Several visual degenerative diseases (Best disease, autosomal dominant vitreoretinochoroidopathy, and autosomal recessive bestrophinopathy) result in macular visual loss in adulthood and are associated with mutations in the VMD2 gene. The protein product of the VMD2 gene, bestrophin-1, is expressed in the basolateral membrane of the retinal pigment epithelium and has been shown to form functional Cl^– channels when expressed heterologously (Hartzell et al, 2008). Here, we describe experiments that examined the interactions of bestrophin-1 with cations. HEK293 cells were transfected with cDNA for wild-type human VMD2. Cl^– channel activity was measured using whole cell patch clamp and a bath solution containing a high NaCl or NMDG-Cl concentration. The pipette contained 38.4 mM Cl^– and the principle intracellular cation was either Cs⁺ or NMDG⁺. Intracellular Ca²⁺ was buffered to 500nM. Cells transfected with WT bestrophin-1 exhibited large outwardly rectifying Cl^– currents in response to step potentials (Vm = -120 to +80 mV) from a holding Vm of -50 mV. G_out was 20.7±4.5 nS and V_rev of -19.0±2.0 in Na⁺ bath solution. However, when NMDG⁺ was used to replace all Na⁺ and Cs⁺ in the bath and pipette solutions respectively, the outward conductance was reduced to 9.5±2.7nS (n=13 and 15 respectively, P<0.05). Untransfected cells showed no significant Cl- current. These data suggest that the Cl- conductance of bestrophin may be modulated by the cationic environment. In a further series of experiments, performed with the Na⁺ bath solution, we observed an increase in inward current when step potentials were evoked from a holding Vm of +80mV rather than -50mV. Thus, the inward conductance was 11.6±3.1nS from -50mV and 26.9±9.6nS from +80mV (n=10). The magnitude of this inward current developed over time so that the maximum current was observed 78±9s after changing holding Vm. The increased inward current was also associated with a positive shift in V_rev (+19.1±4.2mV). One explanation for this observation is that Na⁺ may be permeating the bestrophin channel. This conclusion is further supported by the finding that there was no significant increase in inward current when recording from cells bathed in NMDG⁺-containing solutions. These data suggest that cations influence the Cl^– conductance of bestrophin-1 and may, under certain conditions, permeate this channel.