关键词: 棉铃虫, 抗药性, 三氟氯氰菊酯, 霍乱毒素, L-型钙通道, 膜片钳技术, 神经细胞

Abstract:

Cholera toxin (CTX) activates the α_subunit of stimulatory heterotrimeric G-proteins (G_αs) and stimulates voltage-gated L-type (Ca²⁺_(L)) channels, which may be primary targets of pyrethroids. To investigate the potential mechanisms underlying the resistance to pyrethroids in agriculturally important insect pests, we examined the modulations by CTX of Ca²⁺_(L) channels in the central neurons of the cyhalothrin-resistant (Cy-R) and cyhalothrin-susceptible (Cy-S) cotton bollworms (Helicoverpa armigera). Neurons were isolated from the 3rd-4th instar larvae of the Cy-R and Cy-S cotton bollworms, respectively. The isolated neurons from each group were cultured for 12-16 h in an improved L15 insect culture medium with or without CTX (700 ng/mL). Barium currents (I_Ba) through Ca²⁺_(L) channels were recorded by the whole-cell patch-clamp technique. The results showed that CTX increased the I_Ba peak current density by 36.1 % and caused a hyperpolarizing shift by 5 mV in the I-V curve in the Cy-S neurons, but had no such effect in the Cy-R neurons. Moreover, CTX exerted little effects on other parameters such as the activation potential, reverse potential, activation and inactivation curves in either Cy-S or Cy-R neurons. No significant differences of the parameters mentioned above in the Ca²⁺_(L) channels were detected between the Cy-S and Cy-R neurons cultured without CTX. The results suggest that the Gs-adenylyl cyclase (AC)-cAMP-protein kinase A (PKA)-Ca²⁺_(L) channel signal transduction pathway may exist in cotton bollworm neurons, and the reduced sensitivity of Ca²⁺_(L)channels to the CTX modulation in the Cy-R neurons (but not in the Cy-S neurons) may account for the reduced nerve sensitivity in the pyrethroids-resistant insects.

Key words: Helicoverpa armigera, resistance, cyhalothrin, cholera toxin, L-type voltage-gated calcium channels, patch-clamp technique, neurons