. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. B OmV- 4uA 40 mV -200 -150 -100 - 2ms V. IOiA) 50 100 150 200 V(mV) Figure 6. Direct resistance measurements. (A) Schematic of experimental setup. A defined length of axon was placed on a clear plastic platform, and each end was cut and placed in a bath containing internal solution (in mM: 500 K-glutamate, 10 HEPES, EGTA, pH ). The interbath voltage was clamped using a home-built squid axon apparatus, and the resulting current was measured. (B) An example of the current resulting from a 100-mV voltage step (May
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. B OmV- 4uA 40 mV -200 -150 -100 - 2ms V. IOiA) 50 100 150 200 V(mV) Figure 6. Direct resistance measurements. (A) Schematic of experimental setup. A defined length of axon was placed on a clear plastic platform, and each end was cut and placed in a bath containing internal solution (in mM: 500 K-glutamate, 10 HEPES, EGTA, pH ). The interbath voltage was clamped using a home-built squid axon apparatus, and the resulting current was measured. (B) An example of the current resulting from a 100-mV voltage step (May axon). (C) Current-voltage relationship from the same axon. All experiments performed at temperatures between 18° and 20°C. the action potential in May squid is over twice as long as it is in August squid (see Fig. 1 for examples of action potentials recorded at 10°C and 20°C). Unlike the action potential duration, the conduction velocity does appear to be regulated between seasons. However, the direction of the change is not consistent with a compensatory thermal ac- climation: despite a seasonal disparity in axon diameter, the relationship between conduction velocity and temperature remains constant, due mostly to resistive changes in the axon. Computer simulations of conduction velocities using the Hodgkin and Huxley equations (Hodgkin and Huxley, 1952) support this assertion. By substituting the May and August values for Cm(/?; + /?,.). determined by tits to the action potential foots ( OF and flF, respectively, at 10°C), there is a increase in conduction velocity. The difference determined from direct measurements of conduc- tion velocities in May and August axons at 10°C was Fits to the action potential foot predicted that the product of (/?,. + Re) and C,,, increased by approximately 30% between August and May. This is in reasonable agreement with direct measurements of (/?,- + /?t,) for the same sea- sons, which increased by 22%. Capacitive c
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
