Ca²⁺-dependent arrest of cilia without uncoupling epithelial cells

IN CERTAIN ciliated epithelia, for example, mussel gill lateral cell epithelium, metachronally coordinated ciliary beat can be arrested systematically, either after nervous¹ or local stimulation, for example by laser microinjury^2,3. In the latter case, the velocity of spread of arrest, its extent and decremental character suggest that the response depends on electrotonic coupling of the gill cells³. The lateral cells are coupled by extensive septate junctions and small gap junctions ⁴, more basally located, which may act in a manner homologous to electrical synapses of nerve and muscle cells^5-7. Although intracellular microelectrode recordings of lateral cell depolarisation accompanying arrest after branchial nerve stimulation have been made in Mytilus¹, there are no reports of microelectrode studies of cell coupling in gill cells. We have used experimentally-induced spreading arrest to monitor the state of coupling in the lateral cell epithelium of a freshwater mussel (for example, Elliptio complanatus).