Voltage-gated calcium channels regulate K+ transport in the Malpighian tubules of the larval cabbage looper, Trichoplusia ni

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 alpha 1, beta 2, and alpha 2 delta 4 subunits of voltage-gated Ca2+ channel Ca(V)1 and that pan-Ca-v alpha immunoreactivity is present in the apical and basolateral membranes of the principal cells. Basolateral membrane potential (V-bl) in isolated MTs of larval Trichoplusia ni was influenced by Ca(V)1 functioning; pharmacological inhibition of Ca(V)1 reversed V-bl from inside-negative to inside-positive, and also reduced transepithelial potential (V-te), lowered [Ca2+](i) and reversed the direction of K+ transport from secretion to reabsorption. Thus, our findings indicate that a functional Ca(V)1 channel is necessary for constitutive K+ secretion observed in isolated preparations of lepidopteran MTs. Lastly, V-te and V-bl of isolated MTs were influenced by changes in bathing saline [K+]. Our findings suggest that epithelia may rely on Ca-V channels to enable robust ion secretion and downregulation of Ca-V channels, together with other transcriptional changes, enables ion reabsorption.

Automated summary

Transporting epithelia are specialized tissues in directional movements of ions and water. Recent studies on lepidopteran Malpighian tubule have shown the importance of voltage-gated Ca2+ channels in ion secretion and reabsorption. Findings suggest that Ca(V)1 channels play a crucial role in K+ secretion in lepidopteran MTs, and changes in bathing saline [K+] can also influence ion transport.