Predicted profiles of ion concentrations in olfactory cilia in the steady state

The role of ciliary geometry for transduction events was explored by numeri cal simulation. The changes in intraciliary ion concentrations, suspected t o occur during transduction, could thus be estimated. The case of a single excised cilium, having a uniform distribution of membrane channels, voltage clamped to -80 mV, was especially investigated, The axial profile of membr ane voltage was that of a leaky cable, The Ca2+ concentration profile tende d to show a maximum in proximal segments, due to a preponderance of Ca2+ in flow over Ca2+ export at those locations. The local increase in Ca2+ concen tration activated Cl- channels. The resulting current caused a local drop i n Cl- concentration, especially at the tip of the cilium and in distal segm ents, accompanied by a drop in ciliary K+ concentration. In consequence, th e membrane Cl- current was low in distal segments but stronger in proximal segments, where resupply was sufficient. The model predicts that the Cl- de pletion will codetermine the time course of the receptor potential or curre nt and the ciliary stimulus-response curve. In conclusion, when modeling wi th transduction elements presently known to participate, the ciliary geomet ry has large effects on ion distributions and transduction currents because ciliary ion transport is limited by axial electrodiffusion.