These studies indicate that tetraethylammonium (TEA) is transported by saturable processes from bath to lumen and lumen to bath in isolated, perfused snake (Thamnophis spp.) proximal renal tubules and that the unidirectional flux from bath to lumen (Jᵇ¹(TEA)) exceeds the unidirectional flux from lumen to bath (J¹ᵇ (TEA)) at all TEA concentrations studied. In order to examine the transport process further, the effects of N¹-methylnicotinamide (NMN), temperature, sodium cyanide, and the removal of Na⁺ on TEA transport were studied. Steady-state Jᵇ¹(TEA) (103.2 ± 1.1 fmoles min⁻¹ mm⁻¹ at {TEA}(b) = 8.1 μM) was inhibited by 50% at {NMN}(b) = 4.0 mM. When TEA and NMN were present in the lumen, J¹ᵇ (TEA) was depressed initially (T < 8 min). However, at steady-state, the presence of NMN in the lumen appeared to stimulate J¹ᵇ (TEA). This suggests a trans-stimulation effect of NMN on J¹ᵇ (TEA). During some flux experiments tubules were perfused at room temperature (24°C) and then cooled to 2.8°C. Jᵇ¹(TEA) decreased approximately 25% when compared to control values. This effect was reversible. Other tubules were perfused in the presence of 2.5 mM sodium cyanide in the perfusate and bath. Cellular concentrations of TEA dropped from 67 to 27 times the bath concentration during Jᵇ¹(TEA) measurements and from 21 to 6 times the mean luminal concentration during J¹ᵇ (TEA) measurements. This indicates that little if any intracellular binding of TEA occurs, as passive accumulation should be 16.1 times the bath or lumen TEA concentration (assuming a -70 mV PD). To determine if TEA transport was dependent on the presence of Na⁺, Na⁺ in the bath and perfusate solutions was replaced isosmotically by sucrose. Jᵇ¹(TEA) was not significantly changed in the absence of Na⁺. J¹ᵇ (TEA) decreased to 56% of control in the absence of Na⁺. This effect was reversible. Thus, J¹ᵇ (TEA) is Na⁺-dependent and Jᵇ¹(TEA) is not. These data suggest that the transport characteristics of the carrier for TEA at the luminal and peritubular membranes of the distal-proximal tubules of garter snakes are dissimilar.

by Lee Heung Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves 189-203.

by Kareen Kar-lit Wong. / Thesis (M.Phil.)--The Chinese University of Hong Kong. / Bibliography: l. 134-146.

School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, 2017 / Snakes have often been proposed as ideal model organisms for studying digestive physiology. This is due to their easily–measureable and extreme changes in their digestive tracts in response to feeding, when compared to other vertebrates. Some species display extreme physiology regulation in response to feeding, a system known as digestive down-regulation. This regulation allows them to down-regulate their digestive tracts during their long fasting periods, which allows them to save energy. In response to feeding, they up-regulate their digestive tracts to a functional level, resulting in a significant increase in the size of the digestive organs during digestion. These changes have been found to be most noticeable in certain ambush foraging snakes. In contrast, actively foraging snakes appear to not display as extreme changes in response to feeding and keep their digestive tracts in a constant state of readiness. However it is not known if this pattern exists in all species and previous methods of classifying the digestive physiology have proven to be expensive, difficult and time consuming. My study aimed to investigate if museum specimens could be used as a cheap and quick method of classifying the characteristics of the digestive physiology within a species. I measured the dimensions of several organs from museum specimens from 13 species of southern African snakes, as well as recorded the relative size of the meal and month of capture. I compared measurements between postprandial and fasting individuals from each species as well as between individuals from each species with the same feeding state to assess whether they were able to down-regulate their digestive systems when not digesting. While the different foraging strategies appeared to be linked to differences in organ morphology, the presence of down-regulation was not clear-cut. No significant differences in organ size between feeding states were found within each species, and very few significant differences were found between species. Few correlations with organ size to meal size or seasonality were found. This suggests that the museum specimens are not suitable for determining digestive physiology in snakes, probably due to the poor quality of the specimens. I therefore recommend the use of freshly obtained samples as a suitable comparison rather than the use of museum specimens. / MT2017