DETECTION OF WEAK ELECTRIC-FIELDS BY SHARKS, RAYS, AND SKATES

The elasmobranchs-sharks, rays, and skates-can detect very weak electr ic fields in their aqueous environment through a complex sensory syste m, the ampullae of Lorenzini. The ampullae are conducting tubes that c onnect the surface of the animal to its interior. In the presence of a n electric field, the potential of the surface of the animal will diff er from that of the interior and that potential is applied across the apical membrane of the special sensory cells that line the ampullae. T he firing rate of the afferent neurons that transmit signals from the ampullae has been shown to vary with that potential. We show that thos e firing rates can be described quantitatively in terms of synchronous firing of the sensory cells that feed the neurons. We demonstrate tha t such synchronism follows naturally from a hypothetical weak cell-to- cell interaction that results in a self-organization of the sensory ce lls. Moreover, the pulse rates of those cells-and the neurons that ser vice the cells-can be expected to vary with the imposed electric field s in accord with measured values through actions of voltage gated tran smembrane proteins in the apical sector of the cell membranes that adm it Ca++ ions. We also present a more conjectural model of signal proce ssing at the neuron level that could exploit small differences in firi ng rates of nerve fibers servicing different ampullae to send an unamb iguous signal to the central nervous system of the animal. (C) 1998 Am erican Institute of Physics.