Oxygen uptake and local Po2 profiles in submerged larvae of phaeoxantha klugii (Coleoptera: Cicindelidae), as well as their metabolic rate in air.

We studied whether oxygen uptake from the surrounding water might enhance survival in submerged third instar larvae of Phaeoxantha klugii, a tiger beetle from the central Amazonian floodplains. Local oxygen partial pressures (Po(2)) were measured with microcoaxial needle electrodes close to larvae submerged in initially air-saturated still water. The Po(2) profiles showed that the larvae exploit oxygen from the aquatic medium. Metabolism in the air of more or less resting larvae was determined by measuring the rate of CO(2) production (sV dot co2) with an infrared gas analyzer at 29 degrees C. The sV dot co2 was around 1.8 mu L g(-1) min(-1), equivalent to an oxygen consumption rate (sV dot o2) of 1.8-2.6 mu L g(-1) min(-1). Oxygen consumption (V dot o2) of individually submerged larvae measured in closed respiration chambers at 19-10.3 kPa Po(2) (initially air saturated, 29 degrees C) ranged between 0.05 and 0.2 mu L min(-1) and was not correlated with body mass. The sV dot o2 ranged between 0.1 and 0.4 mu L min(-1), that is, 4%-22% of the metabolic rate measured in air. Mean V dot o2 decreased with declining Po(2); however, some individuals showed contrary patterns. V dot o2 was additionally measured in dormant larvae, in larvae submerged for 1-2 d in open water or for 30-49 d within sediment, as well as in larvae exposed to anoxia before the measurements. The range of V dot o2 was similar in all groups, indicating that the larvae exploit oxygen from the water whenever available. Similar V dot o2 across the whole range of body mass investigated (0.31-0.76 g) suggests that oxygen uptake occurs by spiracular uptake. Assuming that larvae survive for some time at rates comparable to depressed metabolic rates reported for other insect species, it can be concluded that oxygen uptake from water can sustain aerobic metabolism even under quite severe hypoxia. It might therefore play an important role for survival during inundation periods.

Architecture and dynamics of microvillar photoreceptor membranes of a cephalopod.

Microvillar membranes of cephalopod photoreceptors, Eledone aldrovandii were analysed with respect to their protein and lipid composition. Molecular dynamics of this membrane type were investigated by ESR measurements using frog rod outer segment membranes as a reference system. The photoreceptor membrane is composed of about 56 wt% protein and 44 wt% lipid. Rhodopsin (mol wt 51 000) represents at least 70% of the membrane protein. The molar ratio of phospholipid to cholesterol to rhodopsin is about 55:24:1. Phosphatidylcholine (28.9 mol%) and phosphatidylethanolamine (27.8 mol%) are the major phospholipids. The ESR measurements suggest that the cephalopod photoreceptor membrane is less fluid than from rod outer segment membranes although the major phospholipids show remarkable high levels of polyunsaturated fatty acids (e.g. 88 mol% in phosphatidylethanolamine). It is concluded that the lower fluidity of microvillar membranes results in part from high cholesterol content and that a restricted mobility of rhodopsin in this membrane does not result only from the fact that the membrane is rolled into a microvillar structure.