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Terrestrial snails which live under dry and hot conditions need efficient mechanisms of adaptation to counteract the problems of desiccation and over-heating. A profoundly heat tolerant snail species is the Mediterranean Xeropicta derbentina, exhibiting different shell colour morphs ranging from pale white to darkly banded. Considering that dark-pigmented snails are believed to have a disadvantage due to faster heating, we investigated possible differences in the stress markers Hsp70 and lipid peroxideation between four pre-defined colour morphs which were exposed to different temperatures for eight hours. The highest Hsp70 levels were observed in response to 38-40°C. Levels decreased when this temperature was exceeded. Snails of a pre-defined colour category 3 (with a large black band at the umbilicus side of the shell) showed the most prominent Hsp70 response. Lipid peroxideation levels also showed a maximum at 38°C but displayed a second peak at rather high temperatures at which the Hsp70 level already had decreased (45-48°C). Particularly pure white snails (category 1) and the most pigmented ones (category 4) were found to have different levels of lipid peroxidation at 38°C and 45°C compared to the other morphs. A hypothesis involving a combined two-phase defence mechanism, to which both, the Hsp70 protection system and the antioxidant defence system, may contribute, is discussed.

*EM and TC contributed equally to this work. BACKGROUND AND PURPOSE 5-HT increases force and L-type Ca2+ current (I Ca,L ) and causes arrhythmias through 5-HT 4 receptors in human atrium. In permanent atrial fibrillation (peAF), atrial force responses to 5-HT are blunted, arrhythmias abolished but I Ca,L responses only moderately attenuated. We investigated whether, in peAF, this could be due to an increased function of PDE3 and/or PDE4, using the inhibitors cilostamide (300 nM) and rolipram (1 μM) respectively. EXPERIMENTAL APPROACHContractile force, arrhythmic contractions and I Ca,L were assessed in right atrial trabeculae and myocytes, obtained from patients with sinus rhythm (SR), paroxysmal atrial fibrillation (pAF) and peAF. KEY RESULTSMaximum force responses to 5-HT were reduced to 15% in peAF, but not in pAF. Cilostamide, but not rolipram, increased both the blunted force responses to 5-HT in peAF and the inotropic potency of 5-HT fourfold to sevenfold in trabeculae of patients with SR, pAF and peAF. Lusitropic responses to 5-HT were not decreased in peAF. Responses of I Ca,L to 5-HT did not differ and were unaffected by cilostamide or rolipram in myocytes from patients with SR or peAF. Concurrent cilostamide and rolipram increased 5-HT's propensity to elicit arrhythmias in trabeculae from patients with SR, but not with peAF. CONCLUSIONS AND IMPLICATIONSPDE3, but not PDE4, reduced inotropic responses to 5-HT in peAF, independently of lusitropy and I Ca,L , but PDE3 activity was the same as that in patients with SR and pAF. Atrial remodelling in peAF abolished the facilitation of 5-HT to induce arrhythmias by inhibition of PDE3 plus PDE4. Abbreviations

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