Caffeine and ryanodine differentially modify a calcium-dependent component of soma action potentials in identified molluscan (Lymnaea stagnalis) neurones In situ

1. The main objectives of the present study were to investigate the effects of either caffeine or ryanodine on action potential shape in four identified neurones of Lymnaea stagnalis (L) in situ.

2. The action potential width at half-amplitude (half-width, HW) is a Ca²⁺ -dependent phenomenon and hence it was used here as a measure of spike broadening or narrowing. Spike data were analysed using a computer programme and appropriate statistical tests were performed.

3. Intracellular recordings were made under control conditions to establish the frequency/HW relationship for each cell type. Recordings were also made from each cell after perfusion with two concentrations of each drug and their effects on the frequency/HW relationship were studied.

4. Caffeine produced a significant increase in HW in three out of four studied neurones, whilst ryanodine produced a significant response in only one neurone and inconsistent results in the remainder. Therefore, both drugs were found to produce cell specific responses.

5. The data presented here are consistent with previous studies which demonstrate that both caffeine and ryanodine act as mobilizing agents for intracellular calcium from internal storage sites, although by different mechanisms.