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PubMed1996

Plasma triglyceride and beta-hydroxybutyric acid levels in red-sided garter snakes (Thamnophis sirtalis parietalis) at emergence from hibernation.

Measurement of plasma levels of triglycerides and beta-hydroxybutyric acid in females and males of the red-sided garter snake (Thamnophis sirtalis parietalis) suggest that the former may provide a useful physiological marker of condition. Levels of triglycerides at emergence from hibernation during a month of natural aphagia were significantly greater in females than in males and she-males, a subset of the male population that mimics females. Higher levels of triglycerides in the females may be attributed to their greater body mass per unit length, which was correlated with the level of triglycerides. Plasma triglyceride levels declined in females within one month of emergence, at the onset of feeding, and were unrelated to mating.

3-Hydroxybutyric Acid↗

PubMed1990

Two subclasses of EGF receptors in the human pancreatic cancer cell lines CAPAN-1 and MIA PaCa-2.

The existence of different classes of EGF receptors in human pancreatic cancer cells has yet not been determined. EGF binding to two cancer cell lines (CAPAN-1 and MIA PaCa-2) was studied. Two classes of EGF binding sites were characterized. The first class of EGF binding sites demonstrated a high affinity and low capacity for EGF, with a Kd of 0.25 +/- 0.11 nM, close to the concentration of EGF suggested to be present in human pancreatic juice. The second class of EGF binding sites had a lower affinity and a higher capacity for EGF, with Kd of 1.78 +/- 0.61 nM. The total number of EGF binding sites was about 40,000/cell. Treatment of the cells with a phorbol ester, TPA, caused a complete loss of the high affinity binding sites and also caused a decrease in the concentration of the lower affinity binding sites present on the cells. Interestingly, with the increasing age of the cells, the concentration of both the high and low affinity EGF binding sites was significantly decreased. In the presence or absence of fetal calf serum, EGF, at concentrations higher than 1.10(-10)M, exerted a dose-dependent mitogenic effect on the growth of the pancreatic cancer cells in culture. These data demonstrate the existence of two classes of binding sites for EGF on some human pancreatic cancer cells and a possible role of EGF in the growth of pancreatic tumors.

Cell Division↗

PubMed2005

Effect of prolonged inactivity on skeletal motor nerve terminals during aestivation in the burrowing frog, Cyclorana alboguttata.

This study examined the effect of prolonged inactivity, associated with aestivation, on neuromuscular transmission in the green-striped burrowing frog, Cyclorana alboguttata. We compared the structure and function of the neuromuscular junctions on the iliofibularis muscle from active C. alboguttata and from C. alboguttata that had been aestivating for 6 months. Despite the prolonged period of immobility, there was no significant difference in the shape of the terminals (primary, secondary or tertiary branches) or the length of primary terminal branches between aestivators and non-aestivators. Furthermore, there was no significant difference in the membrane potentials of muscle fibres or in miniature end plate potential (EPP) frequency and amplitude. However, there was a significant decrease in evoked transmitter release characterised by a 56% decrease in mean EPP amplitude, and a 29% increase in the failure rate of nerve terminal action potentials to evoke transmitter release. The impact of this suite of neuromuscular characteristics on the locomotor performance of emergent frogs is discussed.

Animals↗

PubMed2002

Effect of aestivation on muscle characteristics and locomotor performance in the green-striped burrowing frog, Cyclorana alboguttata.

The Green-striped burrowing frog, Cyclorana alboguttata survives extended drought periods by burrowing underground and aestivating. These frogs remain immobile within cocoons of shed skin and mucus during aestivation and emerge from their burrows upon heavy rains to feed and reproduce. Extended periods of immobilisation in mammals typically result in muscle atrophy and a decrease in muscle performance. We examined the effect of aestivation and hence prolonged immobilisation, on skeletal muscle mass, in vitro muscle performance, and locomotor performance in C. alboguttata. Frogs were aestivated in soil for 3 months and were compared with control animals that remained active, were fed, and had a continual supply of water. Compared to the controls, the wet mass of the gastrocnemius, sartorius, gracilus major, semimembranosus, peroneus, extensor cruris, tibialis posticus and tibialis anticus longus of aestivators remained unchanged indicating no muscle atrophy. The in-vitro performance characteristics of the gastrocnemius muscle were maintained and burst swimming speed was unaffected, requiring no recovery from the extended period of immobilisation associated with aestivation. This preservation of muscle size, contractile condition and locomotor performance through aestivation enables C. alboguttata to compress their life history into unpredictable windows of opportunity, whenever heavy rains occur.

Animals↗

PubMed2001

Mitochondria-rich cells in gills and skin of an African lungfish, Protopterus annectens.

We used scanning electron microscopy, the vital dye DASPEI and an antibody to the inner mitochondrial membrane to study the presence and localisation of mitochondria-rich cells in the gills and skin (opercular, dorsal and ventral) of the lungfish Protopterus annectens in its free-swimming conditions and at the beginning of aestivation. In the free-swimming period, the gills were short and thick and the pavement cells were extremely large (30-40 microns). The mitochondria-rich cells, which were distributed in the secondary and primary epithelium, occurred as two morphologically different types, i.e. elongated and oval, similar to the alpha and beta chloride cells of fresh water teleosts. In the skin, only one type of mitochondria-rich cells was found, resembling the alpha chloride cells. All the mitochondria-rich cells distributed in the gills and skin were labelled with anti Ca(2+)-ATPase serum indicating the possible uptake of Ca2+ at freshwater chloride cell level. At the start of aestivation, the skin and gills were covered by a thick layer of mucus and the epithelium of the gills was reduced. The mitochondria-rich cells were almost completely covered by the pavement cells.

Animals↗

PubMed2004

Incidence of diapause varies among populations of Daphnia pulicaria.

Dormancy is a common way in which organisms survive environmental conditions that would be lethal to the active individual. However, while dormant, individuals forego reproduction. Hence theory suggests an optimal time in which to enter dormancy, depending on risks associated with both remaining active and entering dormancy. When these relative risks differ among habitats, dormancy strategies are predicted to vary as well. For freshwater zooplankton, it has been suggested that sensitivity to the cues that initiate dormancy should be selected against when females have the opportunity to remain in the water column year round. We tested this prediction with 12 populations of lake-dwelling Daphnia pulicaria (Crustacea: Cladocera). Differences among lakes in basin morphometry, predators and resources create a gradient of risk for Daphnia in the water column. Some populations persist in high numbers year round while others are abundant only in spring. We used this difference in persistence ability as an estimate of risk in the water-column. For 3 years of field sampling we found consistent differences among the lake populations in the incidence of dormancy. In some populations, only a small fraction of females switched to producing dormant eggs each year whereas in others the majority of eggs produced in the late spring were dormant. In general, populations that experienced predictably low abundances in the active form exhibited higher incidence of dormancy than did populations that persisted in high abundance year round, but there were exceptions. Our results confirm that the incidence of dormancy varies considerably among populations in a fashion consistent with general theory, but suggest that persistence in the water column is not the sole predictor of the diapause strategy found in any particular lake.

Adaptation, Physiological↗

PubMed1983

Presence of VIP receptors in a human pancreatic adenocarcinoma cell line. Modulation of the cAMP response during cell proliferation.

It is known that the human exocrine pancreas responds to secretin stimulation more than does VIP, a structurally related peptide. We looked for the receptors for those polypeptides in a human pancreatic cancer cell line grown in culture and in nude mice. By analysing the cAMP responses and the 125I-VIP binding we found VIP receptors with a KD of 1.5 10(-9) M. Secretin stimulates the adenylate cyclase through the VIP receptor sites with a KD of 1.7. 10(-6) M. We noted also that during cell proliferation in culture there was about a 5 fold increase of the cAMP response to VIP.

Adenocarcinoma↗

PubMed1972