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Abstract Background We describe the genome of the western painted turtle, Chrysemys picta bellii, one of the most widespread, abundant, and well-studied turtles. We place the genome into a comparative evolutionary context, and focus on genomic features associated with tooth loss, immune function, longevity, sex differentiation and determination, and the species' physiological capacities to withstand extreme anoxia and tissue freezing. Results Our phylogenetic analyses confirm that turtles are the sister group to living archosaurs, and demonstrate an extraordinarily slow rate of sequence evolution in the painted turtle. The ability of the painted turtle to withstand complete anoxia and partial freezing appears to be associated with common vertebrate gene networks, and we identify candidate genes for future functional analyses. Tooth loss shares a common pattern of pseudogenization and degradation of tooth-specific genes with birds, although the rate of accumulation of mutations is much slower in the painted turtle. Genes associated with sex differentiation generally reflect phylogeny rather than convergence in sex determination functionality. Among gene families that demonstrate exceptional expansions or show signatures of strong natural selection, immune function and musculoskeletal patterning genes are consistently over-represented. Conclusions Our comparative genomic analyses indicate that common vertebrate regulatory networks, some of which have analogs in human diseases, are often involved in the western painted turtle's extraordinary physiological capacities. As these regulatory pathways are analyzed at the functional level, the painted turtle may offer important insights into the management of a number of human health disorders.

BackgroundMild hypothermia is neuroprotective after cerebral ischemia but surgery involving profound hypothermia (PH, temperature less than 18°C) is associated with neurologic complications. Rewarming (RW) from PH injures hippocampal neurons by glutamate excitotoxicity, N-methyl-D-aspartate receptors, and intracellular calcium. Because neurons are protected from hypoxia-ischemia by anesthetic agents that inhibit N-methyl-D-aspartic acid receptors, we tested whether anesthetics protect neurons from damage caused by PH/RW.MethodsOrganotypic cultures of rat hippocampus were used to model PH/RW injury, with hypothermia at 4°C followed by RW to 37°C and assessment of cell death 1 or 24 h later. Cell death and intracellular Ca were assessed with fluorescent dye imaging and histology. Anesthetic agents were present in the culture media during PH and RW or only RW.ResultsInjury to hippocampal CA1, CA3, and dentate neurons after PH and RW involved cell swelling, cell rupture, and adenosine triphosphate (ATP) loss; this injury was similar for 4 through 10 h of PH. Isoflurane (1% and 2%), sevoflurane (3%) and xenon (60%) reduced cell loss but propofol (3 μM) and pentobarbital (100 μM) did not. Isoflurane protection involved reduction in N-methyl-D-aspartate receptor-mediated Ca influx during RW but did not involve γ-amino butyric acid receptors or KATP channels. However, cell death increased over the next day.ConclusionAnesthetic protection of neurons rewarmed from 4°C involves suppression of N-methyl-D-aspartate receptor-mediated Ca overload in neurons undergoing ATP loss and excitotoxicity. Unlike during hypoxia/ischemia, anesthetic agents acting predominantly on γ-aminobutyric acid receptors do not protect against PH/RW. The durability of anesthetic protection against cold injury may be limited.

To investigate the cellular mechanisms underlying the negative force-frequency relationship (FFR) in the ventricle of the varanid lizard, Varanus exanthematicus, we measured sarcomere and cell shortening, intracellular [Ca.sup.2+] ([[[Ca.sup.2+]].sub.i]), action potentials (APs), and [K.sup.+] or -]currents in isolated ventricular myocytes. Experiments were conducted between 0.2 and 1.0 Hz, which spans the physiological range of in vivo heart rates at 20-22[degrees]C for this species. As stimulation frequency increased, diastolic length, percent change in sarcomere length, and relaxation time all decreased significantly. Shortening velocity was unaffected. These changes corresponded to a faster rate of rise of [[[Ca.sup.2+]].sub.i], a decrease in [[[Ca.sup.2+]].sub.i] transient amplitude, and a seven-fold increase in diastolic [[[Ca.sup.2+]].sub.i]. The time constant for the decay of the [Ca.sup.2+] transient ([tau]) decreased at higher frequencies, indicating a frequency-dependent acceleration of relaxation (FDAR) but then reached a plateau at moderate frequencies and did not change above 0.5 Hz. The rate of rise of the AP was unaffected, but the AP duration (APD) decreased with increasing frequency. Peak depolarization tended to decrease, but it was only significant at 1.0 Hz. The decrease in APD was not due to frequency-dependent changes in the delayed inward rectifier ([I.sub.Kr]) or the transient outward ([I.sub.to]) current, as neither appeared to be present in varanid ventricular myocytes. Our results suggest that a negative FFR relationship in varanid lizard ventricle is caused by decreased amplitude of the [Ca.sup.2+] transient coupled with an increase in diastolic [Ca.sup.2+], which leads to incomplete relaxation between beats at high frequencies. This coincides with shortened APD at higher frequencies. action potential; calcium; diastolic [Ca.sup.2+], [IK.sub.1]; [IK.sub.r]; [I.sub.10]; reptile; sarcomere shortening doi:10.1152/ajpregu.00650.2009

Galli GLJ, Warren DE, Shiels HA. [Ca.sup.2+] cycling in cardiomyocytes from a high-performance reptile, the varanid lizard {Varanus exanthematicus). Am J Physiol Regul Integr Comp Physiol 297: R1636-R1644, 2009. First published October 7, 2009; doi: 10.1152/ajpregu.00381.2009.--The varanid lizard possesses one of the largest aerobic capacities among reptiles with maximum rates of oxygen consumption that are twice that of other lizards of comparable sizes at the same temperature. To support this aerobic capacity, the varanid heart possesses morphological adaptations that allow the generation of high heart rates and blood pressures. Specializations in excitation-contraction coupling may also contribute to the varanids superior cardiovascular performance. Therefore, we investigated the electrophysiological properties of the L-type [Ca.sup.2+] channel and the [Na.sup.+]/[Ca.sup.2+] exchanger (NCX) and the contribution of the sarcoplasmic reticulum to the intracellular [Ca.sup.2+] transient ([DELTA][[Ca.sup.2+]].sub.i]) in varanid lizard ventricular myocytes. Additionally, we used confocal microscopy to visualize myocytes and make morphological measurements. Lizard ventricular myocytes were found to be spindle-shaped, lack T-tubules, and were -190 [micro]m in length and 5-7 [micro]m in width and depth. Cardiomyocytes had a small cell volume (~2 pL), leading to a large surface area-to-volume ratio (18.5), typical of ectothermic vertebrates. The voltage sensitivity of the L-type [Ca.sup.2+] channel current (/ca), steady-state activation and inactivation curves, and the time taken for recovery from inactivation were also similar to those measured in other reptiles and teleosts. However, transsarcolemmal [Ca.sup.2+] influx via reverse mode [Na.sup.+]/ [Ca.sup.2+] exchange current was fourfold higher than most other ectotherms. Moreover, pharmacological inhibition of the sarcoplasmic reticulum led to a 40% reduction in the A[[Ca.sup.2+]]i amplitude, and slowed the time course of decay. In aggregate, our results suggest varanids have an enhanced capacity to transport [Ca.sup.2+] through the [Na.sup.+]/[Ca.sup.2+] exchanger, and sarcoplasmic reticulum suggesting specializations in excitation-contraction coupling may provide a means to support high cardiovascular performance. sarcoplasmic reticulum; electrophysiology; excitation-contraction coupling; L-type Ca channel; [Na.sup.+]/[Ca.sup.2+] exchanger doi: 10.1152/ajpregu.00381.2009.

To test the hypothesis that submergence temperature affects the distribution of the lactate load and glycogen utilization during anoxia in turtles, we sampled a variety of tissues after 7 days, 24 h, and 4 h of anoxic submergence at 5, 15, and 25[degrees]C, respectively. These anoxic durations were chosen because we found that they produced similar decreases in plasma HC[O.sub.3] (~18-22 meq/1). The sampled tissues included ventricle, liver, small intestine, carapace, and the following muscles: flexor digitorum longus, retrahens capitis, iliofibularis, and pectoralis. Shell and skeleton sequestered 41.9, 34.1, and 26.1% of the estimated lactate load at 5, 15, and 25[degrees]C. The changes in plasma [Ca.sup.2+] and [Mg.sup.2+,] relative to the estimated lactate load, decreased with increased temperature, indicating greater buffer release from bone at colder temperatures. Tissue lactate contents, relative to plasma lactate, increased with the temperature of the submergence. Glucose mobilization and tissue glycogen utilization were more pronounced at 15 and 25[degrees]C than at 5[degrees]C. We conclude that, in slider turtles, the ability of the mineralized tissue to participate in the buffeting of lactic acid during anoxia is inversely related to temperature, causing the lactate burden to shift to the tissues at warmer temperatures. Muscles utilize glycogen during anoxia more at warmer temperatures. anoxia; lactic acidosis doi: 10.1152/ajpregu.00174.2006

We aimed to determine how increases in intracellular H+ and inorganic phosphate (Pi) to levels observed during anoxic submergence affect contractility in ventricular muscle of the anoxia-tolerant Western painted turtle, Chrysemys picta bellii. Skinned multicellular preparations were exposed to six treatments with physiologically relevant levels of pH (7.4, 7.0, 6.6), and Pi (3 mM and 8 mM). Each preparation was tested in a range of calcium concentrations (pCa 9.0-pCa 4.5) to determine the pCa-tension relationship for each treatment. Acidosis significantly decreased contractility by decreasing Ca2+ sensitivity (pCa50) and tension development (p<0.001). Increasing [Pi] also decreased contractility by decreasing tension development at every pH level (p<0.001), but alone, did not affect Ca2+ sensitivity (P=0.689). Simultaneous increases in [H+] and [Pi] interacted to attenuate the decreased tension development and Ca2+ sensitivity (p<0.001), possibly reflecting a decreased sensitivity to Pi when it is present as the dihydrogen phosphate form, which increases as pH decreases. Compared to mammals, the ventricle of turtles exhibits higher Ca2+ sensitivity, which is consistent with previous studies of ectothermic vertebrates. [ABSTRACT FROM AUTHOR]