Operative environmental temperatures (Te, an index of the thermal environment) were measured for basking Pseudemys scripta in South Carolina. Operative environmental temperatures were good predictors of the basking behavior of P. scripta. Turtles in this study generally did not bask unless Te was 28°C (preferred body temperature) or higher. This demonstrated that basking was not a random behavior in respect to Te, and implicated thermoregulation as a major factor eliciting basking behavior. Operative environmental temperature was positively related to short—wave and total solar radition as well as to air and substrate temperature. Substrate temperature was the best single predictor of Te. A multiple regression equation (Te = 0.005R + 0.103Ta — 1.16 log V + 0.932Ts — 2.54, r2 = .90, where R = total radiation in watts per square metre, Ta = air temperature in degrees Celsius, V = wind speed in metres per second, and Ts = substrate temperature in degrees Celsius) defines the relationship of Te to microclimate variables. Movement of the sun through the day results in spatial variation in Te's available to turtles and influences their location and basking behavior.

Water, bottom, and presumed hibernaculum temperatures and dissolved oxygen concentrations were examined over four winter seasons (1981–1985) in a shallow pond near Ann Arbor, Michigan, where a population of painted turtles, Chrysemys picta, overwinter. The minimum presumed hibernaculum temperature varied considerably from year to year (3.7–6.3 °C) and was correlated with the severity of the winter. Turtles hibernating at this site would not have been exposed to temperatures below freezing even in the severest winter. Ice covered the pond continuously for an average of 92 (56–117) days and subsequently, dissolved oxygen fell precipitously, the water becoming severely hypoxic (< 1 ppm O2) for an average of 43 (39–46) days. The timing of emergence varied annually (March 1 to April 14) and was correlated with the severity of the winter. Thus, it appears that photoperiod or a circannual rhythm is not a proximate cue for arousal. Emergence generally occurred after the ice cover was completely melted, when water and bottom temperatures were increasing steadily and the vertical temperature gradient had collapsed or reversed. The annual variability in physical conditions demonstrated in this study strongly suggests that studies involving hibernation in aquatic ecosystems are best conducted over several winters.

Osmotic stress elicits hypertonic NaCl secretion and promotes structural and biochemical differentiation in avian salt glands. In addition to cholinergic control, Cl- secretion is stimulated by vasoactive intestinal peptide (VIP), suggesting that the cystic fibrosis transmembrane conductance regulator (CFTR) may be present and that its expression may be regulated by chronic salt stress. Anion efflux, assayed by 6-methoxy-N-(3-sulfopropyl)quinolinium fluorescence changes in single cells, was stimulated by VIP or 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate. Immunoblots with a COOH-terminal peptide antibody to human CFTR revealed approximately 170- and approximately 180-kDa bands in lysates from control and salt-stressed glands, respectively. Both variants reduced to approximately 140 kDa after N-glycanase digestion and gave identical tryptic phosphopeptide maps after immunoprecipitation and phosphorylation by protein kinase A. CFTR was localized to apical membranes by immunofluorescence and, additionally, to subapical vesicles by immunoelectron microscopy. Salt stress induced an approximately twofold increase in CFTR abundance/cell protein (approximately 5-fold/cell) and intensified apical membrane immunofluorescence. For comparison, Na+ pump expression increased approximately fourfold per cell protein with little change in actin. Thus differentiation induced by salt stress is accompanied by alteration in CFTR abundance and glycosylation. Upregulation of CFTR likely contributes to increased efficiency of Cl- secretion.

The amounts of energy liberating substrates in muscle, heart, liver and total carcass were determined in painted turtles just prior to (early October) and upon arousal from (late March) hibernation. Between the fall and spring samples, total carcass neutral lipids, protein and glycogen were depleted 37.g%, 11.0% and 70.2%, respectively. Total carcass lactate increased 551% in post-hibernatory turtles suggesting an important role for anaerobic glycolysis in producing energy during periods of anoxia. Females used more energy than males; however, the pattern of substrate utilization was similar in both sexes with lipid, protein and glycogen providing 56%, 27% and 17% of the energy, respectively.

Oscillations in intracellular calcium concentration ([Ca2+]i) induced by the acetylcholine analogue carbachol (CCh) were characterized by microspectrofluorimetry of fura-2 in single secretory cells from the avian salt gland. The frequency of oscillations increased in graded fashion with [CCh] between 25 nM (2.7 +/- 0.6 min-1) and 250 nM (11.8 +/- 1.4 min-1), whereas the amplitude of the spikes was independent of [CCh]. An interperiod return to prestimulatory [Ca2+]i was generally seen only at very low (25 nM) CCh. Between 50 and 250 nM CCh, oscillations were associated with sustained elevated [Ca2+]i levels. The amplitude of the oscillatory spikes was found not to exceed that of initial spikes arising from prestimulatory [Ca2+]i, despite the dose-dependent [effective concentration at 50% (EC50) = 200 nM CCh] sustained rise in [Ca2+]i. At 1 microM CCh, oscillations gave way to a maximal sustained increase in [Ca2+]i. Reduction of [Ca2+]o to 1.5 microM during an oscillatory train or blockage of Ca2+ influx with Ni+ resulted in a reduction in sustained Ca2+i levels and in frequency, but not amplitude, of oscillations. A relationship between the sustained partial rise in [Ca2+]i derived from Ca2+ influx and the oscillatory frequency at a given [CCh] was further indicated by the lower frequency (P less than 0.01) of the early spikes in a train when interspike [Ca2+]i initially returned to near-basal levels. In some cells, oscillations were slow enough (less than 2 min-1) to resolve an interperiod of elevated baseline [Ca2+]i, showing that the latter can occur independent of the repetitive Ca2+ spikes. (ABSTRACT TRUNCATED AT 250 WORDS)