Biomedical subjects

E B Ridgway

Publications and source records attributed to E B Ridgway.

6 recordsLinked to original sources

PubMed1978

Calcium transients and relaxation in single muscle fibers.

Muscle contraction is initiated by an elevation in intracellular calcium. The transient change in free calcium to a brief depolarization, the calcium transient, can be recorded using a calcium luminescent protein, aequorin. The calcium transient precedes force, peaking while force is rising and returning to the resting level as peak force is achieved. In single barnacle muscle fibers microinjected with aequorin, shortening the muscle during the declining phase of the calcium transient produces an addition light signal, indicating extra free calcium in the sarcoplasm. The amount of additional light is larger with larger length changes. It is also larger if the shortening occurs early in the calcium transient rather than later. The amount of this extra calcium correlates well with the instantaneous level of the calcium transient and not with the instantaneous force level. It is argued in a speculative manner that this extra calcium is coming from the myofilaments. This supports the hypothesis that calcium binding to the myofilaments is rapid and reversible, that reaccumulation of calcium into the sarcoplasmic reticulum (SR) could occur long before relaxation begins and that relaxation of tension could occur by some process other than the mere removal of calcium from the myofilaments.

Aequorin↗

PubMed1977

Free calcium increases explosively in activating medaka eggs.

We have used the calcium-specific light-emitting protein aequorin to follow changes in free calcium concentration during fertilization and cleavage of eggs from medaka, a fresh-water fish. Aequorin-injected medaka eggs show a very low resting glow before they are fertilized, indicating a low calcium concentration in the resting state. Upon activation by sperm, the calcium-mediated light emission increases to a level some 10,000 times the resting level with a 1 to 2 sec time constant for an e-fold increase, and then slowly retruns to the resting level. Upon activation by the ionophore A23187, the early rise in luminescence is much slower, but once a threshold has been reached the subsequent rise becomes as rapid as the normal sperm-induced response. We infer that the explosive rise in calcium involves calcium-stimulated calcium release, and that a sperm normally triggers this rise by somehow inducing a more modest and localized rise in calcium.

Aequorin↗

PubMed1977

Voltage-dependent facilitation of Ca2+ entry in voltage-clamped, aequorin-injected molluscan neurons.

Voltage-clamp experiments were performed on giant neurons of the nudibranch Anisodoris nobilis injected with the Ca-sensitive photoprotein, aequorin. Depolarization beyond -10 to +5 m V produced an aequorin signal, the amplitude of which depended on the extracellular Ca2+ concentration, the amplitude of the depolarization, and its duration. In paired pulse experiments, the amplitude of the aequorin signal produced in response to the second of two identical depolarizing pulses was larger than that produced during the first, resulting from an increased entry of Ca2+ during the second pulse. The increment in Ca conductance inferred from the augmented signal during the second pulse was independent of Ca2+ influx during the first pulse but, instead, was related to the amplitude and duration of the first pulse.

Aequorin↗

PubMed1976

Control of chemotaxis in Physarum polycephalum.

Plasmodia migrate towards those situations which increase the frequency of their alternations in streaming, and away from those which decrease the frequency. Therefore peristalsis-like waves in Physarum move in the direction opposite from the net movement of the organism. The mechanism is fundamentally related to other known types of chemotaxis.

Chemotaxis↗

PubMed1976

Oscillations of calcium ion concentrations in Physarum polycephalum.

Aequorin is a photoprotein which emits light in response to changes in free calcium concentration. When aequorin was microinjected into plasmodia of Physarum polycephalum, light emission varied in synchrony with the motile oscillations of the organisms. Therefore, movement is correlated which changes in the concentration of free calcium.

Aequorin↗

PubMed1976

Length-dependent electromechanical coupling in single muscle fibers.

In single muscle fibers from the giant barnacle, a small decrease in muscle length decreases both the calcium activation and the peak isometric tension produced by a constant current stimulus. The effect is most pronounced if the length change immediately precedes the stimulation. In some cases, the decrease in tension with shortening can be accounted for almost entirely by a decrease in calcium release rather than changes in mechanical factors such as filament geometry. During the constant current stimulation the muscle membrane becomes more depolarized at longer muscle lengths than at the shorter muscle lengths. Under voltage clamp conditions, when the membrane potential is kept constant during stimulation, there is little length dependence of calcium release. Thus, the effect of length on calcium release is mediated through a change in membrane properties, rather than an effect on a subsequent step in excitation-contraction coupling. Stretch causes the unstimulated fiber membrane to depolarize by about l mV while release causes the fiber membrane to hyperpolarize by about the same amount. The process causing this change in potential has an equilibrium potential nearly 10 mV hyperpolarized from the resting level. This change in resting membrane potential with length may account for the length dependence of calcium release.

Animals↗