Raised intracellular free calcium within the lens causes opacification and cellular uncoupling in the frog.

Ion‐sensitive micro‐electrodes were used to measure the levels of intracellular free Ca2+ within the intact amphibian lens. The free [Ca2+] was found to constitute 0.4% of the total lens calcium. The pCa measured at the anterior lens surface was found to 6.59, while that at the posterior was 5.70. An 8‐fold anterior/posterior Ca2+ gradient thus exists along the optical axis. The intracellular free Ca2+ could be manipulated by incubating the lens in high‐Ca2+ or cA2+‐free EGTA Ringer solutions. Raising the intracellular free Ca2+ to 0.22 mM caused lens opacification and cellular uncoupling; the coupling ratio was reduced from 1 in control to 0.41 in high Ca2+.