Effects of electrically induced fatigue on the twitch and tetanus of paralyzed soleus muscle in humans

Shields, Richard K., Laura Frey Law, Brenda Reiling, KellySass, and Jason Wilwert. Effects of electrically induced fatigueon the twitch and tetanus of paralyzed soleus muscle in humans.J. Appl. Physiol. 82(5):1499-1507, 1997.We analyzed the twitch and summated torque(tetanus) during repetitive activation and recovery of the human soleusmuscle in individuals with spinal cord injury. Thirteen individualswith complete paralysis (9 chronic, 4 acute) had the tibial nerveactivated every 1,500 ms with a 20-Hz train (7 stimuli) for 300 ms anda single pulse at 1,100 ms. The stimulation protocol lasted 3 min andincluded 120 twitches and 120 tetani. Minimal changes were found forthe acute group. The chronic group showed a significant reduction inthe torque and a significant slowing of the contractile speeds of boththe twitch and tetanus. The decrease in the peak twitch torque was significantly greater than the decrease in the peak tetanus torque early during the fatigue protocol for the chronic group. The twitch time to peak and half relaxation time were prolonged during fatigue, which was associated with improved fusion of the tetanus torque. At theend of the fatigue protocol, the decrease in the peak twitch torque wasnot significantly different from the decrease in the peak tetanustorque. After 5 min of rest, the contractile speeds recovered causingthe tetanus to become unfused, but the tetanus torque became lessdepressed than the twitch torque. The differential responses for thetwitch and the tetanus suggest an interplay between optimal fusioncreated from contractile speed slowing and excitation contractioncoupling compromise. These issues make the optimal design of functionalelectrical stimulation systems a formidable task.

     

Notes on the genus Pteroceras (Orchidaceae)

A new name (Pteroceras semiteretifolium H. Æ. Peders.) and two new combinations (P. cladostachyum (Hook.f.) H. Æ. Peders., P. unguiculatum (Lindley) H. Æ. Peders.) are presented. The correct application of the name P. pallidum (Blume) Holttum is discussed.     

Evolution of structure and function of V-ATPases

Proton pumping ATPases/ATPsynthases are found in all groups of present-day organisms. The structure of V- and F-type ATPases/ATP synthases is very conserved throughout evolution. Sequence analysis shows that the V- and F-type ATPases evolved from the same enzyme already present in the last common ancestor of all known extant life forms. The catalytic and noncatalytic subunits found in the dissociable head groups of the V/F-type ATPases are paralogous subunits, i.e., these two types of subunits evolved from a common ancestral gene. The gene duplication giving rise to these two genes (i.e., encoding the catalytic and noncatalytic subunits) predates the time of the last common ancestor.Mapping of gene duplication events that occurred in the evolution of the proteolipid, the noncatalytic and the catalytic subunits, onto the tree of life leads to a prediction for the likely subunit structure of the encoded ATPases. A correlation between structure and function of V/F-ATPases has been established for present-day organisms. Implications resulting from this correlation for the bioenergetics operative in proto-eukaryotes and in the last common ancestor are presented. The similarities of the V/F-ATPase subunits to an ATPase-like protein that was implicated to play a role in flagellar assembly are evaluated.Different V-ATPase isoforms have been detected in some higher eukaryotes. These data are analyzed with respect to the possible function of the different isoforms (tissue specific, organelle specific) and with respect to the point in their evolution when these gene duplications giving rise to the isoforms had occurred, i.e., how far these isoforms are distributed.     

Inheritance of the group I rDNA intron in Tetrahymena pigmentosa

We have previously argued from phylogenetic sequence data that the group I intron in the rRNA genes of Tetrahymena was acquired by different Tetrahymena species at different times during evolution. We have now approached the question of intron mobility experimentally by crossing intron⁺ and intron^? strains looking for a strong polarity in the inheritance of the intron (intron homing). Based on the genetic analysis we find that the intron in T. pigmentosa is inherited as a neutral character and that intron⁺ and intron^? alleles segregate in a Mendelian fashion with no sign of intron homing. In an analysis of vegetatively growing cells containing intron⁺ and intron^? rDNA, initially in the same macronucleus, we similarly find no evidence of intron homing. During the course of this work, we observed to our surprise that progeny clones from some crosses contained three types of rDNA. One possible explanation is that T. pigmentosa has two rdn loci in contrast to the single locus found in T. thermophila. Some of the progeny clones from the genetic analysis were expanded for several hundred generations, and allelic assortment of the rDNA was demonstrated by subcloning analysis. © 1992 Wiley-Liss, Inc.     

A quantitative and qualitative study of blood monocytes in patients with bronchogenic carcinoma

Summary Absolute circulating number and functions of blood monocytes (i.e., pinocytosis, phagocytosis, and chemotaxis) were studied in 25 patients with untreated bronchogenic carcinoma and in 28 control subjects. The absolute circulating monocyte count was increased in 20 (80%) of the patients. There was no difference in the pinocytic and phagocytic activity of patient and control monocytes. In contrast, patient monocytes showed depressed chemotactic responsiveness. This defect was more severe in small cell anaplastic carcinoma than in the other histologic types of bronchogenic carcinoma (P=0.001), and may explain the difference in macrophage infiltration seen in solid tumours of the lung. There was no correlation between chemotaxis and clinical stage. Depressed chemotaxis may be related to a plasma factor, since patient plasma inhibited the chemotaxis of control monocytes as well as the activity of chemotactic agents. The defective chemotaxis and the presence of plasma inhibitory activity may interfere with the ability of blood monocytes to accumulate as macrophages in tumour sites. Abbreviations used in this paper are: MCR, monocyte chemotactic response; SAC, small cell anaplastic bronchogenic carcinoma; OBC, non-small cell bronchogenic carcinoma MEM, Eagle's minimal essential medium; CFI, chemotactic factor inhibitor(s); HSA, human serum albumin