Transfected Cyclic Nucleotide–Gated Channels as Biosensors

The cyclic nucleotides, cyclic AMP and cyclic GMP, like intracellular calcium, are involved in a vast array of intracellular signaling processes. But knowledge of the cellular and subcellular concentrations of cAMP and cGMP, and of the kinetics and spatial distributions of the changes of their concentration in situ, have lagged far behind our knowledge of the corresponding features of calcium signaling, which were propelled by developments in calcium-sensing dyes and imaging technology (Tsien, 1989, 1998). In this issue, J.W. Karpen and colleagues advance the issue of cAMP measurement in living cells by developing and convincingly calibrating the use of transfected cyclic nucleotide–gated channels as cAMP sensors (Rich et al., 2000).