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The S-layer of the fish pathogen Aeromonas salmonicida, the causative agent of furunculosis in salmonids, is probably the best characterized S-layer in regards to function. Not only does it constitute an important determinant in pathogenesis (Ishiguro et al., 1981), but it has also been assigned specific virulence functions (reviewed by Kay and Trust, 1991). We have recently demonstrated that the S-layer of A. salmonicida (or A-layer) possesses significant flexibility and plasticity. It normally exists in a single type of lattice capable of adopting different conformations (Garduno and Kay, 1992a), but under calcium depletion it forms two novel structural patterns as a consequence of structural rearrangements within the layer (Garduno et al., 1992). It is the objective of this present work to explore the functional relevance of one of these novel structural patterns, the “big squares” pattern.

Our interest in calcium currents arose from our intention to approach an understanding of excitation-contraction coupling in muscle fibers from Balanus (Bacigalupo et al., 1979; Hidalgo et al., 1979; Luxoro and Nassar-Gentina, 1984). For a full account of recent developments on the subject, the student is referred to recent reviews (Reuter, 1979; Hagiwara and Byerly, 1981; Tsien, 1983; Kostyuk, 1984).