Berlin 2005 – scientific programme

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AKB: Biologische Physik

AKB 75: Nonlinear Phenomena and Pattern Formation

AKB 75.1: Invited Talk

Wednesday, March 9, 2005, 10:15–10:45, TU H2013

The Physics of Chemoreception - an Encore — •U. Benjamin Kaupp — Forschungszentrum Jülich, Institut für Biologische Informationsverarbeitung 1, 52425 Jülich

Sperm can navigate in a chemical gradient of attractants released by the egg. The attractant molecules bind to specific receptors on the surface of the sperm flagellum. Activation of receptors initiates a cellular signaling pathway. Within milliseconds, the intracellular messenger cyclic GMP is synthesized. This messenger opens ion channels in the envelope membrane, and Ca ions are flowing into the cell. A sperm cell is exquisitely sensitive: it can respond to the binding of a single attractant molecule. At the same time, sperm respond over a broad range of attractant concentrations (ca. 5 orders of magnitude). This remarkable dynamic range is achieved by two mechanisms. First, the receptor rapidly inactivates; second, the receptor lowers its binding affinity at higher states of occupancy. Both mechanisms enable sperm to escape saturation at high attractant concentrations near the egg. The increase in [Ca] changes the beat pattern of the flagellum. In the unstimulated state, sperm swim in circles. Upon activation by the attractant, sperm undergo a sequence of turns and straight swimming (’turn-and-run’). In a chemical gradient, the behavioural pattern produces epicycloid movements towards the source. The sequence of alternating ’turns’ and ’runs’ is produced by Ca oscillations in the flagellum that are evoked by the attractant. The Ca oscillations change the properties of motor proteins by unknown mechanisms.