Short Communication: Luminal Alkalinization by the Isolated Midgut of the Tobacco Hornworm (Manduca Sexta)

ABSTRACT The midgut contents of lepidopteran larvae are often several pH units more basic than the haemolymph (Berenbaum, 1980). One species, Manduca sexta, maintains a luminal pH of 11.3 (Dow, 1984) while the haemolymph has a pH of 6.7-6.8 (Dow, 1984; Dow et al. 1984). The midgut of M. sexta is divided into three morphologically distinct regions (Cioffi, 1979), and Dow (1984) has shown that the luminal pH is greatest in the anterior and middle sections of the midgut. The posterior midgut lumen, while still more basic than the haemolymph, has a pH lower than the middle and anterior sections. Whereas these results suggest that alkaline secretion may differ along the length of the midgut, no direct measurements of alkaline secretion have been made. In this study the rate of luminal alkalinization in the three midgut sections was measured in vitro.