Sustaining olfaction at low salinities: Mapping ion flux associated with the olfactory sensilla of the blue crab Callinectes sapidus

To test the hypothesis of a diffusion-generated, ionic/osmotic microenviron ment within the olfactory sensilla (aesthetascs), flux: gradients of Ca2+ a nd K+ associated,vith the external surfaces of these sensilla were spatiall y mapped using self-referencing, ion-selective microelectrodes. Blue crabs (Callinectes sapidus) acclimated to low-salinity conditions (15 % sea water and fresh water) showed a net efflux of ions from the aesthetascs. The reg ion of maximum flux associated with each aesthetasc conformed to that predi cted from structural data and corresponded to the permeable region of the c uticle separating the olfactory dendrites from the external environment. Es timates of net flux from the entire tuft of aesthetascs for both Ca2+ and K + fell within the predicted range on the basis of comparisons with Na-22(+) flux measured previously and assuming a passive diffusion model of ion mov ement from the hemolymph to the sensillar lymph and, ultimately, to the ext ernal environment. The maximum concentrations of these ions measured deep w ithin the tuft are discussed in the light of a potential across the aesthet ascs that may limit ion efflux at low salinities.