Abstract
Tropine p-tolylacetate (TPTA) and its quaternary analogue, tropine p-tolylacetate methiodide (TPTA MeI) decrease the early transient (Na) and late (K) currents in the voltage-clamped lobster giant axon. These agents, which block the nerve action potential, reduce the maximum Na and K conductance increases associated with membrane depolarization. They also slow the rate at which the sodium conductance is increased and shift the (normalized) membrane conductance vs. voltage curves in the direction of depolarization along the voltage axis. All these effects are qualitatively similar to those resulting from the action of procaine on the voltage-clamped axon. One unusual effect of the tropine esters, noticeable particularly at large depolarization steps, is that they cause the late, K current to reach a peak and then fall off with increasing pulse duration. This effect has not been reported to occur as a result of procaine action. Tropine p-chlorophenyl acetate (TPClφA), which differs from TPTA only by the substitution of a p-Cl for a p-CH3 group on the benzene ring, had a negligible effect on axonal excitability.
Full Text
The Full Text of this article is available as a PDF (550.3 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Blaustein M. P. Barbiturates block sodium and potassium conductance increases in voltage-clamped lobster axons. J Gen Physiol. 1968 Mar;51(3):293–307. doi: 10.1085/jgp.51.3.293. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Blaustein M. P., Goldman D. E. Action of anionic and cationic nerve-blocking agents: experiment and interpretation. Science. 1966 Jul 22;153(3734):429–432. doi: 10.1126/science.153.3734.429. [DOI] [PubMed] [Google Scholar]
- Blaustein M. P., Goldman D. E. Competitive action of calcium and procaine on lobster axon. A study of the mechanism of action of certain local anesthetics. J Gen Physiol. 1966 May;49(5):1043–1063. doi: 10.1085/jgp.49.5.1043. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Blaustein M. P., Goldman D. E. The action of certain polyvalent cations on the voltage-clamped lobster axon. J Gen Physiol. 1968 Mar;51(3):279–291. doi: 10.1085/jgp.51.3.279. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Blaustein M. P. Phospholipids as ion exchangers: implications for a possible role in biological membrane excitability and anesthesia. Biochim Biophys Acta. 1967 Sep 9;135(4):653–668. doi: 10.1016/0005-2736(67)90096-x. [DOI] [PubMed] [Google Scholar]
- DETTBARN W. D. The active form of local anesthetics. Biochim Biophys Acta. 1962 Feb 12;57:73–76. doi: 10.1016/0006-3002(62)91079-x. [DOI] [PubMed] [Google Scholar]
- Ehrenstein G., Gilbert D. L. Slow changes of potassium permeability in the squid giant axon. Biophys J. 1966 Sep;6(5):553–566. doi: 10.1016/S0006-3495(66)86677-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Friess S. L., Durant R. C., Martin H. L. Potency convergence and crossover in tertiary vs. quaternary tropine amino esters. Toxicol Appl Pharmacol. 1966 Sep;9(2):240–256. doi: 10.1016/0041-008x(66)90119-0. [DOI] [PubMed] [Google Scholar]
- ROSENBERG P., EHRENPREIS S. Reversible block of axonal conduction by curare after treatment with cobra venom. Biochem Pharmacol. 1961 Sep;8:192–206. doi: 10.1016/0006-2952(61)90002-8. [DOI] [PubMed] [Google Scholar]
- TAYLOR R. E. Effect of procaine on electrical properties of squid axon membrane. Am J Physiol. 1959 May;196(5):1071–1078. doi: 10.1152/ajplegacy.1959.196.5.1071. [DOI] [PubMed] [Google Scholar]