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J Calvo

Publications and source records attributed to J Calvo.

At least 73 records · Page 4Linked to original sources
PubMed1987

Modulation of calcium channels of twitch skeletal muscle fibres of the frog by adrenaline and cyclic adenosine monophosphate.

1. Modulation of fast and slow Ca2+ channels of frog skeletal muscle by adrenaline (10(-6) to 10(-5) M) and cyclic AMP was investigated using intracellular voltage recordings in intact fibres and a voltage-clamp technique in cut fibres. 2. In tetraethylammonium (TEA), Cl(-)-free Ringer solution, adrenaline increased the maximum rate of rise of Ca2+ spikes by 85% and in a similar solution, peak slow Ca2+ current (ICa,s) by 51%. 3. Application of cyclic AMP to the cut ends of fibres, produced a relative increase of ICa,s of ca. 24%. The effect was maintained for ca. 2 h. 4. Changes in the time course of ICa,s were produced by adrenaline and cyclic AMP: the limiting values of time-to-peak current measured as a function of membrane potential were lower (ca. 41% in adrenaline and ca. 34% in cyclic AMP) than those found in control experiments. Also, ICa,s decayed faster in the presence of adrenaline or cyclic AMP. These changes can be explained by exhaustion of Ca2+ in the lumen of transverse tubular system and do not require the assumption of kinetic variations. 5. Fast Ca2+ currents (ICa,f) which could not be blocked by nifedipine were also recorded. Cyclic AMP greatly increased the amplitude of ICa,f but had no obvious effects on ICa,f kinetics. 6. Application of catalytic subunit of cyclic AMP-dependent protein kinase by diffusion or by pressure injection also increased the amplitude of ICa,s and ICa,f. Pressure injection brought about modifications in the time course of ICa,s that cannot be explained by depletion of Ca2+. 7. Mechanical experiments were performed on single fibres. Nominally Ca2+-free solutions prevented the development and the maintenance of positive inotropic effect of adrenaline on twitch tension. Development of twitch potentiation was dependent upon the frequency of stimulation. Adrenaline was practically ineffective if no stimulation was applied. 8. It is concluded that both populations of Ca2+ channels are modulated by adrenergic stimulation probably via cyclic AMP, and that twitch potentiation may be mediated by a Ca2+ entry through Ca2+ channels.

Action Potentials↗
PubMed1987

Ultrastructural study on the origin of rat microglia cells.

An ultrastructural study of the origin of microglial cells has been performed in albino rat brains taken from 17-day-old embryos up to 35-day-old rats. Invasion of the nervous parenchyma by macrophagic cells which appear in mesodermal sources is described. Although the two main microglial sources are the meningeal membranes and the vascular adventitia, pericytes may also participate in the formation of microglial cells.

Animals↗
PubMed1987

Appearance of microglial cells in the postnatal rat retina.

The development of microglial cells in the postnatal rat retina is described using histochemical techniques for acid phosphatase and peroxidase as well as silver impregnations for microglia. On the second postnatal day, round acid phosphatase-positive macrophages appeared on the vitreal surface of retina, locating themselves close to developing blood vessels. Later, microglial precursors invaded retinal tissues, reaching the outer plexiform layer by the tenth postnatal day. In all stages studied, microglia or their precursors were peroxidase-negative. The transformation of round microglial precursors into adult ramified microglia is also described. Owing to the relation found between developing microglia and blood vessels, a vascular origin is proposed for the retinal microglial cells.

Acid Phosphatase↗
PubMed1986

Nature of macrophages in rat brain. A histochemical study.

The nature of phagocytes appearing in lesions of the central nervous system is strongly debated with a tendency to assess an exclusively hematogenous origin. We studied the origin of phagocytes appearing in a stab wound in the rat brain. Histochemical stains for acid phosphatase and peroxidase, and silver impregnation techniques were used for our study. The results obtained showed the existence of two macrophage types: endogenous microgliocytes and exogenous monocytes.

Animals↗
PubMed1985

Ultrastructure of the rat pineal stalk.

The ultrastructure of the rat pineal stalk was described. The pineal stalk contained few pinealocytes, glial cells and numerous nerve fibers. The last were mostly non-myelinated axons, although a few myelinated ones were also observed. Glial cells showed many filaments, mostly in the processes which presented a longitudinal orientation. Other more lamellar processes were found enclosing the axons. The pineal stalk became wider as it reached the body of the gland. Ultrastructurally, this wide region resembled more the pineal body. Bundles of non-myelinated nerve fibers were seen around the pineal stalk.

Actin Cytoskeleton↗
PubMed1984

Developmentally regulated expression of chimeric genes containing muscle actin DNA sequences in transfected myogenic cells.

A recombinant plasmid containing 2/3 of the rat skeletal muscle actin structural gene plus 730 bp of its 5' flanking region, spliced to the 3' end of the human epsilon-globin gene, was introduced into cells of the rat myogenic line L8. Myogenic clones carrying the actin/globin chimeric gene were isolated. In many of these clones, the expression of the gene greatly increased during differentiation (up to greater than 50-fold) and, in some clones, the amount of the chimeric gene transcripts in the differentiated cultures exceeded that of the native muscle actin gene transcripts. Furthermore, the temporal relation between differentiation of the cultures and the accumulation of the transcripts from the transferred genes was very similar to that of the native skeletal muscle actin gene, suggesting a similar mechanism of regulation. Endonuclease S1 analysis indicated a correct initiation and termination of the mRNA but suggested that a fraction of the chimeric actin/globin transcripts was not properly processed. To test whether the increased expression of the transferred gene which occurred during differentiation was determined by DNA sequences in the 5' region of the muscle actin gene, a plasmid (p alpha-CAT) containing 730 bp of the 5' flanking region of the rat skeletal muscle actin gene (plus the exon of the 5' untranslated region, and 25 bp of the first intron), spliced to the bacterial structural gene coding for chloramphenicol acetyl transferase (CAT), was constructed and introduced into L8 cells. In the majority of the isolated clones containing this plasmid, CAT activity increased many-fold during differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1984

Structure and ultrastructure of the aging rat pineal gland.

The pineal gland of rats 12-28 months old was studied with light and electron microscopes. All pineal components exhibited regressive changes of different intensity with age. In type I pinealocytes, there was a marked increase in dense bodies as well as the occasional appearance of wide cell profiles full of vesicles. Type II pinealocytes showed nuclear infoldings and cytoplasmic deposits of lipofuscin. Pineal stroma displayed an increase in connective tissue fibers, both collagen and oxytalan, as well as remains of basement membranes and other materials of unknown nature. Calcareous concretions were also found, mostly in the pineal capsule. All regressive changes were more intense with increasing age.

Aging↗
PubMed1984

Postnatal evolution of the rat pineal gland: light microscopy.

The postnatal development and morphology of the adult albino rat pineal gland was studied from one day up to ten months of age. During postnatal life there was a marked increase in gland and pinealocyte volume, more intense during the first 45 days. After ten days, the differences in nuclear morphology of parenchymal cells showed two different types of pinealocyte. The characteristic adult arrangement of pinealocytes in cords and pseudo-rosettes was observed after 15-20 days. After 75 days there was a progressive increase in the number of connective tissue fibres.

Aging↗
PubMed1984

Ultrastructure of the pineal gland in the adult rat.

The ultrastructure of the rat pineal gland was studied from 75 days until 10 months of age. Type I pinealocytes of young adults showed nuclei with dispersed chromatin, numerous infoldings of the nuclear envelope and well developed nucleoli. The cytoplasm displayed many mitochondria and clusters of smooth endoplasmic reticulum. With increasing age, there was a clear increase in the number of dense bodies or lysosomes in the Type I pinealocyte. The changes in the Type II pinealocytes with age were mainly in nuclear shape and in the appearance of lipofuscin granules.

Aging↗
PubMed1983

Postnatal development of cell types in the rat pineal gland.

The morphological development of the rat pineal gland has been studied from 1 to 60 days of age. During the first days, undifferentiated cells (pinealoblasts) with scanty cytoplasm and frequent mitotic figures were observed. The differentiation of cell types (Types I and II pinealocytes) began on the third day after birth and was completed by days 15-20. At 3 days of age, nerve fibres were first observed, both in the connective spaces and in the parenchyma. After 5 days, an important hypertrophy of pinealocytes began, mostly Type I, which continued until 60 days of age. After 45 days, all the ultrastructural features described in the adult pineal gland were already present. The findings are discussed.

Animals↗
PubMed1983

Oxytalan fibres in the rat pineal gland.

The present study shows the existence of oxytalan fibres in the connective tissue spaces of the rat pineal gland. The identification of these fibres with light microscopy is based on their ability to stain with aldehyde-fuchsin and orcein after oxidation with peracetic acid. Using the electron microscope, oxytalan fibres appear as bundles of fibrils of 12-15 nm without transverse striation. Oxytalan fibres increase with age, being most abundant in the old rat.

Aging↗
PubMed1981

Ultrastructural study of the embryonic development in the rat pineal gland.

The ultrastructure of the albino rat embryo pineal gland was studied from day 13 of development through birth. In the first stages (13-16.5 days of development) the pineal evagination presents a barely differentiated epithelium. From 17 days onward the transformation of the pineal gland from a tubular evagination into a compact organ occurs. The obliteration of the recess takes place by means of two mechanisms: (a) multiple foldings of the epithelium which determine an approximation and fusion of the walls of the recess, and (b) occupation of the lumen by cells extruded from the pineal epithelium. Embryos of 18-21 days of gestation still show remains of the pineal recess. From day 16.5 onward elements of the pineal parenchyma have been found outside the pineal epithelium contour. They contact with the mesenchymal cells without a basal lamina separating both elements. Day 20 marks the beginning of recognizable differentiation of pineal cellular types. However, in the newborn rat these types are not yet clearly established.

Animals↗
PubMed1981

Embryonic development of the rat pineal gland.

The embryonic development of the albino rat pineal gland has been studied from day 13 of development until birth. The first pineal anlage appears as a midline evagination of the diencephalic roof, which soon adopts a tubular morphology. At 17 days, the disappearance of the pineal recess begins, along with the transformation of the gland into a solid organ. The latter is mainly achieved by an infolding and thickening of the dorsal recess wall, from which derives most of the future pineal parenchyma. Blood vessels are mainly derived from the vessels found in the dorsal surface of the pineal gland.

Animals↗
PubMed1980

Ultrastructural study of the post-hatching evolution of the pineal gland of the chicken (Gallus gallus).

There is a marked evolution in the ultrastructure of the chicken pineal gland after hatching. The typical large follicular cavities that are visible just after hatching disappear with age, giving the pineal a large number of small-caliber cavities which are practically filled by the prolongations of the pinealocytes. This gives the organ an apparently solid aspect. There are still two large cell types in the follicular wall: the A and B pinealocytes, with the B type being considerably more abundant.

Aging↗
PubMed1979

Mastocytosis with skeletal and gastrointestinal involvement in infancy. Two case reports and a review of the literature.

Two cases of mastocytosis with skeletal involvement in children three and six months old are reported. Bone lesions, either sclerotic or lytic, were encountered in their skeletal surveys. Gastrointestinal lesions in children with mastocytosis are exceedingly rare; in addition to skeletal lesions, one of our patients had a large duodenal ulcer. The diagnosis of mastocytosis was established by skin biopsy in both patients. A review of the literature is also presented.

Biopsy↗
PubMed1979

Ultrastructural study of the embryonic development of the pineal gland of the chicken (Gallus gallus).

The authors studied the embryonic development of the pineal gland of the chicken with the electron microscope. The denomination of 'pinealoblasts' was given to the undifferentiated cells which form the primitive pineal outline. In the wall of the pineal cavities, the follicular and parafollicular zones were distinguished; these are formed by type A and type B pinealocytes, the B type being much more abundant. The degenerated cells are constant in the pineal throughout its embryonic development, but much more abundant in the early phases.

Animals↗