Echinococcus granulosus: characterization of the electrical potential of the syncytial tegument of protoscoleces incubated in vitro--effect of inhibitors.
Upon microelectrode impalements of the tegument of Echinococcus granulosus protoscoleces incubated in Ringer Krebs solution, electrical potential differences of -49 +/- 1 mV, using procedure I, and -53 +/- 1 mV, using procedure II, were recorded. The changes in the electrical potential difference as well as the structural alterations produced by sodium deoxicholate indicate that the observed potentials are established across the apical membrane of the syncytial tegument. The electrical potential difference is primarily dependent on the K+ gradient across the tegumental membrane: a 10-fold increase in the external K+ causes a 30-mV change in the electrical potential. External Na+ concentration changes also affected the electrical potential difference, but altering the external Cl- has no detectable effect. Amiloride, a very well-known blocker of Na+ epithelia channels, produced a reversible hyperpolarization that reached the maximum response at 10(-3) M. Ouabain, 10(-4) M, caused a depolarization in both fresh and Na-rich protoscoleces, although this depolarization was greater and showed a faster onset under the latter condition. It is concluded that the electrical potential difference of E. granulosus protoscolex is generated at the apical tegumental membrane and that it can be experimentally divided into two main components: One of them depends on ionic gradients and membrane permeabilities in accordance with the electrodiffusion predicted by the Goldman, Hodgkin, and Katz equation, while the other depends on the electrogenicity of an active Na+/K+ transport system.
Ibarra
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Departamento de Biofísica, Fundación CIMAE, Buenos Aires, Argentina.
Reisin
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IL
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002712:Chlorides / Q000494:pharmacology; D003840:Deoxycholic Acid / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004446:Echinococcus / Q000187:drug effects / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D008564:Membrane Potentials; D008839:Microelectrodes; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology
D002712:Chlorides; D003840:Deoxycholic Acid; D010042:Ouabain; D000584:Amiloride; D012964:Sodium; D011188:Potassium