ISSN:
1432-2013
Keywords:
Node of Ranvier
;
Block of Na channels
;
Procaine
;
Benzocaine
;
Procaine-benzocaine interaction
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract 1. Action potentials and their maximum rates of rise, $$\dot V_{\text{A}}$$ , were measured in single myelinated nerve fibres of the frog,Rana esculenta at room temperature. 2. On applying 1 mM procaine (pH 7.2) at 20 Hz stimulus frequency, half of the final $$\dot V_{\text{A}}$$ reduction was reached att on=0.27s; on applying 0.5 mM benzocaine (pH 7.2) at 50 Hz,t on was 0.12s. Increasing the stimulus frequency between 2 and 50 Hz increased the rate of block by procaine but not by benzocaine. 3. Recovery in Ringer solution (pH 7.2) from 30-s treatment with 1 mM procaine (pH 7.2), the equieffective 0.15 mM procaine (pH 8.9) and from 0.5 mM benzocaine (pH 7.2) was 54%, 31% and 70%, respectively, within 1 s. 4. Changing between alkaline Ringer solution (pH 8.9) and 1 mM procaine (pH 7.2) led to transitory excessive block. Changing between 1 mM procaine (pH 7.2) and acid Ringer solution (pH 6.0) and washing out 10 mM procaine (pH 5.5) with neutral Ringer solution also led to a non-monotonic change in $$\dot V_{\text{A}}$$ . 5. If hyperpolarizing pulses (30 ms, 20 mV) preceded the stimuli, changing the frequency of the pulse pairs led to a gradual moderate relief of block in procaine, turning off prepulses (at 10 Hz) to a gradual increase of block. In benzocaine changing from 1 to 10 Hz had no effect but turning off prepulses led to a prompt large increase of block. In procaine + benzocaine the membrane responded much as in benzocaine alone. At 1 Hz (prepulses) $$\dot V_{\text{A}}$$ in 0.4 mM procaine wassmaller than in 0.4 mM procaine + 0.3 mM benzocaine. 6. These phenomena can be explained on the assumption of voltage-dependent binding of benzocaine and procaine to a common receptor. The rate of block appears to be limited by access to the receptor, more in the case of benzocaine than of procaine.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00581574
