Aim: 

Cnidarians have mechanisms of defence and predation performed by stinging cells, nematocytes, provided with a secretory product, the nematocyst. The nematocyst includes the capsule fluid containing various toxins and an inverted tubule. Following a proper stimulus the tubule is rapidly everted, thereby injecting the toxins. Volume regulation under hyposmotic shock, essential to cell survival, has been recently observed in isolated nematocytes. Such response, termed regulatory volume decrease (RVD), is attained through a complex mechanism involving channels and ion transporters. The present contribute aims to study the role of K⁺ and Cl^- independent conductive pathways and that of K-Cl cotransport (KCC) in RVD of isolated nematocytes.

Methods: 

Nematocytes were isolated by 605 mM SCN^- treatment from acontia of Aiptasia mutabilis (Anthozoa) living in the Strait of Messina (Italy). RVD test was performed by applying 35% hyposmotic shock. Either quinine, or barium, or NO₃^- substitution, or furosemide, or DIDS, or NPPB were alternatively employed to verify the role of both K⁺ and Cl^- efflux.

Results: 

Barium, DIDS and furosemide have been found to partially reduce RVD, whereas total inhibition of RVD after treatment with either quinine or NPPB or NO3^- substitution was observed. Inhibition due to the latter treatment may interestingly account for a relevant role of KCC.

Conclusion: 

From our results arises the coexistence of both K⁺ and Cl^- conductive pathways and KCC in nematocytes, as described in other cells. Further studies are needed to better ascertain the presence of KCC in so primitive eukaryotic cells.