Fig. 3. Summary of acid-regulating systems present in bovine lens cells in the presence (A) and absence of bicarbonate (B). The original sources for the membrane potential and ironic data are given.68 Note the greater buffering capacity where HCO3- is present and that the quadruple ion exchanger can still operate in the absence of HCO3-. The lactate (L-) cotransporter is the only system that appears to be independent of other ionic gradients.