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The Journal of Neuroscience, August 15, 1999, 19(16):6838-6843

Unmasking of a Novel Potassium Current in Drosophila by a Mutation and Drugs

Amandeep Singh^{1, 2} and Satpal Singh¹

¹ Department of Biochemical Pharmacology, State University of New York at Buffalo, Buffalo, New York 14260, and ²  Williamsville North High School, Williamsville, New York 14221

The delayed rectifier potassium current plays a critical role in cellular physiology. This current (I_K) in Drosophila larvae is believed to be a single current. However, a likely null mutation in the Shab K⁺ channel gene (Shab³) reduces I_K but does not eliminate it. This raises a question as to whether or not the entire I_K passes through channels encoded by one gene. Similarly, an incomplete blockade of I_K by high concentrations of quinidine, a selective I_K blocker, raises a question as to whether I_K consists of two components that are differentially sensitive to quinidine. We have addressed these questions by a combined use of genetics, pharmacology, and physiology. The current component removed by the Shab³ mutation differed from the remaining component in activation kinetics, inactivation kinetics, threshold of activation, and voltage dependence. The two components showed strong differences in sensitivity to quinidine. Physiological properties of the current component removed by the Shab³ mutation were similar to those of the quinidine-sensitive fraction of I_K. Complementary to this, properties of the current component remaining in the Shab³ mutant muscles were similar to those of the quinidine-resistant fraction of I_K. These observations strongly suggest that, in contrast to the current belief, I_K consists of two components in Drosophila, which are genetically, pharmacologically, and physiologically distinct. These components are being called I_KS and I_KF. I_KS is carried via Shab-encoded channels. I_KF defines a new voltage-activated K⁺ current in Drosophila.

Key words: Drosophila; K⁺ channels; Shab; delayed rectifier; larval muscles; quinidine

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Copyright © 1999 Society for Neuroscience  0270-6474/99/19166838-06$05.00/0

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