Figure 7

Na⁺ transport by the rectum of A. taeniorhynchus larvae. (A) A representative scan of Na⁺ flux at locations along the rectum of larval A. taeniorhynchus. The length and direction of the arrows represent the magnitude and direction of net Na⁺ transepithelial flux respectively (IN = intestine; MT = Malpighian tubule; Na⁺ ME = Na⁺ selective microelectrode). Scale bar units are in pmol cm⁻² s⁻¹ (vertical = flux) and mm (horizontal). (B) The rate of Na⁺ transport at the posterior rectum and the anterior rectum of A. taeniorhynchus larvae reared in freshwater (FW) or seawater (SW). A positive rate of transport indicates efflux (from lumen to bath) and a negative rate of transport represents influx (from bath to lumen). Values are expressed as mean ± SEM with n = 6 for FW and n = 12 for SW. A comparison of Na⁺ transport rates in FW and SW larvae was performed with unpaired t-test for both posterior (p = 0.02) and anterior rectum (p < 0.001).