Abstract
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 Ω · cm2) 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.
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Selected References
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- ALTAMIRANO M., COATES C. W., GRUNDFEST H. Mechanisms of direct and neural excitability in electroplaques of electric eel. J Gen Physiol. 1955 Jan 20;38(3):319–360. doi: 10.1085/jgp.38.3.319. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bennett M. V., Grundfest H. Analysis of depolarizing and hyperpolarizing inactivation responses in gymnotid electroplaques. J Gen Physiol. 1966 Sep;50(1):141–169. doi: 10.1085/jgp.50.1.141. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Coster H. G. A quantitative analysis of the voltage-current relationships of fixed charge membranes and the associated property of "punch-through". Biophys J. 1965 Sep;5(5):669–686. doi: 10.1016/S0006-3495(65)86745-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- DECK K. A. Uber die Wirkung des Guanidinhydrochlorids und anderer Substanzen auf das Aktionspotential der Nerveneinzelfaser. Pflugers Arch. 1958;266(3):249–265. doi: 10.1007/BF00416776. [DOI] [PubMed] [Google Scholar]
- FINKELSTEIN A. ELECTRICAL EXCITABILITY OF ISOLATED FROG SKIN AND TOAD BLADDER. J Gen Physiol. 1964 Jan;47:545–565. doi: 10.1085/jgp.47.3.545. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Fishman H. M., Macey R. I. The N-shaped current-potential characteristic in frog skin. I. Time development during step voltage clamp. Biophys J. 1969 Feb;9(2):127–139. doi: 10.1016/S0006-3495(69)86374-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- JULIAN F. J., MOORE J. W., GOLDMAN D. E. Current-voltage relations in the lobster giant axon membrane under voltage clamp conditions. J Gen Physiol. 1962 Jul;45:1217–1238. doi: 10.1085/jgp.45.6.1217. [DOI] [PMC free article] [PubMed] [Google Scholar]
- MUELLER P. Effects of external currents on duration and amplitude of normal and prolonged action potentials from single nodes of Ranvier. J Gen Physiol. 1958 Sep 20;42(1):163–191. doi: 10.1085/jgp.42.1.163. [DOI] [PMC free article] [PubMed] [Google Scholar]
- RUDOLPH G., STAMPFLI R. Anodenöffnungserregungen einzelner Ranvier-Schnürringe. Pflugers Arch. 1958;267(5):524–531. doi: 10.1007/BF00361739. [DOI] [PubMed] [Google Scholar]
- WERMAN R., McCANN F. V., GRUNDFEST H. Graded and all-or-none electrogenesis in arthropod muscle. I. The effects of alkali-earth cations on the neuromuscular system of Romalea microptera. J Gen Physiol. 1961 May;44:979–995. doi: 10.1085/jgp.44.5.979. [DOI] [PMC free article] [PubMed] [Google Scholar]