It is widely known that the composition of the aqueous humor of different species varies, particularly with regard to the Cl
− and HCO
3 − concentrations.
43 44 45 46 In humans, for example, Cl
− concentration is higher and HCO
3 − concentration is lower in the posterior chamber than their concentrations in the plasma, whereas in the rabbit the reverse is true.
43 44 45 46 Most transport studies of the isolated rabbit ciliary epithelium have yielded results consistent with the in vivo higher-than-plasma concentration of HCO
3 − in the aqueous.
8 39 47 48 Even in the recent paper by Crook et al.,
42 bumetanide inhibited only 43% of the I
sc, the remainder of which may be a net HCO
3 − flux. Evidence indicative of a net HCO
3 − flux across the rabbit ciliary epithelium was provided by Wolosin et al.,
14 15 and Butler et al.,
16 who demonstrated an asymmetry in the expression of HCO
3 − transporters in the nonpigmented and pigmented epithelia. The latter exhibited the alkali-loading Na
+-dependent Cl
−/HCO
3 − exchanger, whereas the dominant bicarbonate transporters of the former resulted in HCO
3 − efflux. In the isolated bovine ciliary body, in contrast, previous findings show a net Cl
− transport toward the aqueous,
10 40 49 which is consistent with a higher-than-plasma concentration of Cl
− in the aqueous humor, as found in humans.