine. The first three agents depress the sensitivity of the resting potential to anoxia, while the last can be shown to augment it. Glucose sustains activity and the polarized state in the absence of oxygen, an effect blocked by iodoacetate; corresponding concentrations of lactate and pyruvate are inert under most experimental conditions. DDT and veratrine both induce repetitive activity following an impulse, but only the latter does so with a marked increase in negative after-potential. The negative after-potential induced by veratrine is decreased by KCl relatively more than the spike or the resting potential. Elevation of the calcium content of the medium increases this after-potential. Neither ion appreciably alters the time constant of repolarization. The recovery is more rapid than that obtained following prolonged activity of both veratrinized and unveratrinized nerves. Repolarization following a tetanus is accelerated by an increase in the volume of solution in contact with the fibers; associated with this is an augmentation of the positive after-potential which normally follows a bout of activity. Yohimbine induces a positive after-potential following individual spikes which is depressed by an elevation of the potassium or calcium content of the medium. These observations are discussed from the standpoint of the available evidence for the involvement of potassium at the surface of the fibers as regulated by a labile permeability and metabolism. The potassium liberated by the action potential, calculated from the polarization changes, agrees closely with an available analytical figure; less direct observations are also found to be consistent with this view

Calcium Flux and Contractility in Guinea Pig Atria

The calcium in guinea pig atria can be divided into three components by kinetic studies with Ca45: (a) a rapidly exchangeable fraction with a half-time of 4.5 minutes; (b) a slowly exchangeable fraction with a half-time of 86 (or 168) minutes; and (c) an inexchangeable fraction. In Krebs-Henseleit solution containing 2.5 mM calcium, the calcium content of the tissue at rest remains constant, the flux being about 0.02 µµmol/cm2-second. An increase or a decrease in extracellular calcium concentration by 1.25 mM causes a proportionate change in influx. A large increase in Ca45 entry, equivalent to as much as 0.55 µµ/mol/cm2 accompanies a contraction. When the strength of contraction is varied by stimulating at different frequencies or in solutions containing calcium at different concentrations, the increment of Ca45 uptake per beat changes proportionally with the strength of the beat. Total atrial calcium is not increased by stimulation; however, the increase in outflux of Ca45 during contraction that this constant tissue calcium implies could not be demonstrated under the experimental conditions employed. The observations are discussed in the light of the possible role of calcium transfer in excitation-contraction coupling

THE DISTRIBUTION AND KINETICS OF RELEASE OF RADIOCALCIUM IN TENDON AND SKELETAL MUSCLE

The distribution of Ca45 in frog (Rana pipiens) sartorius muscle, after 4 hours' exposure to Ringer's solution containing radiocalcium, has been analyzed by observing the kinetics of escape of the radioisotope into a non-radioactive Ringer's solution with calcium present or absent and by assuming that the tendon of Achilles is a satisfactory model of the extent of the uptake and release of Ca45 by the interstitial connective tissue (c.t.). In a Ringer's solution containing 1 mM/liter calcium, the exchangeable calcium distribution in micromoles per gram wet weight is as follows: (a) Aqueous phase of c.t. space: 0.16; (b) bound to c.t.: 0.16; (c) bound to surface of fibers: 0.13, of which 0.03 is displaced only by self-exchange, whereas the rest, as in c.t., can be displaced by other ions; and (d) in myoplasm: 0.33. The kinetics of Ca45 exit suggests that in infinite time of exposure to Ca45 the myoplasmic component would rise to 0.85. In the muscles, the half-time of the quickly emerging Ca45 averages about 3 minutes, whereas the time constant of the slowly released component is about 500 minutes. In the tendons the percentage rate of escape falls exponentially, the half-time of emergence being about 10 minutes

CALCIUM INFLUX IN SKELETAL MUSCLE AT REST, DURING ACTIVITY, AND DURING POTASSIUM CONTRACTURE

Calcium influx in the sartorius muscle of the frog (Rana pipiens) has been estimated from the rate of entry of Ca45. In the unstimulated preparation it is about equal to what has been reported for squid giant axons, but that per impulse is at least 30 times greater than in nerve fibers. The enhanced twitch when NO-2 replaces Cl- in Ringer's is associated with at least a 60 per cent increase in influx during activity, whereas this anion substitution does not affect the passive influx significantly. Calcium entry during potassium contracture is even more markedly augmented than during electrical stimulation, but only at the beginning of the contracture; thus, when a brief Ca45 exposure precedes excess K+ application, C45 uptake is increased three- to fivefold over the controls not subjected to K+, whereas when C45 and K+ are added together, no measurable increase in Ca45 uptake occurs. These findings are in keeping with the brevity of potassium contracture in "fast (twitch)" fibers such as in sartorius muscle

KINETICS OF ION MOVEMENT IN THE SQUID GIANT AXON

The loss of Na22, K42, and Cl36 from single giant axons of the squid, Loligo pealii, following exposure to an artificial sea water containing these radioisotopes, occurs in two stages, an initial rapid one followed by an exponential decline. The time constants of the latter stage for the 3 ion species are, respectively, 290, 200, and 175 minutes. The outflux of sodium is depressed while that of potassium is accelerated in the absence of oxygen; the emergence of potassium is slowed by cocaine, while that of sodium is unaffected. One cm. ends of the axons take up about twice as much radiosodium as the central segment; this difference in activity is largely preserved during exposure to inactive solution. Such marked differences are not observed with radiopotassium. From the experimental data estimates are given of the influxes and outfluxes of the individual ions. The kinetics of outflux suggests a cortical layer of measureable thickness which contains the ions in different proportions from those in the medium and which governs the rate of emergence of these ions from the axon as though it contained very few but large (relative to ion dimensions) pores

THE INFLUENCE OF HIGH HYDROSTATIC PRESSURE ON COCAINE AND VERATRINE ACTION IN A VERTEBRATE NERVE

The application of high hydrostatic pressure to toad sciatic nerve causes a gain in sodium and a loss of potassium which are not affected by cocaine. However, cocaine action is enhanced by high pressure when counteracting veratrine depolarization and when blocking the action potential. Various effects of elevated pressure on the after-potentials are presented and the role of ions in these processes is discussed

Radiocalcium Release by Stimulated and Potassium-Treated Sartorius Muscles of the Frog

Stimulation of frog (Rana pipiens) sartorius muscle accelerates release of Ca45, but only during the period of stimulation. No appreciable difference is obtained in the calcium released per impulse whether stimulation is at a rate of 20/sec. or 0.5/sec. However, prior stimulation may appreciably increase the loss per impulse. In unfatigued muscles, the minimum amount of calcium liberated during an isotonic twitch is estimated to be about that previously calculated to enter, viz. 0.2 µµmole/cm2. The time course of radiocalcium release during potassium depolarization depends on the nature of the contracture. When contracture is isometric, the rate of escape is doubled and declines only slowly; if isotonic, the rate is quadrupled but declines in a few minutes to a level maintained at about double that before potassium. The minimal calcium release during the first 10 minutes of potassium treatment is estimated to be about the same in both cases and about one-half to one-third the uptake. This, and especially the close equality of calcium entry and exit during electrical stimulation, are pointed out as not necessarily inconsistent with a transitory net entry of calcium, comparable to the influx, into restricted regions of the individual fibers