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Biomedical subjects

S K Malhotra

Publications and source records attributed to S K Malhotra.

12 recordsLinked to original sources
PubMed1979

alpha-bungarotoxin binding sites (acetylcholine receptors) in denervated mammalian sarcolemma.

The nonsynaptic sarcolemma of denervated skeletal muscle of rat shows an abundance of approximately 15 nm intramembranous particles on the P face. These particles are either singly distributed or are in clusters, and they are essentialy lacking from the comparable freeze-fractures of the innervated sarcolemma. Autoradiographic studies using 125I-alpha-bungarotoxin (BGT) on 1 mu-thick sections, and freeze-etch studies using ferritin-alpha-BGT conjugates on membrane fractions, show that the distribution of the label corresponds to the distribution of the 15-nm particles in the nonsynaptic sarcolemma. On the basis of these results and existing physiologic and biochemical data, it is suggested that the 15-nm intramembranous particles are components of the alpha-BGT binding sites, ie, acetylcholine (Ach) receptors, in the nonsynaptic sarcolemma of denervated muscle and that the two types of distributions represent two spatial manifestations of Ach receptor molecules. The significance of these findings in relation to synapse formation in denervated muscle is discussed.

Acetylcholine↗
PubMed1979

Visualization of mitochondrial coupling factor F1(ATPase) by freeze-drying.

It is known that the negatively stained preparations of inner mitochondrial membrane display characteristic approximately 9 nm F1 (ATPase) knobs projecting from the matrix surface. Freeze-etch studies have reported the absence of such knobs from the "etched" surface of the inner mitochondrial membranes. We have demonstrated their presence on the surface of SMP (submitochondrial particles) prepared by freeze-drying for transmission electron microscopy. This identification has been substantiated by comparison with freeze-dried TU particles (trypsin-urea treated SMP) that are devoid of F1 (ATPase). It has been suggested that a layer of water molecules is strongly adsorbed to the surface of SMP and does not sublime during normal freeze-"etching."

Adenosine Triphosphatases↗
PubMed1978

Plasma membrane of Phycomyces: sequential changes in the structure during spore formation.

The plasma membrane of sporangiospores (spores) of Phycomyces blakeleeanus has distinct structural features that distinguish it from the plasma membrane of the sporangiophores. The plasma membrane of the spores is, however, derived from that of the sporangiophore. A study of sequential development of spores shows that the mass of cytoplasm in a sporangial initial is cleavaged by proliferation and subsequent anastomosis and membrane fusion of the clevage vesicles. The plasma membrane of the cleavage vesicles has a reversed curvature (inside out) to that of the sporangial plasma membrane. Otherwise, the distribution of intercalated membranous particles (Imp) on the fractured faces is similar to that of the plasma membrane of the sporangium. Lather, as a result of fusion of cleavage vesicles, curvature of the plasma membrane in the spore initials returns to their original state. In the processes of spore maturation, a new type of structural feature appears in the plasma membrane, which is not present either in the plasma membrane of spore initials or in the plasma membrane of sporangiophores or mycelia. This feature often is seen as large particles (30--35 nm) which are randomly distributed on the exoplasmic face (EF) with corresponding depressions on the plasmic half (PF) in freeze-fractured replicas. They increase in number with increasing spore maturity. These particles are, in fact, the inward protrusions of the plasma membrane of the spore. A change in the number of 5--8 nm intramembranous particles on the fractured faces is also noted during spor maturation, with an increase on the EF face and a corresponding decrease on the PF face. This alteration may result from vertical movement of Imp or from a change in the fracture plane as a consequence of alteration in the lipid content during maturation.

Cell Membrane↗
PubMed1977

The mandibular foramen: its anteroposterior position.

This study has been conducted on forty-five Asiatic skulls and sixty-two mixed skulls of black and white Americans to determine the anteroposterior relationship of the mandibular foramen. The mean size of the anterior dimension was greater than the mean size of the posterior dimension of the ramus in all instances. The mandibular foramen was found to be located in the third quadrant anteroposteriorly. The lingula was located just anterior to the mandibular foramen. There was no right- or left-side dominance in the ramus size and position of the mandibular foramen. No appreciable difference was noted in the location of mandibular foramen in the two groups studied.

Asia↗
PubMed1977

The significance of cAMP induced alterations in the cellular structure of Phycomyces.

Effect of cyclic AMP (cAMP) on Phycomyces blakesleeanus was studied by growing sporangiospores on glucose-asparagine agar or liquid medium containing three different levels of cAMP (10, 20 and 40 micronM) in addition to the control (no cAMP added). The response of Phycomyces to the exogenous cAMP concentration in the medium is as follows: (1) the time required for germ tube emergence is reduced; (2) the diameter of the mycelium is increased (sometimes more than 10 times) and frequency of branching is also increased; (3) the cell wall of the mycelium is thickened (in some cases more than 5 times); (4) the glycogen in the cytoplasm is decreased as visualized in thin sections and also demonstrated in biochemical quantitation; and (5) the distribution of intercalated membranous particles (Imp) on plasma membrane is altered and this can be easily detected in freeze-fractured replica. Such a change in Imp is seen in the formation of small clusters of aggregated particles on the plasmic half (PF) and craters on the complementary exoplasmic half (EF) of the plasma membrane. Although the mechanism of cAMP action requires further exploration, it is possible that the addition of cAMP to the culture medium leads to degradation of glycogen and enhancement of chitin synthesis since the cell wall is largely composed of chitin. The alteration in Imp may be related to a change in the activity of chitin synthetase which is a plasma membrane-bound enzyme.

Cyclic AMP↗
PubMed1977

Nerve-muscle interaction: changes in the cellular organization of a skeletal muscle upon denervation.

The alterations in the organization of lumbrical muscle of the rat have been investigated following denervation, with emphasis on the structure of cytoplasmic constituents, sarcolemma in the synaptic and non-synaptic regions and acetylcholinesterase activity. The appearance of 15--18 nm intramenbranous particles in the non-synaptic sarcolemma is thought to be related to the known acetylcholine extrajunctional sensitivity which is manifested after denervation. The acetylcholinesterase activity is greatly reduced in the synaptic region in the denervated muscle. These changes are discussed in relation to the known physiological and biochemical data.

Acetylcholinesterase↗
PubMed1976

Is the nexus necessary for cell-to-cell coupling of smooth muscle?

Electronmicroscopic study of electrically coupled smooth muscles was undertaken to determine the distribution of nexuses in various types of smooth muscle. The study revealed that while nexal structures were commonplace in some types of smooth muscle, they were very rare or absent in others, even though in some cases these cells were only a few nanometers distant from one another. The persistence in thin section of these structures in the main circular muscle of dog intestine after poor fixation, fixation under strain, cell shrinkage, and metabolic damage of various sorts seems to rule out the thesis that they are labile. The absence of nexuses in longitudinal muscle of dog intestine examined both by thin section and by freeze fracture suggests that in this tissue they are absent or very rare in vivo and cannot account for electrical coupling. Nexuses were discernible in thin sections of main circular muscle after a variety of experimental conditions of fixation. Metabolic inhibition or in vitro permanganate fixation partially destroyed nexal contacts. These procedures induced tissue, membrane apposition and an accompanying increase in the number of structures which resemble nexuses at low magnification (nexus-like structures). "Nexus-like" structures occurred in all smooth muscle fixed by in vitro permanganate associated with apposition of membranes and poor preservation of basement membrane. A technique of in vitro permanganate fixation was developed which prevented tissue swelling; consequently "nexus-like" structures were absent in tissues so treated. The suggestion is made that some structures described in the literature as nexuses, following permanganate fixation, may represent "nexus-like" structures. The balance of evidence suggests that nexuses need not be present for electrical coupling of some smooth muscle cells, in which other types of cell-to-cell contacts must be invoked.

Animals↗
PubMed1976

The formation of sporangiospores in Phycomyces.

The multinucleate state of the vegetative spores of Phycomyces blakesleeanus arises as a consequence of cleavage of cytoplasm containing a variable number (1-6) of pre-existing nuclei. No nuclear division or incorporation of 3H-thymidine was detected during maturation of the spores.

Cell Nucleus↗