Identification of Cell Types Corresponding to Microelectrode Impalements in Insect Midgut

Abstract

The chamber-mounted midgut of Manduca sexta larvae actively transports potassium ions from the hemolymph-side to the lumen-side. The midgut epithelium is composed of two major cell types, goblet and columnar cells. Microelectrode impalements previously performed on the midgut demonstrated two impalement types based on their distinct electrical potentials: the Low Potential Difference cell (LPD) and the High Potential Difference cell (HPD) (Blankemeyer and Harvey, 1978). The LPD and HPD impalement types have yet to be directly linked with the two histological cell types. The LPD impalement type has been shown to be the site of active transport due to resistance measurement changes seen in oxygen and anoxia, whereas the HPD impalement type has been shown to be not involved in active transport (Blankemeyer and Harvey., 1978). Using iontophoretic injection of fluorescent dye into LPD and HPD impalement types, we have located the dye-filled cells with the fluorescent microscope, and directly linked the goblet cell with the LPD impalement type and the columnar cell with the HPD impalement type. Thus, for the first time in this polymorphic tissue, the impalement type responsible for active ion transport, the LPD type, has been directly identified as the goblet cell.