Voltage-gated calcium channels regulate K+ transport in the Malpighian tubules of the larval cabbage looper, Trichoplusia ni
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Transporting epithelia are tissues that specialize in the directional movements of ions and water and are typically either secretory or reabsorptive. Recent work on the Malpighian tubule of larval lepidopterans (caterpillars) demonstrated that the distal ileac plexus segment of this epithelium is capable of rapidly switching between ion secretion and reabsorption. Subsequent transcriptomic studies suggested expression of voltage-gated ion channels in the lepidopteran MTs (which are not contractile and not innervated). The present study shows that isolated MTs of larval Trichoplusia ni express α1, β2, and α2δ4 subunits of voltage-gated Ca2+ channel CaV1 and that pan-CaVα immunoreactivity is present in the apical and basolateral membranes of the principal cells. Basolateral membrane potential (Vbl) in isolated MTs of larval Trichoplusia ni was influenced by CaV1 functioning; pharmacological inhibition of CaV1 reversed Vbl from inside-negative to inside-positive, and also reduced transepithelial potential (Vte), lowered [Ca2+]i and reversed the direction of K+ transport from secretion to reabsorption. Thus, our findings indicate that a functional CaV1 channel is necessary for constitutive K+ secretion observed in isolated preparations of lepidopteran MTs. Lastly, Vte and Vbl of isolated MTs were influenced by changes in bathing saline [K+]. Our findings suggest that epithelia may rely on CaV channels to enable robust ion secretion and downregulation of CaV channels, together with other transcriptional changes, enables ion reabsorption.
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