Adaptation in chemoreceptor cells

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Abstract
The cross-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using NH4 receptor cells, of known spectral tuning, from the lobster (Homarus americanus). Spectrum experiments: The spectral tuning of NH4 receptor cells was investigated using NH4Cl and 7 other compounds selected as the most stimulatory non-best compounds for NH4 cells from a longer list of compounds tested in previous studies. Based on their responses to the compounds tested, 3 spectral subpopulations of NH4 cells were revealed: NH4-Glu cells which responded second-best to Glutamate (Glu); NH4- Bet cells which responded second-best to Betaine (Bet); and ‘pure’ NH4 cells, which responded to NH4C1 only (Fig. 1). Cross-adaptation experiments: Overall, cross-adaptation with Glu and Bet backgrounds caused suppression of response of NH4 receptor cells to various concentrations of NH4Cl. However, the different subpopulations of NH4 cells were affected differently: (a) The stimulus-response functions of NH4-Glu cells were significantly suppressed by both a 3 μM (G3) and 300 μM (G300) Glu backgrounds, (b) The stimulus-response functions of NH4-Bet cells was not affected by a 3 μM (B3), but significantly suppressed by a 300μM (B300) Bet background. (c) The stimulus-response functions of pure NH4 cells were not affected by any of the Glu or Bet backgrounds (Figs. 3, 4). The stimulus-response functions of 5 cells from all different subpopulations were enhanced by cross-adaptation with the G300 and B300 backgrounds (Fig. 4, Table 1). Whereas self-adaptation caused parallel shifts in stimulus-response functions (Borroni and Atema 1988), cross-adaptation caused a decrease in slope of stimulus-response functions. Implications of the results from cross- and self-adaptation experiments on NH4 receptor cells, for a receptor cell model are discussed.