Expression of extracellular calcium-sensing receptor by human lens epithelial cells

The extracellular calcium-sensing receptor (CaR) confers the capacity to sense small changes in the extracellular Ca²⁺ concentration (Ca₀²⁺) not only upon cells involved in maintaining systemic Ca²⁺ homeostasis but also upon those not directly involved in this process. Since high Ca₀²⁺ is known to affect various physiological processes in lens epithelium both in health and in disease states (e.g., the formation of cataracts in hypocalcemic states), we investigated the expression and function of the CaR in these cells. By RT-PCR and immunocytochemistry the CaR is expressed in human lens epithelial cells in culture. In addition, the open state probability of a Ca²⁺-activated potassium (K⁺) channel with a conductance of 82 +/- 3 pS is significantly increased by elevating Ca₀²⁺ to 3.0 mM or by application of 100 μM neomycin, both effective CaR agonists. Therefore, our data suggest that human lens epithelial cells express the CaR, which may be functionally linked to Ca²⁺-activated K⁺ channels and, perhaps, to other ion channels involved in ionic homeostasis in the lens.