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Nicotinic acetylcholine receptors are pentameric, typically being composed of two or more different subunits. To investigate which receptor subtypes are active in the heart, we initiated a series of experiments using an isolated perfused rat heart (Langendorff) preparation. Nicotine administration (100 M) caused a brief decrease (Ϫ7 Ϯ 2%) followed by a much larger increase (17 Ϯ 5%) in heart rate that slowly returned to baseline within 10 to 15 min. The nicotine-induced decrease in heart rate could be abolished by an ␣7-specific antagonist, ␣-bungarotoxin (100 nM). In contrast, the nicotine-induced increase in heart rate persisted in the presence of ␣-bungarotoxin. These results suggest that the nicotinic acetylcholine receptors (nAChRs) that mediate the initial decrease in heart rate probably contain ␣7 subunits, whereas those that mediate the increase in heart rate probably do not contain ␣7 subunits. To investigate which subunits may contribute to the nicotine-induced increase in heart rate, we repeated our experiments with cytisine, an agonist at nAChRs that contain ␤4 subunits. The cytisine results were similar to those obtained with nicotine, thereby suggesting that the nAChRs on sympathetic nerve terminals in the heart probably contain ␤4 subunits. Thus, the results of this study show that pharmacologically distinct nAChRs are responsible for the differential effects of nicotine on heart rate. More specifically, our results suggest that ␣7 subunits participate in the initial nicotine-induced heart rate decrease, whereas ␤4 subunits help to mediate the subsequent nicotine-induced rise in heart rate.

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We have constructed two mechanical snails, Robosnail 1 and Robosnail 2, inspired by the propulsion mechanisms of live gastropods. Each uses a different mechanical strategy to move on a thin layer of viscous fluid. Robosnail 1 uses a flexible flapping sheet to generate lubrication pressures in a viscous Newtonian fluid which in turn propels the snail. Robosnail 2 uses a compressible sliding sheet on a layer of Laponite, a non-Newtonian, finite-yield stress fluid.

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