Permethrin mimics the action of DDT on adult rat brain neurolemma microtransplanted into Xenopus laevis oocytes
Microtransplantation of mammalian brain neurolemma into the plasma membrane of Xenopus laevis oocytes has been used to study channels and receptors in their native form as they appear in the central nervous system. Use of microtransplanted neurolemma is advantageous for various reasons: tissue can be obtained from various sources and at different developmental stages; channels and receptors are present in their native configuration in their proper lipid environment along with appropriate auxiliary subunits; and it allows the evaluation of numerous channelopathies caused by neurotoxicants in an ex vivo state. Here, we show that Xenopus oocytes injected with post-natal day-90 rat brain neurolemma fragments successfully elicited ion currents upon membrane depolarization. Using a high-throughput two-electrode voltage clamp electrophysiological system, microtransplanted oocytes treated with niflumic acid generated inward, tetrodotoxin-sensitive currents upon pulsed depolarization (activation), which inactivated during prolonged depolarization in a manner similar to voltage-sensitive sodium channels (VSSC) heterologously expressed in oocytes following the injection of cRNA prepared from various VSSC isoforms when co-expressed with their beta subunits. Using this approach, the action of a well-established VSSC agonist, 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane (DDT), and a similarly acting type I pyrethroid, permethrin, were examined. The addition of DDT or permethrin resulted in a concentration-dependent increase in TTX-sensitive inward sodium current upon pulse-depolarization. Additionally, both DDT and permethrin resulted in a slowing of sodium channel inactivation kinetics. These results are consistent with the findings obtained using heterologous expression of single isoforms of rat brain VSSCs in Xenopus oocytes and with many other electrophysiological approaches, validating the use of the microtransplantation procedure as a toxicologically relevant ex vivo assay.
Murenzi, E., Snyder, M.C., Toltin, A.C., Symington, S.B. and Clark, J.M. 2017. Permethrin mimics the action of DDT on adult rat brain neurolemma microtransplanted into Xenopus laevis oocytes. Acta Hort. (ISHS) 1169:15-24
activation, inactivation, tetrodotoxin, voltage-sensitive sodium channels