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R I Macey

Publications and source records attributed to R I Macey.

52 records · Page 3Linked to original sources
PubMed1969

The N-shaped current-potential characteristic in frog skin. I. Time development during step voltage clamp.

A fast (10 musec) voltage-clamp system similar to that used on nerve axons was applied across the frog skin. An electrical analog is used to obtain the electrical parameters and to estimate the time (300 musec) required to voltage clamp the excitable membrane layer in the skin. The speed of the clamp allows observation of the early development in time of an N-shaped current-potential (I-V) relation. The isochronal I-V curves constructed from step clamp data show the beginning of a negative slope in about 250 musec after successively applied step changes in skin potential (> 200 mv). Subsequently, the negative slope reaches a quasi-steady state interval (0.4-1.5 msec) and then decays and disappears in the next 20 msec. The negative slope I-V characteristic is only found in skins which exhibit spike generation under current clamp.

Animals↗
PubMed1969

The N-shaped current-potential characteristic in frog skin. II. Kinetic behavior during ramp voltage clamp.

Previous step voltage-clamp measurements on frog skin showed the presence of an N-shaped current-potential (I-V) relation in excitable skin. However, the collection and reconstruction of I-V data using discrete step changes of skin potential was tedious because of the long refractory period (up to 1 min) in frog skin. A direct and rapid (5 msec) method for recording the N-shaped I-V characteristic in real time is presented. Ramp functions are used as the command to the clamp system instead of a step function. Consequently the skin potential is forced to change in a linear manner (as commanded) and the skin current can be recorded as a continuous function of the controlled change of skin potential. With the ramp clamp, a low-resistance membrane state ( 10 Omega . cm(2)) resembling a breakdown phenomenon was observed at high skin potential ( 300 mv). Entry into the low resistance state resulted in a collapse of the N-shaped I-V relation to a nearly linear function. The utility of the ramp measurement is demonstrated by predicting (1) that the maximum rate of rise of the spike occurs at a voltage corresponding to the valley (local minimum) in the N-shaped I-V curve, (2) that the rate of rise of the spike increases with increasing clamp currents, (3) the voltage peak of the spike, and (4) the time course of the rising phase of the spike.

Animals↗
PubMed1969

The N-shaped current-potential characteristic in frog skin. 3. Ionic dependence.

A ramp voltage clamp measurement described previously is used to detect alterations in the frog skin current-potential (I-V) characteristic following removal or replacement of various ions in the solutions bathing the skin. The ionic requirements for the maintenance of a negative-slope I-V property are the following: Ca(++), Na(+), and Cl(-) must be in the outside solution; K(+) and Cl(-) must be in the inside solution. Removal of any one of these ions from its respective solution results in the decay and eventual disappearance of the negative slope.The similarity between the I-V characteristic following Ca(++) removal with EDTA from the outside solution and the I-V relation in a refractory skin suggests that the loss (refractory state) and recovery of the negative slope is a consequence of unbinding and subsequent rebinding of Ca(++) to membrane sites. The role of the univalent ions is not clear-presumably some or all of these ions constitute the current through the skin; however, some of these ions may also be involved in maintaining a membrane condition necessary for the existence of a negative slope I-V relation. Further, excitation does not appear to be a direct consequence of the Na(+) pump.

Animals↗
PubMed1967

The time dependence of single file diffusion.

The single file diffusion of particles through a narrow pore membrane separating two media is treated as a stochastic birth and death process. A set of differential-difference equations is derived to describe the probability of finding n particles in the pore at any time whose source is the left-hand medium. Explicit time-dependent solutions for an arbitary number of sites are obtained. These can be used to calculate both one-way and net flux as a function of time. Parameters are estimated from steady state permeability data, and the results of some numerical calculations are presented to illustrate the time required to approach a steady state. In many cases, significant time delays can occur.

Mathematics↗