Increase of sodium current after pyrethroid insecticides in mouse neuroblastoma cells

Abstract

The effects of 4 different pyrethroid insecticides on sodium channel gating in internally perfused, cultured mouse neuroblastoma cells were studied using the suction pipette, voltage clamp technique. Pyrethroids increased the amplitude of the sodium current, sometimes by more than 200%. Activation of the sodium current occurred at more hyperpolarized potentials than under control conditions. The declining phase of the sodium current during depolarization was markedly slowed down and after repolarization of the membrane a large, slowly decaying sodium tail current developed. Pyrethroids did not affect the sodium current reversal potential, steady-state sodium inactivation or recovery from sodium channel inactivation. The amplitude of the pyrethroid-induced slow tail current was always proportional to the sodium current at the end of the preceding depolarizing pulse. The rate of decay of the slow tail current strongly depended on pyrethroid structure and increased in the order deitamethrin, cyphenothrin, fenfluthrin and phenothrin. The rate of decay further depended on membrane potential and temperature. Below -85 mV the instantaneous current-voltage relationship of the slow tail current showed a negative slope conductance. The tail current decayed more slowly at low temperatures. Arrhenius plots indicated that the relaxation of open sodium channels to a closed state in,,olved a higher energy barrier for pyrethroid-affected than for normal channels. The energy barrier was higher after deitamethrin than after the non-cyano pyrethroid fenfluthrin. It is concluded that in mammalian neuronal membrane pyrethroids selectively reduce the rate of closing of sodium channels both during depolarizatio~ and after repelarization of the nerve membrane.

Influence of Lipid-Soluble Gating Modifier Toxins on Sodium Influx in Neocortical Neurons

“…These toxins include hydrophilic toxins such as tetrodotoxin, saxitoxin, and -conotoxin (receptor site 1); lipid-soluble alkaloid toxins, including batrachotoxin, veratridine, acotinine, and grayanotoxin (receptor site 2); polypeptide toxins, such as ␣-scorpion toxins, sea anemone toxins, and some spider toxins (receptor site 3); ␤-scorpion toxins (receptor site 4); brevetoxins (PbTxs) and ciguatoxins originating from the marine dinoflagellates Karenia brevis and Gambierdiscus toxicus, respectively (receptor site 5); and ␦-conotoxins (receptor site 6). In addition, pyrethroid insecticides act at a site distinct from these better characterized neurotoxin receptor sites on the sodium channel ␣-subunit to enhance channel activity by shifting activation to more negative membrane potentials as well as by inhibiting inactivation (Ruigt et al, 1987). More recently, a structurally unique lipopeptide toxin, antillatoxin, produced by the marine cyanobacterium, Lyngbya majuscula, has been demonstrated to be a potent VGSC activator at yet another distinct receptor site (Berman et al, 1999;Li et al, 2001).…”

Kinetics of the membrane current mediated by serotonin 5‐HT3 receptors in cultured mouse neuroblastoma cells.

“…Ionic currents were measured under voltage clamp combined with perfusion of single cells according to methods previously developed (Lee, Akaike & Brown, 1980;Ruigt, Neijt, van der Zalm & van den Bercken, 1987). Fire-polished suction pipettes (tip diameter, [8][9][10][11][12] ,um; resistance, 400-600 kQ) were used to obtain tight seals between the pipette and the cell.…”

Synergistic Actions of Pyridostigmine Bromide and Insecticides on Muscle and Vascular Nociceptors

“…However, mammalian Na v proteins are structurally diverse and anatomically specialized to a much greater extent than those expressed in invertebrates. Although the functional significance is obscure, the influence of pyrethroids on distinct mammalian Na v differ qualitatively and quantitatively (Ruigt, et al 1987;Song et al, 1996a,b;Meacham, et al., 2008; Soderlund 2009, Soderlund, 2010). Much significance has been attached to thermal modulation of Na v vulnerability.…”

“…However, mammalian Na v proteins are structurally diverse and anatomically specialized to a much greater extent than those expressed in invertebrates. Although the functional significance is obscure, the influence of pyrethroids on distinct mammalian Na v differ qualitatively and quantitatively (Ruigt, et al 1987; Song et al, 1996a,b;Meacham, et al, , 1972;van den Bercken et al, 1977;Cutkomp and Subramanyam, 1986; Salgado et al, 1989). This temperature dependence would seem to preclude pyrethroid actions on mammals whose body temperature hovers near 37° C. Nevertheless, it is well documented that exposure to permethrin formulations causes pain and paresthesia in humans lasting minutes to hours (Kolmodin-Hedman et al, 1982;Tucker and Flannigan, 1983;Flannigan and Tucker, 1985;Gotoh, et al, 1998; see Wolansky and Harrill, 2008).…”