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1.
Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium 总被引:13,自引:9,他引:4
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Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel. 相似文献
2.
Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal 总被引:10,自引:9,他引:1
We have developed a new approach to the measurement of phylogenetic signal
in character state matrices called relative apparent synapomorphy analysis
(RASA). RASA provides a deterministic, statistical measure of natural
cladistic hierarchy (phylogenetic signal) in character state matrices. The
method works by determining whether a measure of the rate of increase of
cladistic similarity among pairs of taxa as a function of phenetic
similarity is greater than a null equiprobable rate of increase. Our
investigation of the utility and limitations of RASA using simulated and
bacteriophage T7 data sets indicates that the method has numerous
advantages over existing measures of signal. A first advantage is
computational efficiency. A second advantage is that RASA employs known
methods of statistical inference, providing measurable sensitivity and
power. The performance of RASA is examined under various conditions of
branching evolution as the number of characters, character states per
character, and mutations per branch length are varied. RASA appears to
provide an unbiased and reliable measure of phylogenetic signal, and the
general approach promises to be useful in the development of new techniques
that should increase the rigor and reliability of phylogenetic estimates.
相似文献
3.
Differences in diet and behaviour of sympatric saithe and pollack in a Scottish sea loch 总被引:1,自引:0,他引:1
Two closely related and morphologically similar gadoid predators, saithe, Pollachius virens and pollack P. pollachius , coexist in close proximity on a submerged reef in Loch Ewe, Scotland. The degree of overlap between the niches of these two gadoids in the wild was investigated by means of acoustic tracking, underwater television and an examination of stomach contents. Simultaneous tracking of individuals of both species revealed that pollack generally swim more slowly than saithe, restricting much of their movements to the submerged reef. Saithe ranged more widely around the reef as part of a school during the day, moving onto the reef at night. Video recordings showed that saithe swam actively and foraged in small groups and took prey items from the kelp, whereas pollack tended to remain solitary, maintained station at particular locations for minutes at a time and apparently used the kelp forest exclusively for cover. Although the dietary overlap of the two predators was considerable, their intake of different prey groups varied. In particular, within the crustaceans, saithe took amphipods, while pollack took mysids. In addition, saithe consume a wider range of prey than pollack. The relationship between the movement patterns and the use of food resources by these two predators is discussed, with particular emphasis on differences in feeding strategies. 相似文献
4.
5.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献
6.
Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
7.
8.
P Agostinis J Van Lint S Sarno P De Witte J R Vandenheede W Merlevede 《The Journal of biological chemistry》1992,267(14):9732-9737
Treatment of quiescent Swiss 3T3 mouse fibroblasts with bombesin resulted in a rapid 6-8-fold stimulation of cytosolic Ser/Thr kinase activities toward the S6 peptide (RRLSSLR), myelin basic protein (MBP), and the G peptide (SPQPSRRGSESSEE). Anion exchange Mono Q chromatography resolved multiple S6 peptide- and G peptide kinase activities and two MBP kinase peaks. Both MBP- and several S6 peptide kinase peaks could be inactivated by PCSL (PP2A2) phosphatase action. This indicates that the bombesin-induced activation of these enzymes is mediated by a Ser/Thr phosphorylation event. The S6 peptide kinases as well as the two MBP kinases stimulated in response to bombesin are similar to those activated by epidermal growth factor in Swiss 3T3 fibroblasts which suggests that the early events of the signal transduction pathway mediated by these growth factors in Swiss 3T3 cells may converge in the activation of common Ser/Thr kinases. Bombesin, which acts as a sole mitogen for Swiss 3T3 fibroblasts, also produced a several-fold increase in the kinase activity toward the RRREEESEEE peptide, a specific substrate for CK-2. This kinase activity was heparin-sensitive and also measurable with the G peptide (SPQPSRRGSESSEE) and GS-1 peptide (YRRAAVPPSPSPSLSRHSSPHQSEDEE), which contain consensus sequences for phosphorylation by CK-2. The bombesin-stimulated CK-2 activity could not be measured in whole cytosols but was revealed by the anion exchange chromatography step. The activation of CK-2 was not reversed by PCSL phosphatase action. The implication of CK-2 in the signal transduction pathway of bombesin is discussed. 相似文献
9.
To lek or not to lek: mating strategies of male fallow deer 总被引:5,自引:1,他引:4
Apollonio Marco; Festa-Bianchet Marco; Mari Franco; Mattioli Stefano; Sarno Benedetta 《Behavioral ecology》1992,3(1):25-31
We studied the mating system of fallow deer (Dama dama) for6 years in central Italy. Males in this population could defendterritories that were either single, clumped in leks, or satelliteto leks. The most highly successful males in our study werein leks. When we considered all males, there were no significantdifferences in average copulatory success according to territorytype because many lek males did not achieve any copulations,which were seen in only a few lek territories. The variancein copulatory success, however, was much greater for leks thanelsewhere. Single territories were occupied for shorter timesduring the rut than lek territories. Fighting among males wasmore frequent in the lek, even when we excluded highly successfullek males from the analysis. Chases of nonterritorial malesand harem size were correlated with the number of copulationsachieved by individual males, but did not vary according toterritory type. Copulatory success of some individuals increasedwith age, but there were no age differences among males holdingdifferent types of territories. Satellite males switched tolek territoriality in the course of one rut, but switches fromsingle territory to lek territory were rare. We suggest thatmales in single territories are inferior competitors that selecta low-risk, lowbenefit strategy, whereas those in lek territorieswhere no copulations were seen may be attempting to establishthemselves on the lek to increase their copulatory success infuture years. 相似文献
10.