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Biomedical subjects

E E Daniel

Publications and source records attributed to E E Daniel.

At least 19 recordsLinked to original sources
PubMed1979

Ultrastructural basis for maintenance and termination of pregnancy.

Myometrial tissues from guinea pigs, sheep, and human subjects at various stages of gestation and postpartum were quantitatively examined in the electron microscope for the presence of gap junctions between muscle cells. Gap junctions were found in tissues from guinea pigs and sheep which were being delivered or ready to be delivered and in tissues taken immediately post partum. Gap junctions were also present in 19 tissues obtained from 69 women undergoing elective or emergency cesarean section for a variety of reasons. The frequency of their occurrence varies in relation to the presence or absence of labor and other conditions. We propose that gap junctions are required for effective muscle contractions leading to termination of pregnancy in all animals, including human beings. The absence of gap junctions throughout gestation may be necessary for maintenance of pregnancy and the premature appearance of the cell contacts may lead to premature labor.

Animals↗
PubMed1979

Prostaglandins and myogenic control of tension in lower esophageal sphincter in vitro.

Active tension is produced by the lower esophageal sphincter (LES) of North American opossum in vitro by a myogenic mechanism. Strips of LES, but not those from the esophageal body, contracted to prostaglandin (PG)F2 alpha, stable expoxymethano derivatives of PGH2 and to thromboxane B2. Stable endoperoxides were more than 500 times more potent than PGF2 alpha. PGI2 and 6-keto PGF1 alpha were weak relaxants of LES strips. LES strips transformed arachidonic acid into contractile substances. This transformation was prevented by agents which interfere with PG synthesis by inhibiting cyclo-oxygenase [indomethacin (IDM), 5,8,11,14-eicosatetraynoic acid (ETA) or thromboxane synthetase [imidazole]. Tranylcypromine 500 microgram/ml also inhibited contractions to arachidonic acid. These agents also reduced muscle tone, so that endogenous PG formation may contribute to active tension in the LES. ETA and IDM increased tone before inhibiting it, and this effect was prevented by prior treatment with ETA or imidazole. There may also be an endogenous PG which inhibits LES tone. The possibility that this may be PGI2 is discussed.

Animals↗
PubMed1979

Role of endogenous prostaglandins in regulating the tone of opossum lower esophageal sphincter in vivo.

The role of prostaglandins in maintenance of basal myogenic tone of the lower esophageal sphincter (LES) of opossum has been studied in vivo. Intra-arterial infusion of arachidonic acid decreased LES tone, and this was inhibited by intravenous indomethacin (IDM) or intra-arterial 5,8,11,14-eicosatetraynoic acid (ETA). Alone these drugs did not reduce LES tone except transiently. In addition they did not affect relaxation of the LES to distention of a balloon located proximal to it or inhibit the "off" contractions of esophageal body and LES pressure which followed balloon deflation. Spontaneous oscillations of LES pressure were increased with IDM. Thus prostaglandin synthesis plays no essential role in maintenance of resting LES tone or in functioning of non-adrenergic inhibitory nerves in the esophagus in vivo. Endogenous inhibitory prostaglandins might reduce LES tone if synthesized in increased amounts.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1979

Electrical coupling in rat myometrium during pregnancy.

Gap junctions were found in rat myometrium only during parturition of abortion. A comparison was made between the values of the length constants obtained from longitudinally cut strips of rat myometrium at the midterm stage of pregnancy and during parturition. No significant difference was found between these values. No significant difference was found between length constants measured in myometrium from rats near term (22 days) and those during parturition, or between midterm myometrium and myometrium taken from animals aborting at midterm following ovariectomy. It was concluded that the appearance of gap junctions in parturient myometrium does not alter the spread of passive current in the longitudinal axis of the cells in these tissues. It is suggested that gap junctions are not required for spread of passive current, and that other structures may provide an alternate path.

Animals↗
PubMed1979

Electrical coupling in the circular muscles of dog jejunum.

Two distinct layers of circular muscle have previously been demonstrated in dog jejunum, the main circular layer containing many gap junction contacts, and an inner dense muscle layer where no gap junctions have been found. Length constants were determined for these muscle layers and no significant difference was found between these values. The main circular muscle cells had lower membrane potentials and may have had abnormally low space constants owing to injury. It was concluded that the absence of gap junctions in the inner dense layer does not reduce the spread of passive current as might be expected of electrically isolated cells, and it is suggested that an alternate pathway for passive current exists in this layer.

Animals↗
PubMed1979

Prostaglandins and tetrodotoxin-insensitive relaxation of opossum lower esophageal sphincter.

Field stimulation with pulses of 0.5 or 5 ms relaxed isolated strips of lower esophageal sphincter (LES) of the opossum; only responses to 0.5-ms pulses were inhibited by tetrodotoxin. Black widow spider venom prevented relaxation to both stimuli; thus both stimuli may release nonadrenergic inhibitory mediator. Isoproterenol, but not PGEs or ATP, was a consistent relaxant of LES. PGF2alpha (approximately 1 microgram/ml) and stable endoperoxides (approximately 10 ng/ml) stimulated LES muscle. Doses of indomethacin (IDM) or 5,8,11,14-eicosatetraynoic acid (ETA), which inhibited contractions to arachidonic acid increased then abolished LES tone, inhibited relaxations to 5-ms pulses and less effectively to 0.5-ms pulses. Inhibition of relaxation preceded loss of tone. Tone could be restored by carbachol, PGEs, or PGF2alpha and relaxation after IDM but not ETA was also restored. Prostaglandins may participate in functioning of nonadrenergic inhibitory nerves and in maintaining sphincter tone. Cells that did not appear to be smooth muscle were in gap junction contact with smooth muscles and closely apposed to nerves with small agranular vesicles. A role for these structures, which are postulated to be interstitial cells, in tetrodotoxin-insensitive prostaglandin-related release of nonadrenergic inhibitory mediator was proposed.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1979

Role of Ca2+ in genesis of lower esophageal sphincter tone and other active contractions.

The effects of absent or low Ca2+ (0.5 mM), verapamil, nifedipine, Na nitroprusside, theophylline, La2+, and ethanol on basal active tension (tone), "off" contractions, and carbachol contractions were studied in opossum lower esophageal sphincter strips. Incubation in Ca2+-free Ringer (0.1 mM EGTA) abolished tone and contractions. Low Ca2+, verapamil, nifedipine, and theophylline depressed tone more rapidly than "off" contractions. Only verapamil and nifedipine depressed carbachol contractions. Na nitroprusside rapidly depressed tone but left contractions unchanged. La3+ at 1 X 10(-3) M behaved like Ca2+-free incubation but produced sustained contractions with muscle stimulation. Ethanol depressed "off" contractions more than tone and did not affect carbachol-induced contractions. These results suggest that tone probably results from inward leak of Ca2+, whereas "off" contractions depend on release of Ca2+ sequestered in the cell by a mechanism not immediately dependent on increased Ca2+ influx. Carbachol may increase Ca2+ influx as well as utilize sequestered Ca2+. Nifedipine and verapamil may act to block both resting and stimulated Ca2+ influx. Na nitroprusside may act by increasing Ca2+ efflux. Ethanol may act by decreasing the availability of sequestered Ca2+ or by inhibiting the function of a mediator responsible for "off" contractions.

Animals↗
PubMed1979

Abnormal biochemistry of vascular smooth muscle plasma membrane as an important factor in the initiation and maintenance of hypertension in rats.

Tissue wet weight as well as total protein content, 5'-nucleotidase activity, alkaline phosphatase activity and Ca2+ accumulation associated with a plasma membrane fraction isolated from spontaneous hypertensive rats (SHR) and rats with deoxycorticosterone (DOC) induced hypertension were investigated. Enhanced alkaline phosphatase activity and reduced ATP-dependent Ca2+ accumulation preceded the development of hypertension in SHR and these effects were reversed by DOC withdrawal followed by lowering of blood pressure in DOC hypertension. Increased arterial tissue wet weight and 5'-nucleotidase occurred only at the later stage of hypertension in SHR and the increased tissue wet weight was not reversed by DOC withdrawal in DOC hypertension. These observations suggest that enhanced alkaline phosphatase and reduced ATP-dependent Ca2+ uptake may play a significant role in initiating hypertension, while increased arterial wet weight and 5'-nucleotidase activities may participate in the maintenance of hypertension.

Adenosine Triphosphate↗
PubMed1979

Calcium regulation in the myometrium of pregnant sheep.

Fractionation of pregnant sheep myometrium has been carried out and the fractions obtained analysed for their marker enzyme content and Ca2+ transporting properties. A fairly pure mitochondrial fraction and a very pure plasma membrane fraction were obtained. Both fractions could accumulate Ca2+ in the presence of ATP but the mechanisms were different, mitochondrial uptake had a high capacity and was inhibited by azide. Plasma membrane uptake was of low capacity and unaffected by azide. The effect of oxalate on plasma membrane suggests that there is an outwardly directed Ca2+ pump in the myometrial cell membrane. Both mitochondria and plasma membrane may be important in the Cas2+ accumulation of relaxation in this muscle.

Animals↗
PubMed1978

Localization of the oxytocin receptor in the plasma membrane of rat myometrium.

The distribution of [3H]oxytocin binding sites among various subcellular fractions of rat myometrium paralleled the distribution of 5'-nucleotidase, a plasma membrane marker enzyme, but not of NADPH-cytochrome c reductase or succinate-cytochrome c reductase, which are endoplasmic reticulum and mitochondrial marker enzymes respectively. [3H]Oxytocin binding to the most enriched plasma membrane fraction showed the degree of selectivity with respect to hormone analogues that is expected for the oxytocin receptor. The binding of oxytocin to this fraction showed an apparent Kd of 1.98 X 10(-9) M and a capacity of 1.28 pmol mg-1. It is concluded that the oxytocin receptor is located on the plasma membrane of the smooth muscle cells of the rat uterus.

Animals↗
PubMed1978

Formation of gap junctions by treatment in vitro with potassium conductance blockers.

Gap junctions were regularly seen in thin sections of canine tracheal smooth muscle incubated in vitro. Their number was increased in tissued exposed in vitro to either of two potassium conductance blockers, tetraethylammonium (TEA) and 4-aminopyridine (4-AP), and at the same time the muscles became mechanically active, with spontaneous contractions. The presence of gap junctions in this smooth muscle may provide one basis for cell-to-cell coupling, and their increase after TEA- and 4-AP-treatment could account for a decreased junctional resistance between cells, contributing to a longer space constant. However, an increase in gap junctions was not sufficient to change the behavior of trachealis smooth muscle from multiunit to single-unit type. Gap junctions in increased numbers persisted after washout of 4-AP, which caused inhibition of spontaneous contractions, and despite inhibition of the contractile effects of 4-AP by atropine. The rapid induction of gap junction formation was not dependent on de novo synthesis of protein. The fact that the number of gap junctions can be increased by chemical agents has important implications for control of their formation and provides a tool for analysis fo their role in cell-to-cell coupling.

Aminopyridines↗
PubMed1978

The generation and conduction of activity in smooth muscle.

Smooth muscle, especially gastrointestinal smooth muscle, spontaneously generates oscillatory electrical activity that can control contractions in time and space by altering excitability. The origin and ionic mechanisms underlying these electrical control activities are still controversial, but they behave as coupled relaxation oscillators and they control muscle excitability. Normally, contractions are produced by the addition, during the depolarized phase of the oscillations, of further depolarization by acetylcholine or other means. Pharmacologists who wish to study drug actions on such muscles must be aware of the possibility that drug effects may be determined by these oscillations and may influence contractions by affecting these oscillations as well as by releasing, mimicking, or inhibiting the effects of nerve mediators or by affecting excitation-contraction coupling. Also the use of simplified organ bath preparations may eliminate or alter these control potentials so that results in vitro may not apply in vivo.

Animals↗