Voltage-gated ion channels regulate ion and fluid transport in Malpighian tubule epithelia of larval lepidopterans

Abstract

Insects account for ~80% of the world’s species, translating to approximately 200 million insects for every human. Moths and butterflies, from the order Lepidoptera, belong to second most diverse order of insects. The Cabbage Looper, Trichoplusia ni, is a prolific crop pollinator. Unfortunately, its larvae are worldwide agricultural pests because they consume copious quantities of food, eating 3-4 times their body weight in food daily, and growing 1000-fold in just a few weeks. These invasive agricultural crop pests are generalist feeders (eating >160 beneficial host plants) and consume large quantities of food to support their rapid growth. Rapid larval growth requires specialized regulatory mechanisms and an efficient excretory system. The Malpighian tubules (MTs) function as the insects’ primary excretory organ (equivalent to the vertebrate kidney), regulating ion and fluid transport, and xenobiotic and metabolic waste excretion. MT epithelium of larval lepidopterans is of particular interest because it can rapidly (~10 min) switch between ion reabsorption (where ions are transported from tubule lumen to hemolymph) and ion secretion (where ions are transported from hemolymph to tubule lumen). Recent studies have shown that this switch has been shown to be regulated in part by voltage-gated ion channels (VGICs). In larval T. ni, CaV1 channels expressed in the MTs distal ileac plexus region (DIP) have been shown to directly regulate K+ secretion. Pharmacological inhibition of voltage-gated ion channels (Kir1, HCN1, Cav1) independently from each other altered cell-based K+ transport. In the current study, biological assays measured changes in fluid secretion rate and membrane potential of MT epithelia of larval lepidopterans in response to pharmacological inhibition and/or activation of VGICs. In addition, immunohistochemistry assay using custom-made antibodies, revealed cellular and membrane localization of voltage-gated TRPA/ painless in the epithelia of the MT’s. In the current study we demonstrate that activating and inhibiting voltage-gated K+ and Ca2+ channels altered fluid secretion rate and membrane potential in the MTs of larval lepidopterans. VGICs have been extensively studied in excitable tissues. In contrast, their roles in the regulation of ion transport in the non-contractile, non-innervated epithelia of animals remains largely understudied. The novel data obtained in this study provides further insight about the fast-acting response mechanisms of VGICs, and how they play a vital role in the regulation of ion and water transp California State University startup and seed grant funding This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.