Coding efficiency and information rates in transmembrane signaling

A variety of cell types responds to hormonal stimuli by repetitive spikes i n the intracellular concentration of calcium ([Ca2 + ](i)) which have been demonstrated to encode information in their frequency, amplitude, and durat ion. These [Ca2 + ](i)-spike trains ale able to specifically regulate disti nct cellular functions. Using a mathematical model for receptor-controlled [Ca-2 (+) ](i) oscillations in hepatocytes we investigate the encoding of f luctuating hormonal signals in [Ca2 + ](i)-spike trains. The transmembrane information transfer is quantified by using an information-theoretic revers e-engineering approach which allows to reconstruct the dynamic hormonal sti mulus from the [Ca2 + ](i)-spike trains. This approach allows to estimate t he accuracy of coding as well as the rate of transmembrane information tran sfer. We found that up to 87% of the dynamic stimulus information can be en coded in the [Ca-2 (+) ](i)-spike train at a maximum information transfer r ate of 1.1 bit per [Ca2 + ](i)-spike. These numerical results for humoral i nformation transfer are in the same order as in a number of sensory neurona l systems despite several orders of magnitude different time scales of oper ation suggesting a universal principle of information processing in both bi ological systems. (C) 2000 Elsevier Science Ireland Ltd. All rights reserve d.