Demonstration of Voltage-Dependent and TTX-Sensitive Na+-Channels in Human Melanocytes

The electrophysiological properties of cultured human melanocytes were investigated using the whole-cell configuration of the patch-clamp technique. Depolarizations to membrane potentials more positive than -30 mV resulted in the rapid development (<1 ms to peak) of an inward current. The maximum peak current was observed at +10 mV and reached an average amplitude of about 270 pA. During the depolarizations, the current inactivated with a time constant of about 2 ms. The current was abolished by the addition of 0.3 μM tetrodotoxin, a blocker of voltage-gated Na⁺-channels, and disappeared when Na⁺ was omitted from the extracellular medium. In addition, the melanocytes contain at least two types of outward K⁺-current. The first type, observed in every cell, was highly sensitive (K_i 1 mM) to the K⁺-channel blocker TEA, required depolarizations beyond zero to be activated and did not inactivate. The second type was less regularly observed (10% of the cells). This current activated at more negative voltages (–20 mV), was resistant to TEA (20 mM) but was blocked by 2 mM 4-aminopyridine and inactivated rapidly during depolarizations. We conclude that human melanocytes are equipped with voltage-dependent Na⁺-channels, a delayed rectifying K⁺-current and a K⁺-current similar to the A-current in neurones.     

Action Spectra for in vivo and in vitro Conversions of Phycochrome b, a Reversibly Photochromic Pigment in a Blue-Green Alga, and Its Separation from Other Pigments

Phycochrome b, one of the reversibly photochromic pigments found in Tolypothrix distorta seems to exist in only two forms: P^b₅₀₀ and P^b₅₇₀. The pigment has been spectroscopically demonstrated in vivo. It has also been separated from other pigments. Two different methods for separation have been used: isoelectric focusing and gel filtration. Preparations of purified phycobilisomes contain phycochrome b. The in vivo and in vitro absorption difference spectra were determined as well as action spectra for the conversions in vitro and in vivo of P^b₅₀₀ to P^b₅₇₀ and vice versa. Transformation kinetics of phycochrome b show that the conversions in both directions are initially first-order reactions.     

Inhibition of photosynthetic electron transport and formation of inactive chlorophyll in winter stressed Pinus silvestris

Kinetics of fluorescence at room temperature, electron transport and photooxidation of P700 and cytochrome f have been studied in chloroplasts isolated from active and winter stressed Pinus silvestris. The winter stress induced block in the electron transport chain between the two photosystems is close to the site of plastoquinone, since winter stress and DCMU caused the same type of inhibition of the reoxidation of the primary electron acceptor Q of photosystem II. No winter inhibition of the electron transport between cytochrome f and P700 was observed. Time course studies of P700 photooxidation in chloroplasts of active and winter stressed pine have shown that the photosynthetic unit size must be about equal in the two types of chloroplasts. An apparent increase of the photosynthetic unit size was induced by winter stress, as revealed by the high chlorophyll/P700 ratio of winter stressed pine. The phenomenon is explained by the formation of photosynthetically inactive chlorophyll. Low-temperature fluorescence emission spectra were recorded when either chlorophyll a (433 nm) or chlorophyll b (477 nm) were preferentially excited. Winter stress induced the formation of a chlorophyll a fraction emitting at 673 nm. This chlorophyll is most likely derived from the chlorophyll a antennae of the two photosystems, and it probably contributes to the photosynthetically inactive pool of chlorophyll in winter stressed pine. The light harvesting chlorophyll a/b complex is relatively resistant to winter stress.     

Invertebrate colonization of a new, man-made stream in southern Sweden

SUMMARY.

• 1 The invertebrate colonization of a man-made stream, Flugströmmen, in southern Sweden was monitored for 18 months in 1988 and 1989. Benthic samples were taken on twelve occasions from three sites (upstream, middle and downstream) and community structure was compared with that at ten natural, permanent reference sites nearby.
• 2 The number of species colonizing increased rapidly during the first 3 months. The increase was most rapid upstream but levelled off during the second year at this site, while numbers continued to increase downstream.
• 3 Simuliid species were the earliest colonizers and reached high densities at upstream and middle sites during the first year. Ephemeropteran and plecopteran species also occurred early on, whereas Coleoptera, Odonata and Trichoptera were, on average, slower to colonize. Blackfly densities decreased upstream after the first year and hydropsychids became numerically dominant.
• 4 The colonization order of functional feeding groups was as predicted: filter feeders first, grazers/collectors intermediate, predators and shredders last.
• 5 After a year, the community structure in Flugströmmen closely resembled that in lake-outlet streams situated in the area, although communities at the three sites within the stream were most similar to one another.
• 6 The possible role of competitive and predatory processes in determining the observed successional patterns are discussed.

     

Phycochromes b and d: their occurrence in some phycoerythrocyanin-containing blue-green algae (cyanobacteria)

Abstract
Phycochromes b and d, two types of photoreversibly photochromic pigments previously extracted from the blue-green alga Tolypothrix distorta , which contains phycoerythrocyanin, have now been found in three Anabaena strains also containing phycoerythrocyanin. Tests for the presence of phycochromes b and d in a number of blue-green algae lacking phycoerythrocyanin have been negative. The possibility that phycochrome b-type absorbance changes are due to changes in the α-subunit of phycoerythrocyanin is discussed.     

The Devonian nekton revolution

Klug, C., Kröger, B., Kiessling, W., Mullins, G.L., Servais, T., Frýda, J., Korn, D. & Turner, S. 2009: The Devonian nekton revolution. Lethaia, 10.1111/j.1502‐3931.2009.00206.x Traditional analyses of Early Phanerozoic marine diversity at the genus level show an explosive radiation of marine life until the Late Ordovician, followed by a phase of erratic decline continuing until the end of the Palaeozoic, whereas a more recent analysis extends the duration of this early radiation into the Devonian. This catch‐all approach hides an evolutionary and ecological key event long after the Ordovician radiation: the rapid occupation of the free water column by animals during the Devonian. Here, we explore the timing of the occupation of the water column in the Palaeozoic and test the hypothesis that ecological escalation led to fundamental evolutionary changes in the mid‐Palaeozoic marine water column. According to our analyses, demersal and nektonic modes of life were probably initially driven by competition in the diversity‐saturated benthic habitats together with the availability of abundant planktonic food. Escalatory feedback then promoted the rapid rise of nekton in the Devonian as suggested by the sequence and tempo of water‐column occupation. □Devonian, diversity, ecology, food webs, nekton, plankton, radiation.     

Some aspects of life strategies of Early Palaeozoic rugose corals

Examination of some well-preserved specimens of Silurian rugose corals from Gotland reveals that the following categories of life strategies can be distinguished: ambitopic, liberosessile, fixosessile, rhizosessile and possibly limited vagile. Most solitary rugose corals appear to have been liberosessile and are characterized by initial attachment to a small sediment grain but subsequently becoming recumbent on a soft substrate. Detailed studies of Phaulactis angelini, Holophragma calceoloides, Laccophyllum lindstroemi, Rhegmaphyllum conulus and Rhabdocyclus ocksaroensis n. sp., and comparison with earlier described species, provide some new aspects on different life strategies for solitary corals.     

Decarboxylation and Transport of Auxin in Segments of Sunflower and Cabbage Roots. II. A Chromatographic Study Using IAA-1-14C and IAA-5-3H

The polar movement of IAA has been examined in 5-mm root segments of Brassica oleracea and Helianthus annum. The movement was studied partly with IAA-1-¹⁴C and partly with IAA-5-³H. In both plants a slight acropetal flux of ¹⁴C and IAA-³H was found through the segments. The recovered radioactivity in the agar receiver blocks and in the receiver end of the segments increased as a function of time. A large portion of the applied IAA was converted on the cut surfaces and in the tissues of the segments. Chromatographic analysis indicated different destruction products when estimated by scintillation counting and by spraying with in-dole reagent (DMCA). Chromatograms run in isopropanol: ammonia: water, 8:1:1, yielded three different substances, one spot near the starting line and one near the front, neither of which has been identified. Finally there was a spot with R_f 0.4–0.6, probably representing IAA.