The squid Alloteuthis subulata has a sophisticated statocyst-based balance system that enables it to detect its own orientation and movements. As a part of a programme to understand the operating principles of such systems, we are studying how the statocyst mechanosensory hair cells and primary afferent neurones interconnect and interact with each other. Intracellular recording from neighbouring primary or secondary mechanosensory hair cells have already shown that electrical coupling is widespread within the statocyst sensory epithelium. We have also demonstrated that the strength of the electrical coupling between the primary sensory hair cells is decreased in the presence of acetylcholine, and increased by application of dopamine. In contrast, these agents had no effect on the strength of electrical coupling between the secondary sensory hair cells.

Changes in cell coupling can be mediated through intracellular second messenger systems and adenosine 3Ì,5Ì-cyclic monophosphate (cAMP) has been reported to be involved in changes in cell coupling in other systems (e.g. Xin & Bloomfield, 1999). In the present work, using tissue isolated after humane killing of the animal, we tested whether the electrical coupling between the statocyst primary sensory hair cells is modulated by agents that change intracellular cAMP levels. We found that the adenylate cyclase activator, forskolin, significantly increased (P = 0.0002, Welch’s test) the strength of electrical coupling between sensory primary hair cells from a coupling coefficient of 0.2 ± 0.04 to 0.4 ± 0.05 (mean ± S.D., n = 5). We also studied the effect of the cAMP-elevating agent, 8-bromo-cAMP, on the strength of electrical coupling between primary hair cells. We found that this agent also significantly increased the coupling (P = 0.02, Welch’s test) between hair cells from 0.21 ± 0.07 to 0.44 ± 0.06 (n = 3). Similar results were also obtained with another cAMP-elevating agent, 3-isobutyl-1-methylxanthine (IBMX).

Since a variety of agents, acting through different mechanisms to modulate intracellular cAMP levels, all produce a similar change in cell coupling, we infer that cell coupling between squid primary sensory hair cells can be modulated by agents acting on intracellular cAMP levels. The next step is to investigate the effect of such cAMP-elevating agents on the known ionic conductances in these sensory hair cells (Chrachri & Williamson, 1997).This works was supported by the BBSRC and Wellcome Trust.

Chrachri, A. & Williamson, R. (1997). J. Neurophysiol. 78, 3125-3132.

Xin, D.Y. & Bloomfield, S.A. (1999). J. Comp. Neurol. 405, 75-87.