Biomedical subjects

C D Logsdon

Publications and source records attributed to C D Logsdon.

78 records · Page 5Linked to original sources

PubMed1983

Pancreatic acini in short-term culture: regulation by EGF, carbachol, insulin, and corticosterone.

To define the hormonal regulation of the exocrine pancreas, acini were maintained for 24 h in suspension culture under various conditions and then examined morphologically and tested for their ability to synthesize and secrete protein. Acini cultured in the presence of 20% fetal calf serum (control conditions) retained their differentiated morphology as judged by light and electron microscopy. Under control conditions, stimulation with either cholecystokinin octapeptide (CCK8) or carbachol increased the release of amylase in a dose-dependent manner with a maximal threefold increase occurring at 200 pM CCK8 or 6 microM carbachol. Without inclusion of other factors in the medium during the culture period, the rate of protein synthesis measured in cultured acini was one-third the rate measured in freshly prepared acini. Inclusion of epidermal growth factor (EGF) (2 nM), carbachol (1 microM), or insulin (1 microM) during the culture period led to increases, whereas corticosterone (1 microM) led to decreases in functional parameters. Greatest effects were seen with a combination of EGF, carbachol, and insulin. This combination of factors led to a 160% increase over control in CCK8-stimulated amylase release and a 180% increase in [3H]leucine incorporation. These results indicate that isolated pancreatic acini can be maintained for up to 24 h and that EGF, carbachol, insulin, and corticosterone can regulate the long-term function of this tissue.

Amylases↗

PubMed1983

Epidermal growth factor binding and biologic effects on mouse pancreatic acini.

We have examined the receptor binding of radio-iodinated murine epidermal growth factor and the effects of epidermal growth factor on both amylase release and incorporation of [3H]leucine into protein in isolated adult mouse pancreatic acini in primary culture. Binding of radioiodinated murine epidermal growth factor was specific, saturable, and reversible at 37 degrees C. Analysis of competitive inhibition plots was consistent with single class of receptors with a dissociation constant of 4.0 X 10(-10) M and a binding capacity of 40,000 sites per cell. The binding of epidermal growth factor by acini was accompanied by minimal degradation of the peptide present in the medium or of that associated with the cells. Epidermal growth factor increased the basal and cholecystokinin-octapeptide-stimulated release of amylase from cultured acini with half-maximal effects at 1.5 X 10(-10) M. This effect on amylase release required a relatively long exposure to epidermal growth factor, being half-maximal after 3 h and maximal after 10 h. Epidermal growth factor also increased the incorporation of [3H]leucine into protein with a half-maximal effect at 3.0 X 10(-10) M. This effect was half-maximal after 2.5 h and maximal in 8-10 h. These data, therefore, suggest that epidermal growth factor may have a physiologic role in regulating the exocrine pancreas.

Amylases↗

PubMed1982

Fetal rabbit gastric epithelial cells cultured on floating collagen gels.

Cells were isolated from approximately 30 d fetal rabbit stomachs and cultured on floating collagen gels. Electron microscopy showed monolayers in which only one cell type persisted. These columnar cells were joined at apical borders by tight junctions and contained an extensive endoplasmic reticular network with an occasional intracellular canaliculus. They also occasionally contained what appeared to be secretory granules (mucus?), and therefore had some characteristics of all the cell types of the intact fetal stomachs, which showed oxyntic, mucous, and undifferentiated cells. In Ussing chambers with Ringer's solution on both sides, cultures developed transepithelial potential (potential difference [PD], mV, mucosa ground) = 13, resistance (resistance [R], omega - cm2) - 285, and short-circuit current (Isc, microA/cm3) = 45 (n = 7), clearly indicating that cellular polarity and junctional integrity were maintained. These transport parameters were somewhat different for intact fetal stomachs (PD = 20, R = 70, and Isc = 220 [n = 4]), which may be due to extensive folding of intact fetal stomachs or the presence of only one cell type in culture, or both. Although gastric stimulants histamine, dibutyryl cycle AMP (dbcAMP), and isobutylmethylxanthine (IMX) (a phosphodiesterase inhibitor) did not elicit H+ secretion or electrophysiological changes in monolayers or intact stomachs, 10-4 M apical amiloride caused a decrease in Isc in cultured monolayers(27%) and intact stomachs (50%). Thus, Na+ transport seems to be a significant fraction of ion transport in both preparations. This culture system may allow the study of oxyntic cell differentiation and the development of H+, Na+, and Cl- transport in the gastric musoca.

Animals↗

PubMed1982

Ionic requirements for H+ secretion and membrane elaboration in frog oxyntic cells.

We have tested whether the ions K+, Na+, or Cl- are required for either initiation or maintenance of secretory parameters of amphibian oxyntic cells. In vitro mucosal preparations were washed repeatedly in Ringer solution lacking the ion in question either before (i.e., resting tissues) or after addition of stimulants. Electrophysiology, H+ secretion, and morphology (morphometric analysis of oxyntic cells) were monitored. Na+ or K+. Stimulation of resting tissues in Na+ or K+-free solutions elicited no H+ secretion; there was only a small increase (approximately twofold) in secretory surface density (Sv) (during control Sv increased sixfold). The Na+-free effects were partially reversed by high [K+]. In secreting tissues, Na+ or K+-free solutions caused H+ secretion to decrease to zero. Gastric glands from these mucosae appeared "occluded": the gland lumen was filled with apposed apical projections of oxyntic cells. Cl-. Stimulation after Cl- removal initiated low levels of H+ secretion. Morphologically the cells either appeared normally stimulated (Sv increased eightfold) or, more rarely, took on the occluded appearance. Cl- removal from stimulated mucosae decreased H+ secretion approximately 50%, but the cells were normally elaborate. We conclude that K+ is required for the initiation of H+ secretion and the stimulated morphology change; the effects of Na+ removal are due to effects on internal [K+]; Cl- is not required. The occurrence of occluded morphology under conditions of inhibited H+ and H2O secretion indicates a role for water flow in the maintenance of stimulated morphology.

Animals↗

PubMed1981

Involvement of extracellular calcium in gastric stimulation.

We have tested whether external Ca2+ is required for either initiation or maintenance of secretory parameters, including membrane elaboration of oxyntic cells, in frog gastric mucosa. Ca2+ was removed from in vitro mucosal preparations [by washing repeatedly in Ca2+-free Ringer solution and adding 0.1 mM ethylene glycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid to the serosal solution] either before (i.e., resting tissues) or after addition of stimulants. Electrophysiology [transepithelial potential difference (PD) and resistance], morphology (morphometric analysis of transmission electron micrographs), and transport (H+ secretion) were monitored. La3+ (1 mM) was added to the mucosal solution to help maintain resistance and PD. La3+ decreased tissue shunt conductance during Ca2+-free conditions, as evidenced by a decreased mucosal-serosal flux of 22Na+, presumably by preserving tight-junction integrity. Secretion was elicited by histamine alone or in combination with dibutyryl cAMP and isobutylmethylxanthine (a phosphodiesterase inhibitor). External Ca2+ is not required for the initiation of H+ secretion or the accompanying morphological changes when the combined stimulants are used, whereas H+ secretion and the morphological change showed some Ca2+ dependency when histamine alone was used. Thus, histamine-elicited secretion seems to be more sensitive to Ca2+ removal than that brought about by the combined stimulants. Long-term effects of Ca2+-free solutions on resistance, PD, and H+ secretion can largely be explained by disruptive effects on tight junctions.

Animals↗

PubMedDate not supplied

Glucocorticoids have opposite effects on ornithine decarboxylase and cell growth in pancreatic acinar AR42J cells.

This paper reviews the relationships between the effects of glucocorticoids on rat pancreatic acinar AR42J cell polyamine levels and cellular growth and differentiation. Glucocorticoids inhibit the growth of AR42J cells. Glucocorticoids either stimulate or inhibit the formation of polyamines in a variety of cell types. Cells require polyamines for normal growth. Therefore, we tested the hypothesis that polyamines mediate the effects of glucocorticoids on AR42J cells. First, to confirm that AR42J cells required polyamines for growth we examined the effects of inhibiting ornithine decarboxylase (ODC). ODC is the most important and generally rate-limiting enzyme in the synthesis of the polyamines. As expected, the ODC inhibitor difluoromethylornithine (DFMO) inhibited AR42J cell DNA synthesis, and the addition of exogenous putrescine reversed this effect. The levels of growth inhibition by glucocorticoids and DFMO treatment were similar. Second, we examined the effects of glucocorticoids on ODC. Surprisingly, glucocorticoids increased levels of AR42J cell ODC mRNA, ODC activity, and putrescine. Glucocorticoids increased these parameters over a similar time-course as they decreased DNA synthesis. Analog specificity studies indicated that a glucocorticoid receptor mediated both the growth inhibitory and ODC stimulatory effects. Dose-response studies indicated, however, that growth inhibition was more sensitive to dexamethasone (DEX) than were ODC levels. Therefore, polyamines do not account for the effects of glucocorticoids on AR42J cell growth. In these cells, glucocorticoids have opposite and independent effects on ODC and growth.

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