Ontogeny of secretory function and cholecystokinin binding capacity in immature rat pancreas

Isolated acini were prepared from the pancreas of immature rats (age less than 1 hr. - 48 hrs) in order to study the development of the secretory process. The ultrastructural integrity of the acinar cells was maintained after digestion and stimulation with secretagogues. Acini prepared from rats aged 24 - 48 hours responded to both CCK-8 and carbachol with significant increases in amylase release. Although typical biphasic dose response curves were obtained, the curves were shifted to the right by 1 - 2 log units, compared to the responses of adult acini. At ages younger than 24 hours, acini were insensitive to secretagogues but were sensitive to the calcium ionophore A23187. CCK receptors were virtually absent from membranes prepared from newborn pancreases, but binding of CCK, although small, was measurable at 12 hours and slowly increased up to 48 hours. A greater amount of binding was seen at 72 hours, which appeared constant up to 14 days. At 21 days, adult levels of binding were found. These results confirm previous studies that the rat pancreas is insensitive to secretagogues in the first 24 hours of life. After age 24 hours the secretory process is intact but less sensitive to secretory agents than the more mature pancreas. In the case of CCK, this may be due to lesser numbers of CCK receptors and/or affinity of CCK for its receptor.     

Bioengineering in development of the hybrid artificial pancreas

The hybrid artificial pancreas for treatment of diabetes consists of insulin-secreting pancreatic tissue which is surrounded by a membrane that protects the tissue from rejection by the immune system following implantation. In this paper, we review the alternative therapeutic approaches for diabetes under study and then discuss the technical requirements that must be met by a hybrid device useful to humans. Previous work on intravascular and extravascular immunoisolation devices is reviewed from the standpoint of these requirements, and three critical unresolved issues are discussed: biocompatibility, oxygen supply limitations, and prevention of immune rejection.     

Effect of pressure on [3H]GABA release by synaptosomes isolated from cerebral cortex

High hydrostatic pressure has been shown to produce neurological changes in humans which manifest, in part, as tremor, myoclonic jerks, electroencephalographic changes, and convulsions. This clinical pattern has been termed high-pressure nervous syndrome (HPNS). These symptoms may represent an alteration in synaptic transmission in the central nervous system with the inhibitory neural pathways being affected in particular. Since gamma-aminobutyric acid (GABA) transmission has been implicated in other seizure disorders, it was of interest to study GABAergic function at high pressure. Isolated synaptosomes were used to follow GABA release at 67.7 ATA of pressure. The major observation was a 33% depression in total [3H]GABA efflux from depolarized cerebrocortical synaptosomes at 67.7 ATA. The Ca2+-dependent component of release was found to be completely blocked during the 1st min of [3H]GABA efflux with a slow rise over the subsequent 3 min. These findings lead us to conclude that high pressure interferes with the intraterminal cascade for Ca2+-dependent release of GABA.     

The action of hydrogen peroxide on paired pulse and long-term potentiation in the hippocampus

The action of a reactive oxygen intermediate, that is, hydrogen peroxide (H2O2) on modulation of synaptic transmission was examined in the hippocampal brain slice preparation. Microinjection of H2O2 into the apical dendritic region of the CA1 pyramidal cells produced no change in either the pattern or amplitude of paired pulse facilitation compared to saline injection (control). Long term potentiation (LTP), induced by high frequency stimulation of homosynaptic inputs, however, was blocked by microinjection of H2O2 into the dendritic tree. LTP was seen in only 2 out of 10 slices investigated when treated with H2O2 while LTP was seen in 4 out of 5 slices when saline injected. The results suggest that a reactive oxygen intermediate can selectively modify synaptic mechanisms in the hippocampus.     

Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.      

Basolateral plasma membrane localization of ouabain-sensitive sodium transport sites in the secretory epithelium of the avian salt gland

The distribution of Na+ pump sites (Na+-K+-ATPase) in the secretory epithelium of the avian salt gland was demonstrated by freeze-dry autoradiographic analysis of [(3)H] ouabain binding sites. Kinetic studies indicated that near saturation of tissue binding sites occurred when slices of salt glands from salt-stressed ducks were exposed to 2.2 μM ouabain (containing 5 μCi/ml [(3)H]ouabain) for 90 min. Washing with label-free Ringer's solution for 90 min extracted only 10% of the inhibitor, an amount which corresponded to ouabain present in the tissue spaces labeled by [(14)C]insulin. Increasing the KCl concentration of the incubation medium reduced the rate of ouabain binding but not the maximal amount bound. In contrast to the low level of ouabain binding to salt glands of ducks maintained on a freshwater regimen, exposure to a salt water diet led to a more than threefold increase in binding within 9-11 days. This increase paralleled the similar increment in Na+-K+-ATPase activity described previously. [(3)H]ouabain binding sites were localized autoradiographically to the folded basolateral plasma membrane of the principal secretory cells. The luminal surfaces of these cells were unlabeled. Mitotically active peripheral cells were also unlabeled. The cell-specific pattern of [(3)H]ouabain binding to principal secretory cells and the membrane-specific localization of binding sites to the nonluminal surfaces of these cells were identical to the distribution of Na+-K+-ATPase as reflected by the cytochemical localization of ouabain-sensitive and K+-dependent nitrophenyl phosphatase activity. The relationship between the nonluminal localization of Na+-K+-ATPase and the possible role of the enzyme n NaCl secretion is considered in the light of physiological data on electrolyte transport in salt glands and other secretory epithelia.     

Diurnal variability in a fish assemblage of a Bahamian coral reef

Synopsis Variation in the diurnal composition of a fish assemblage of a Bahamian coral reef was investigated by comparing visual counts of fishes taken along a 100 × 4 m wide fixed transect at four times: 0900, 1200, 1500 and 1800 hours during the summer of 1979. One sample per day was obtained at each time period over a span of 20 consecutive days. Forty-two species were recorded in these samples, with 25 occurring frequently enough to permit statistical analysis of diurnal variations in abundance. Of the 25 species compared, nearly one fourth (6 species) displayed significant variation in abundance patterns among the four time periods tested. It is suggested, because of the strong possibility of bias which might otherwise be introduced because of these variations, that repetitive quantitative visual censusing of coral reef fishes be undertaken at about the same time each day.     

Identification of high affinity endothelin-1 receptor subtypes in human tissues.

Two subtypes of the high affinity endothelin-1 (ET-1) receptor were identified in human tissue, and were distinguished by their differential affinities for sarafotoxin S6c (S6c). Uterus contains mostly the ETA subtype, with low affinity for S6c (Ki greater than 7300 nM), while the predominant subtype in hippocampus is ETB, with high affinity for S6c (Ki = 0.25 nM). These subtypes also have different affinities for [Ala1,3,11,15]-ET-1, which was found to be ETB selective. The two subtypes distinguished by these ligands in human tissue correspond to the subtypes previously identified in rat. Differential stimulation of phosphatidyl inositol turnover in rat tissue slices by ET-1 and S6c indicates that both ETA and ETB subtypes represent functional receptors.