K⁺ transport in Malpighian tubules of Tenebrio molitor L.: is a K_ATP channel involved? Available to Purchase

The presence of ATP-regulated K⁺ (K_ATP) channels in Tenebrio molitor Malpighian tubules was investigated by examining the effect of glibenclamide on both fluid secretion and basolateral membrane potentials (V_bl). Glibenclamide, a K_ATP channel blocker, slowed fluid secretion of Tenebrio tubules. In low bath K⁺ concentration (5 mmol l^-1), glibenclamide either hyperpolarized or depolarized V_bl, resembling the effect seen with Ba²⁺. Subsequent addition of 6 mmol l^-1Ba²⁺ caused a further hyper- or depolarization of V_bl. In control Ringer (50 mmol l^-1 KCl, 90 mmol l^-1 NaCl), glibenclamide had no visible effect on V_bl. The effect of ouabain was investigated in low bath[K⁺] in the presence of Ba²⁺. V_blresponded by a small but significant hyperpolarization from -51±4 mV to-56±4 mV (n=16, P<0.001) in response to 1 mmol l^-1 ouabain. Repeating the experiments in the presence of both glibenclamide and Ba²⁺ resulted in a depolarization of V_bl when ouabain was added. In low bath [K⁺](high Na⁺), the Na⁺/K⁺-ATPase is expected to function at a high rate. In the presence of Ba²⁺, replacing Na⁺ by K⁺ rapidly depolarized V_bl,but this was followed by a repolarization. Repeating the experiments in the presence of glibenclamide markedly reduced the depolarizing effect and abolished the repolarization, with a gradual decrease in the sensitivity of V_bl to the surrounding [K⁺]. These results suggest the presence of K_ATP channels in the basolateral membrane. Glibenclamide had no visible effect on V_bl in high K⁺ or in the absence of Ba²⁺, indicating that other highly conductive K⁺ channels may mask the effect on K_ATP channels. This is the first demonstration of the presence of K_ATP channels in an insect epithelium.