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141.
Posttetanic potentiation of human dorsiflexors 总被引:2,自引:0,他引:2
O'Leary, Deborah D., Karen Hope, and Digby G. Sale.Posttetanic potentiation of human dorsiflexors.J. Appl. Physiol. 83(6):2131-2138, 1997.Twitch contractions of the ankle dorsiflexors were evoked before and after applied 7-s tetanic stimulation at 100 Hzin 20 young adults. Torque decreased 15% during the tetanus. At 5 safter tetanus, twitch peak torque had potentiated 45%. Potentiationdeclined to 28% after 1 min, rose slightly to 33% at 2 min, anddeclined slowly with potentiation still 25% after 5 min. There waslarge intersubject variation in the amount of potentiation(5-140%) and its persistence (5 to 20 min). The muscle compoundaction potential (M wave) did not change significantly (from pretetanicvalue) at 5 s after tetanus but increased sharply (26%) at 2 min andthen subsided. Twitch half relaxation time (23%) decreasedsignificantly more than twitch rise time (13%) 5 s after tetanus andrecovered more slowly. Twitch rates of torque development (75%) andrelaxation (71%) increased similarly 5 s after tetanus and were stillelevated (~25%) at 5 min. The extent of twitch torque potentiationwas significantly inversely correlated with pretetanic twitch rise time(r = 0.69), half relaxation time (r = 0.61), andtwitch-to-tetanus ratio (r = 0.66). The data indicate that posttetanic potentiation has agreater effect on twitch half relaxation time than on time to peaktorque and is more prominent in muscles with a short twitch time courseand small twitch-to-tetanus ratio. 相似文献
142.
Dr. Mark E. McKinney Karen Rovang Dr. James C. Buell Dr. Robert S. Eliot 《Applied psychophysiology and biofeedback》1984,9(3):365-370
Impedance cardiography (ZCG), a noninvasive technique used to determine stroke volume and ventricular performance, is currently being utilized more extensively in psychophysiological research and may also prove a useful tool in the control of hypertension. To date, most studies employing ZCG have tested male subjects or patients. However, women and men differ on two important parameters used to calculate stroke volume: thoracic impedance (Zo), and the first derivative of change in impedance over time (dZ/dtmin). Examination of the clinical records of 19 females and 19 males, all nonmedicated, indicated that women had higher Zo levels (F(1, 36)=46.2,p<.0001) and higher dZ/dtmin levels (F(1, 36)=51.8, p<.0001), although calculated stroke volume indexes did not differ. A second sample of 10 women and 8 men, all healthy and nonmedicated, confirmed these findings. The differences in Zo are not due entirely to sex differences in height, weight, percent body fat, and subscapula skin-fold thickness, although these factors differ across sexes. It is important for researchers and clinicians utilizing ZCG with female subjects to be aware of these differences. 相似文献
143.
We have examined the shape and distribution of clathrin-coated pits in Swiss 3T3 cells at 4 or 37 degrees C using electron microscopy with serial sections and immunofluorescence light microscopy. Both groups were fixed in glutaraldehyde and preserved further using a membrane contrast enhancement technique consisting of sequential osmium-ferrocyanide, thiocarbohydrazide and osmium-ferrocyanide treatment in situ. Concanavalin A-horseradish peroxidase (conA-HRP) was used to identify these structures participating in endocytosis. Two hundred twenty-two clathrin-coated structures were analysed; 126 from cells fixed at 4 degrees C, and 96 from cells fixed after a 3 min warm-up to 37 degrees C. All coated structures labeled with conA-HRP had demonstrable connections to the plasma membrane. These coated structures were morphologically classified into three categories: (a) flat pits; (b) curved pits; and (c) pits with narrow-neck connections to the plasma membrane. At 37 degrees C, 27% of coated pits had narrow neck connections to the plasma membrane whereas at 4 degrees C only 1% had such connections. Receptosomes (endosomes) labeled with conA-HRP were found only after incubation at 37 degrees C, indicating that active endocytosis was occurring in cells at 37 degrees C, but not at 4 degrees C. Immunofluorescence with anti-clathrin antibody was used to quantitate the number of clathrin-coated pits in Swiss 3T3 cells incubated at 4 and 37 degrees C prior to fixation. No difference was detected. There were 426 +/- 122 pits per cell at 37 degrees C and 441 +/- 106 at 4 degrees C. These results support the hypothesis that formation of a narrow neck connected a coated pit to the cell surface is an early step in the mechanism of receptor-mediated endocytosis. 相似文献
144.
Localized Photosynthate Deposition in Citrus Fruit Segments Relative to Source-Leaf Position 总被引:1,自引:0,他引:1
Photosynthate translocation into fruit segments was examinedin Pineapple sweet orange Citrus sinensis (L.)Osbeck to determine whether previously reported patterns ofdistribution [Koch (1984) HortScience 19: 260] would changeover time or with alterations in balance between source leavesand sink fruit. In control plants, 14CO2 was supplied to a sourceleaf nearest the fruit for 1 h, followed by 5 h translocation.Over 89% of [14C]assimilates in the fruit were localized in4 segments directly aligned with the source and 73% of thesewere in the center 2 segments. Peel, pulp and seeds showed similarpatterns. Little or no lateral spreading of [14C]photosynthatesoccurred when an additional 7 days were allowed for translocation,but distribution was slightly broader when the source leaf was8 nodes farther from the fruit. Defoliation and girdling toreduce the source/sink ratio gave variable results if done 18h before experiments, but widened the area receiving [14C]assimilatesto approximately half the fruit if done 7 days earlier. Thisoccurred only when an entire fruit, was dependent upon a singlesource, leaving the opposite half fruit without an externalsupply of photosynthates. These data show an extreme degreeof preferential translocation and inflexibility which can occurin a transport path.
1Supported by United States Department of Agriculture CompetitiveResearch Grant 59-2121-1-1-752-0, Regional Project NC-142, andthe Institute of Food and Agricultural Sciences, Universityof Florida. (Received January 12, 1984; Accepted May 14, 1984) 相似文献
145.
Summary X-inactivation patterns were studied by replication analyses both in lymphocytes and skin fibroblasts of two patients carrying balanced X-autosome translocations, t(X;10)-(pter;q11) and t(X;17)(q11;q11), and one patient with an unbalanced translocation t(X;22)(p21;q11). Preferential late replication of the normal X chromosome was found in lymphocytes of both patients carrying balanced translocations and in skin fibroblasts of the patient carrying the translocation t(X;17). However, skin fibroblasts of the patient with a translocation t(X;10) showed preferential late replication of the abnormal der(X) chromosome with no spreading of late replication to the autosomal segment. In the case of unbalanced translocation t(X;22) there was preferential late replication of the der(X) chromosome both in lymphocytes and skin fibroblasts. The abnormal phenotype of the patients is discussed in relation to the observed X-inactivation patterns and the variability of the patterns in different tissues. 相似文献
146.
147.
Karen A. Sausman 《Zoo biology》1984,3(2):111-121
The survival rate of North American bighorn sheep, Ovis canadensis, housed in several zoological gardens was analyzed. Complete herd histories, including birth and death data as well as causes of mortality, were collected from seven institutions. Lambs were divided into inbred and noninbred animals, with lambs being considered inbred if they had an inbreeding coefficient greater than zero. The rate of survival of inbred and noninbred lambs was compared using “survival equalling one year” and “survival equalling six months.” Another analysis compared the survival rate of male and female inbred lambs and male and female noninbred lambs. Age at death was also compared in inbred and noninbred lambs. The analysis of the data for the seven collections, located in various geographic areas and housing various subspecies, indicates that inbreeding depression is a mortality factor in the captive management of North American bighorn sheep. Therefore, long-term survival of captive or isolated wild populations will depend on maintaining genetic diversity within the herds through careful selection of breeding stock in captive populations and introduction of nonrelated animals into isolated wild populations. 相似文献
148.
Summary In the spider Dinopis, retinae of the posterior median eyes synthesise new photoreceptor membrane in bulk at dusk and destroy it at dawn (Blest, 1978). During the dawn period, there is a rapid, anticipatory differentiation of unusual organelles from the rough endoplasmic reticulum (RER) in the intermediate segments of the receptors. This system is classified as GERL. Its products appear to play a role in the autolysis of photoreceptor membrane. Consistent topographical relationship to Golgi bodies has not been determined. Circumscribed regions of RER whorls first reorganise to yield fenestrated profiles; these differentiate further to a number of structures by condensation and loss of ribosomes. Smooth tubular profiles are termed rigid tubules to indicate their probable homology with the rigid lamellae of vertebrate secretory cells. More complex smooth multilocular bodies are also produced. Evidence is discussed which implies that both rigid tubules and multilocular bodies give rise to condensing vacuoles. These, in turn, pinch off coated vesicles assembled as Nebenkerne. Some rigid tubules are transported to the interrhabdomeral cytoplasm of the receptive segments. At late stages of differentiation, rigid tubules, multilocular bodies and Nebenkerne give strong, positive responses to zinc iodide-osmium tetroxide (ZIO) treatment; early stages and both cis and trans Golgi components do not. GERL differentiation is independent of immediate illumination of the retina at dawn. It is suggested to mediate the lysis of membrane degradation products by the production of hydrolases.We thank Professor D.T. Anderson F.R.S. for our use of field facilities at the Crommelin Biological Field Station of Sydney University at Warrah, Pearl Beach, N.S.W., and Andrew and Sally Austin and Sally Stowe for help in the field. We are indebted to Rod Whitty and the Electron Microscopy Unit for advice and support throughout these studies 相似文献
149.
Peter H. Byers Karen A. Holbrook Judith G. Hall Paul Bornstein John W. Chandler 《Human genetics》1978,40(2):157-169
Summary Several individuals from one family are described with a unique form of spondyloepiphyseal dysplasia. Characteristic features include shorttrunked short stature, punctate corneal dystrophy and marked disorganization of dermal collagen fibrils when examined by transmission electron microscopy. Inheritance is compatible with either dominance and a variable expression or X-linkage. Although the basic defect has not been determined, the tissue distribution is consistent with a defect in a non-collagenous component that affects collagen fibril formation or stability. 相似文献
150.