Ion channels can be modulated by closely associated binding proteins.Among the ion channels subject to such modulation is the large conductance calcium-and voltage-activated potassium channel encoded by the Slowpoke gene in the fruit fly Drosophila.In a heterologous expression system, the Slowpoke channel binding partner Slob shifts the voltage-dependence of channel activation in the depolarizing direction, thereby effectively inhibiting the channel.To determine whether Slowpoke modulation by Slob influences neuronal physiology, we carried out in vivo patch recordings from neurons in the pars intercerebralis (PI) region of the fly brain.In flies in which Slob expression is disrupted, by either P-element mutagenesis or targeted expression of Slob-RNAi, the voltage dependence of Slowpoke activation in PI neurons is shifted in the hyperpolarizing direction, consistent with the results from heterologous expression.Furthermore, the duration of action potentials in the PI neurons is shorter in Slob knockout flies, reflecting the fact that Slowpoke contributes to action potential repolarization.The PI neurons express and release Drosophila insulin-like peptides (DILPS) that regulate metabolism, feeding and lifespan.Slob knockout flies survive starvation conditions longer than their wild type counterparts, indicating that Slob modulation of Slowpoke channels influences DILP secretion.Furthermore, Slob knockout increases insulin pathway signaling, and thereby decreases circulating sugar levels, again consistent with an effect of Slob on DILP release.The results demonstrate that ion channel modulation by an intimately-associated channel binding protein can produce profound alterations in neuronal physiology and behavior.