Electrical and mechanical effects induced by cold temperatures in the ventricle of isolated Rana ridibunda hearts

A temperature decrease changes the contractility of the amphibian heart, but the underlying mechanisms are not totally understood. The objectives of the present work were to better understand the intrinsic mechanisms supporting contractility changes induced by a rapid temperature decrease in the ventricle of Rana ridibunda, and to investigate how fast they develop. Ventricular mechanical cycles (VMCs) and monophasic action potentials (MAPs) recorded from 15 isolated hearts were measured at 15, 30, 45, 60, 90, 120 and 150 s after the application of Ringer solutions of 20, 10 and 5 degrees C. Treatment with 10 and 5 degrees C Ringer solutions decreased the heart rate, and increased the magnitude of the ventricular contraction and the duration of the contraction and relaxation periods. The electrical changes included prolongation of the MAP depolarization plateau, which also decreased in amplitude as an effect of perfusion with 5 degrees C Ringer solution. In addition, treatment with 5 degrees C Ringer solution increased the latency of contraction. The block of L-type channels totally abolished the depolarization plateau at all perfusion temperatures, but failed to inhibit ventricular contraction. In conclusion, treatment with cold temperatures changes the electrical activity of the ventricular myocardium in R. ridibunda hearts, which results in modified ventricular contractility. Data suggest that in addition to L-type Ca2+ channels, other components that support calcium elevation are present R. ridibunda ventricular cells.     

Electrical and mechanical activity of isoproterenol-damaged frog heart

The electrical and mechanical activities of myocardial strips from Rana pipiens were studied in the steady state at various stimulation frequencies and after a period of rest. The temperature of the bath was varied between + 12 and 35 degrees C. Normal myocardium was compared with that damaged by isoproterenol (ISO). The percentage change of action potential durations (APD50) and isometric force (P) was similar in ISO-damaged and control hearts at various bath temperatures with steady state stimulation rates between 20 and 100/min. At low stimulation rates (3-6/min) the prolongation of the action potential (AP) was more pronounced and the P-decrease was less in ISO-damaged myocardium compared to controls. These differences became more apparent at low bath temperatures. After 10 min of rest, APD50-90 was significantly prolonged in ISO-damaged heart and P was increased by a factor of 2 compared to controls (stimulation rate 20/min). Steady state values, on the other hand, were nearly the same in both groups. These findings are interpreted as indicating a temperature or ISO-dependent increase of electrogenic trans-sarcolemmal Ca2+-uptake during low frequency, or post-rest stimulation, either directly by an increase of the slow inward current (Isi), or indirectly by decreased K+-permeabilities.     

Temperature-dependent inotropic action of A23187 on guinea-pig ventricular muscles

The effects of the Ca2+ ionophore, A23187, on the contraction and membrane action potential of the isolated guinea-pig papillary muscle were examined at various temperatures (30-16 degrees C) and compared to those of isoprenaline and a high calcium medium. A23187 caused a marked positive inotropic effect with a significant prolongation of the action potential duration at an early repolarization phase but not a late repolarization phase at normal temperature (30 degrees C). Such an inotropic effect was completely abolished at low temperature (16 degrees C) where a marked positive inotropic effect of isoprenaline (5 X 10(-8) M) and a high calcium medium (6.2 mM) still remained. These results suggest that the cardiac responsiveness to A23187 was sensitive to a low temperature at which a membrane lipid phase transition may occur.     

The effect of acclimation temperature on the fusion kinetics of lipid vesicles derived from endoplasmic reticulum membranes of rainbow trout (Oncorhynchus mykiss) liver

Membrane fusion is an obligatory step in many vital cellular processes. The well-established enrichment of bilayer-destabilizing lipids in membranes of poikilotherms subjected to growth at low temperatures leads to the prediction that such membranes will possess a greater propensity to undergo fusion. This hypothesis was explicitly tested in the present study by determining the kinetics of fusion between small unilamellar vesicles (SUVs) prepared from endoplasmic reticulum (ER) membranes of thermally-acclimated (to 5 and 20 degrees C) rainbow trout (Oncorhynchus mykiss) liver and bovine brain phosphatidylserine (BBPS). At temperatures above 10 degrees C, ER vesicles from 5 degrees C-acclimated trout, fused more rapidly and to a greater extent with BBPS vesicles (by average factors of 1.25- and 1.45-fold, respectively) than ER vesicles of 20 degrees C-acclimated trout. At temperatures >35 degrees C, apparent fusion rates declined while the extent of fusion increased in both acclimation groups. Fusion kinetics were found to be well correlated with and limited by the physical properties and phase state of the BBPS vesicles. These results indicate that dynamic attributes of biological membranes, such as the propensity to undergo fusion, are of potential regulatory significance and are partially conserved when growth or environmental temperature changes.     

Temperature effects on the Na and Ca currents in rat and hedgehog ventricular muscle

Cardiac transmembrane potentials and Na and Ca currents were recorded at different temperatures in rat and hedgehog ventricular muscle. At 35 degrees C in both species resting potential was about -80 mV and upstroke velocity (Vmax) of the action potential above 100 V/s. The shape of the action potential in hedgehog ventricular cells at 35 degrees C was similar to that in the rat showing a fast repolarization phase. When temperature was decreased, the membrane resting potential depolarized and action potential amplitude and Vmax declined. In rat ventricular cells at 10 degrees C, the resting potential was about -40 to -50 mV and Vmax was reduced to about 5 V/s. In hedgehog ventricular cells, however, the transmembrane potentials and Vmax were better maintained at low temperature. Phase 3 of the action potential was markedly prolonged below 20 degrees C in hedgehog but not in rat ventricular cells. When temperature was decreased to 10 degrees C the availability curve of the Na current shifted toward more negative potentials and ICa.peak declined in rat ventricular cells. In hedgehog cardiac preparations, the Na current was less influenced by the cooling and ICa.peak did not change very much at low temperatures. A transient inward current usually considered to induce cardiac arrhythmias could be recorded in rat ventricular cells below 20 degrees C but not in hedgehog preparations. These features of hedgehog cardiac membranes may contribute to the cold tolerance and the resistance to ventricular fibrillation during the hypothermia in mammalian hibernators.     

Properties of HERG channels stably expressed in HEK 293 cells studied at physiological temperature.

We have established stably transfected HEK 293 cell lines expressing high levels of functional human ether-a go-go-related gene (HERG) channels. We used these cells to study biochemical characteristics of HERG protein, and to study electrophysiological and pharmacological properties of HERG channel current at 35 degrees C. HERG-transfected cells expressed an mRNA band at 4.0 kb. Western blot analysis showed two protein bands (155 and 135 kDa) slightly larger than the predicted molecular mass (127 kDa). Treatment with N-glycosidase F converted both bands to smaller molecular mass, suggesting that both are glycosylated, but at different levels. HERG current activated at voltages positive to -50 mV, maximum current was reached with depolarizing steps to -10 mV, and the current amplitude declined at more positive voltages, similar to HERG channel current expressed in other heterologous systems. Current density at 35 degrees C, compared with 23 degrees C, was increased by more than twofold to a maximum of 53.4 +/- 6.5 pA/pF. Activation, inactivation, recovery from inactivation, and deactivation kinetics were rapid at 35 degrees C, and more closely resemble values reported for the rapidly activating delayed rectifier K+ current (I(Kr)) at physiological temperatures. HERG channels were highly selective for K+. When we used an action potential clamp technique, HERG current activation began shortly after the upstroke of the action potential waveform. HERG current increased during repolarization to reach a maximum amplitude during phases 2 and 3 of the cardiac action potential. HERG contributed current throughout the return of the membrane to the resting potential, and deactivation of HERG current could participate in phase 4 depolarization. HERG current was blocked by low concentrations of E-4031 (IC50 7.7 nM), a value close to that reported for I(Kr) in native cardiac myocytes. Our data support the postulate that HERG encodes a major constituent of I(Kr) and suggest that at physiological temperatures HERG contributes current throughout most of the action potential and into the postrepolarization period.     

Rapid cold hardening in the predatory mite Euseius (Amblyseius) finlandicus (Acari: Phytoseiidae)

A rapid cold hardening response was studied in diapause and non-diapause females of the predatory mite Euseius finlandicus. When laboratory reared diapause and non-diapause females were transferred and maintained from the rearing temperature of 20 degrees C for 2 h to -11.5 degrees C and -10 degrees C, 10 to 20% survived respectively. However, conditioning of diapause females for 4 h at a range of temperatures from 0 to 10 degrees C before their exposure for 2 h to -11.5 degrees C, increased survival to approximately 90%. Similarly, conditioning of non-diapause females for 4 h at 5 degrees C before their exposure for 2 h to -10 degrees C increased survival to 90%. A similar rapid cold hardening response in both diapause and non-diapause females was also induced through gradual cooling of the mites, at a rate of approximately 0.4 degrees C per min. The rapid increase in cold tolerance after prior conditioning of the mites to low temperatures, was rapidly lost when they returned to a higher temperature of 20 degrees C. Rapid cold hardening extended the survival time of diapause and non-diapause females at sub-zero temperatures. The cost of rapid cold hardening in reproductive potential after diapause termination was negligible. In non-diapause females, however, the increase in cold tolerance gained through gradual cooling could not prevent cold shock injuries, as both fecundity and survival were reduced.     

Transition temperatures of the electrical activity of ion channels in the nerve membrane

The temperature dependence of some of the electrical characteristics of neuronal membranes from Aplysia giant neurons and crustacean and cuttlefish giant axons has been analyzed. Arrhenius plots for the maximum rate of depolarization of (V+max) or repolarization (V-max) of the action potential, for the resting membrane conductance, and for the speed of propagation of the action potential, exhibited clear breaks at characteristic temperatures between 17 and 20 degrees C. Lobster giant axons and frog nodes of Ranvier were voltage-clamped at different temperatures between 5 and 30 degrees C. Arrhenius plots for relaxation times related to the opening and closing processes affecting the Na+ and K+ channels were linear. No 'transition' temperature was detected. However, clear-cut changes in (Formula: see text) Na+ and K+ currents, were consistantly observed around 18 degrees C. Values for (Formula: see text) plateaued above 18 degrees C, then decreased gradually as a function of reduced temperature. Variations in temperature between 1 and 30 degrees C did not alter the binding properties of [3H]tetrodotoxin to a purified crab axonal membrane. Pharmacological properties of the Na+ channel are sensitive to temperature. The temperature-dependent effect of veratridine has been studied and indicates a change in properties of the Na+ channel below 20 degrees C. These results support the possibility that the fluidity of membrane lipids in the ionic channel microenvironment may influence the degree to which the channel can open.     

Effects of temperature and calcium availability on ventricular myocardium from rainbow trout

We studied the mechanical and electrophysiological properties of ventricular myocardium from rainbow trout (Oncorhynchus mykiss) in vitro at 4, 10, and 18 degrees C from fish acclimated at 10 degrees C. Temperature alone did not significantly alter the contractile force of the myocardium, but the time to peak tension and time to 80% relaxation were prolonged at 4 degrees C and shortened at 18 degrees C. The duration of the action potential was also prolonged at 4 degrees C and progressively shortened at higher temperatures. An alteration of the stimulation frequency did not affect contraction amplitude at any temperature. Calcium influx via L-type calcium channels was increased by raising extracellular calcium concentration (?Ca(2+)(o)) or including Bay K 8644 (Bay K) and isoproterenol in the bathing medium. These treatments significantly enhanced the contractile force at all temperatures. Calcium channel blockers had a reverse-negative inotropic effect. Unexpectedly, the duration of the action potential at 10 degrees C was shortened as ?Ca(2+)(o) increased. However, Bay K prolonged the plateau phase at 4 degrees C. Caffeine, which promotes the release of sarcoplasmic reticulum (SR) calcium, increased contractile force eightfold at all three temperatures, but the SR blocker ryanodine was only inhibitory at 4 degrees C. Our results suggest that contractile force in ventricular myocardium from Oncorhynchus mykiss is primarily regulated by sarcolemmal calcium influx and that ventricular contractility is maintained during exposure to a wide range of temperatures.     

Kinetics and in vitro origin of the temperature-dependent transition of the estrogen receptor monomer

Partitioning of estrogen receptors in aqueous two-phase polymer systems has provided the basis for a detailed kinetic analysis of the effects of temperature on estrogen receptor (ER) structure in vitro. Exposure to temperatures of 0-30 degrees C increased the rate of change in ER partition coefficients by up to 100-fold but did not affect the final extent of the process. The temperature-dependent change in ER partition coefficients was characterized by a linear Arrhenius plot and an activation energy of 25 kcal/mol. The rate of the temperature-dependent ER transition (28 degrees C) was found to be unaffected by greater than 50-fold changes in receptor concentration, which indicates that the temperature-dependent change in partition coefficients reflects a first-order process. The partition coefficients of heated ER were unaffected by subsequent 18-h incubations at 0 degree C, indicating that the temperature-dependent ER transition is irreversible in vitro. Direct heating of the unoccupied ER resulted in both a change in ER partition coefficients and a loss of ER binding sites. The temperature-dependent change in unoccupied ER partition coefficients was complete within 30 min at 28 degrees C and yielded a first-order rate constant that was the same as that obtained for heating the receptor-estradiol complex at 28 degrees C. In contrast, the loss of unoccupied ER binding sites that occurred during 28 degrees C incubations did not reach completion after 150 min of heating and was found to behave as a second-order process.(ABSTRACT TRUNCATED AT 250 WORDS)     

Is glutamate the transmitter of crustacean motoneurons?

1. Bath-application of L-glutamate to crayfish opener muscle causes depolarization and resistance changes which both increase with falling temperature. At temperatures above 15 degrees C there is usually a resistance increase, at lower temperatures the resistance is decreased. 2. Meso-gamma . gamma'-diaminosuberic acid-dihydrochloride (meso-di-GABA) and dl-diamino-nonanedicarboxylic acid dihydrochloride (C-9) were newly synthesized as potential glutamate blockers. 3. Meso-di-GABA (10(-4) to 10(-3)M) usually caused a significant increase (15 degrees C) or decrease (7 degrees C) of membrane resistance and slight depolarization. Excitatory junction potentials (ejps) were reversibly depressed or blocked while the effects of glutamate were potentiated. The depression or block of neuromuscular transmission was not prevented by picrotoxin or by concanavaline A. 4. C-9 (3 x 10(-4) M) depressed or blocked the effect of applied glutamate with little or no effect on ejps. 5. The results are best explained by assuming that bath-applied glutamate acts mainly on extrasynaptic receptors. Meso-di-GABA is assumed to block synaptic receptors and to activate non-synaptic receptors while C-9 seems to act mainly as a blocker of glutamate action on non-synaptic receptors.     

The potential fertility estimation capacity of the hypoosmotic swelling test, the thermal stress test and a modified cervical mucus penetration test in the bovine

In this study, hypoosmotic swelling (HOS), thermal stress (TS) and modified cervical mucus penetration (mCMP) tests have been used with routine tests for the assessment of semen quality. This is the first study in which the comparison of potential fertility estimation of fore-mention three tests was performed. Bull semen samples were divided into two fertility groups (high: n=3, low: n=3), according to their post-insemination NRR (non-return rate). Prior to the tests, post-thawed spermatological characteristics were assessed after which HOS, TS and mCMP tests were carried out. In the HOS test, the ratio of swollen cells, in the TS test the motility, and in the mCMP test the number of spermatozoa penetrating the cervical mucus, were examined. The relationship between the tests and fertility was also evaluated. HOS test was carried out according to different incubation times and temperatures (37 degrees C 60 min/41 degrees C 15 min/41 degrees C 30 min/46 degrees C 15 min/46 degrees C 30 min). For TS test, samples were subjected to various temperatures for different periods (no incubation (37 degrees C)/41 degrees C 15 min/41 degrees C 30 min/46 degrees C 15 min/46 degrees C 30 min). The mCMP test were subjected to various temperatures for the same period (37 degrees C 15 min/41 degrees C 15 min). In this study, post-thawed motility was found to be similar in high and low fertility groups. However, it has been determined that acrosomal (p<0.01) and other morphological defects (p<0.05) were low in the high fertility group. When HOS test was carried out at 37 degrees C, no difference was observed between the bulls with high and low fertility, but at 41 and 46 degrees C, results of high fertility group were significantly higher than those of low fertility group (p<0.01). Similarly in TS test, the progressive motility rates of high fertility bulls was higher after thermal practices at 41 and 46 degrees C (p<0.01). In mCMP test, at 37 degrees C, the number of cells that had penetrated was similar. However, significant differences were observed in the incubation at 41 degrees C (p<0.01). It has been concluded that for the estimation of potential fertility of bulls, HOS, TS and mCMP tests, in combination with routine spermatological tests can be used and the use of further penetration distance range (PDR2) in mCMP test and higher temperatures such as 41 degrees C instead of 37 degrees C, during the incubations in the afore-mentioned performance tests, is more determinative.     

The action of ultrasound on the contraction strength and action potential of the papillary muscle of the rat heart

In experiments on isolated rat papillary muscles the effects of therapeutic doses of ultrasound (US) (intensity, less than 2 W/cm2) with frequency of 0.88 MHz on contraction force and action potential (AP) were studied. 12 muscles (from 14) responded to 3-min exposition of the US with a rise both in contraction force and in resting tension. Sensitivity to US and a value of inotropic effect changed significantly between the preparation, and the threshold intensities of US varied from 0.3 to 2 W/cm2. In 3 experiments the inotropic effect of US was more than 100%, but in others it was about 50%. Two preparations were not sensitive to the US. The positive inotropic effect of US was accompanied by membrane depolarization (up to 20 mV) and by prolongation of AP duration measured at 10% of its amplitude (APD10). The correlation between the increase in contraction force and APD10 was demonstrated. Some preparations responded to US with high depolarization (up to 50 mV) and were inexcitable. The US induced an increase in temperature less than 1 degree C, therefore all the effects of US could not be explained as a result of temperature rise.     

Calcium transport in diluted or cooled ram semen

Ram semen was subjected to various dilution rates and temperatures of dilution, and was also subjected to slow cooling and rewarming. Calcium ion movements across sperm membranes were measured using the radioisotope 45Ca2+. It was shown that even 2- to 4-fold dilution caused an increase in intracellular calcium content. An increase in intracellular calcium also occurred in proportion to a decreased temperature of dilution. After an initial increase in intracellular calcium content, spermatozoa appeared able to restore a low intracellular calcium level over a period of 2 h at 22 degrees C or above. This ability was lost at 16 degrees C or below. However, if undiluted semen was slowly cooled (0.125 degrees C/min) even to 5 degrees C and rewarmed to 22 degrees C before dilution, the spermatozoa regained this ability. In contrast, spermatozoa rapidly cooled to 5 degrees C and rewarmed to 22 degrees C before dilution were not able to restore the low intracellular calcium level.     

The effects of low temperatures on intracellular transport of newly synthesized albumin and haptoglobin in rat hepatocytes.

Isolated rat hepatocytes were pulse-labelled with [35S]methionine at 37 degrees C and subsequently incubated (chased) for different periods of time at different temperatures (37-16 degrees C). The time courses for the secretion of [35S]methionine-labelled albumin and haptoglobin were determined by quantitative immunoprecipitation of the detergent-solubilized cells and of the chase media. Both proteins appeared in the chase medium only after a lag period, the length of which increased markedly with decreasing chase temperature: from about 10 and 20 min at 37 degrees C to about 60 and 120 min at 20 degrees C for albumin and haptoglobin respectively. The rates at which the proteins were externalized after the lag period were also strongly affected by temperature, the half-time for secretion being 20 min at 37 degrees C and 200 min at 20 degrees C for albumin; at 16 degrees C no secretion could be detected after incubation for 270 min. Analysis by subcellular fractionation showed that part of the lag occurred in the endoplasmic reticulum and that the rate of transfer to the Golgi complex was very temperature-dependent. The maximum amount of the two pulse-labelled proteins in Golgi fractions prepared from cells after different times of chase decreased with decreasing incubation temperatures, indicating that the transport from the Golgi complex to the cell surface was less affected by low temperatures than was the transport from the endoplasmic reticulum to the Golgi complex.     

Brefeldin A redistributes resident and itinerant Golgi proteins to the endoplasmic reticulum

Brefeldin A (BFA) has been reported to block protein transport from the ER and cause disassembly of the Golgi complex. We have examined the effects of BFA on the transport and processing of the vesicular stomatitis virus G protein, a model integral membrane protein. Delivery of G protein to the cell surface was reversibly blocked by 6 micrograms/ml BFA. Pulse-label experiments revealed that in the presence of BFA, G protein became completely resistant to endoglycosidase H digestion. Addition of sialic acid, a trans-Golgi event, was not observed. Despite processing by cis- and medial Golgi enzymes, G protein was localized by indirect immunofluorescence to a reticular distribution characteristic of the ER. By preventing transport of G protein from the ER with the metabolic inhibitor carbonyl cyanide m-chlorophenylhydrazone or by use of the temperature-sensitive mutant ts045, which is restricted to the ER at 40 degrees C, we showed that processing of G protein occurred in the ER and was not due to retention of newly synthesized Golgi enzymes. Rather, redistribution of preexisting cis and medial Golgi enzymes to the ER occurred as soon as 2.5 min after addition of BFA, and was complete by 10-15 min. Delivery of Golgi enzymes to the ER was energy dependent and occurred only at temperatures greater than or equal to 20 degrees C. BFA also induced retrograde transport of G protein from the medial Golgi to the ER. Golgi enzymes were completely recovered from the ER 10 min after removal of BFA. These findings demonstrate that BFA induces retrograde transport of both resident and itinerant Golgi proteins to the ER in a fully reversible manner.     

The effect of thawing velocity on survival and acrosomal integrity of ram spermatozoa frozen at optimal and suboptimal rates in straws

The effect of various thawing velocities on the motility and acrosomal maintenance of ram spermatozoa frozen at 20 degrees C/min (optimal) or 2 degrees C/min (suboptimal) was studied. The freeze-thaw motility and the percentage of intact acrosomes of spermatozoa frozen at 20 degrees C/min increased progressively with the thawing velocity. In semen frozen at 2 degrees C/min, motility of spermatozoa and the percentage of intact acrosomes declined drastically when the thawing velocity obtained in air at 20 degrees C was increased by thawing in water at 20 degrees C. Thawing at higher temperatures markedly increased both motility and acrosomal preservation, but the best results with semen frozen at 2 degrees C/min were lower than those obtained with semen frozen at 20 degrees C/min. The optimal freeze-thaw conditions for semen protected by 4% glycerol were freezing at 20 degrees C/min and thawing in water at 60 or 80 degrees C for 8 or 5 sec, respectively. Semen collected from rams exposed to a decreasing photoperiod exhibited higher motility after freezing and thawing than those exposed to an increasing photoperiod. However, there was no effect on acrosomal preservation after freezing at 20 degrees C/min.     

Temperature dependence of mammalian muscle contractions and ATPase activities

Isolated rat and mouse extensor digitorum longus (EDL) and soleus muscles were studied under isometric and isotonic conditions at temperatures from approximately 8 degrees -38 degrees C. The rate constant for the exponential rise of tension during an isometric tetanus had a Q10 of approximately 2.5 for all muscles (corresponding to an enthalpy of activation, delta H = 66 kJ/mol, if the rate was determined by a single chemical reaction). The half-contraction time, contraction time, and maximum rate of rise for tension in an isometric twitch and the maximum shortening velocity in an isotonic contraction all had a similar temperature dependence (i.e., delta H approximately 66 kJ/mol). The Mg++ ATPase rates of myofibrils prepared from rat EDL and soleus muscles had a steeper temperature dependence (delta H = 130 kJ/mol), but absolute rates at 20 degrees C were lower than the rate of rise of tension. This suggests that the Mg++ ATPase cycle rate is not limiting for force generation. A substantial fraction of cross-bridges may exist in a resting state that converts to the force-producing state at a rate faster than required to complete the cycle and repopulate the resting state. The temperature dependence for the rate constant of the exponential decay of tension during an isometric twitch or short tetanus (and the half-fall time of a twitch) had a break point at approximately 20 degrees C, with apparent enthalpy values of delta H = 117 kJ/mol below 20 degrees C and delta H = 70 kJ/mol above 20 degrees C. The break point and the values of delta H at high and low temperatures agree closely with published values for the delta H of the sarcoplasmic reticulum (SR) Ca++ ATPase. Thus, the temperature dependence for the relaxation rate of a twitch or a short tetanus is consistent with that for the reabsorption rate of Ca++ into the SR.     

Survival of indianmeal moth and navel orangeworm (Lepidoptera: Pyralidae) at low temperatures

Concerns over insect resistance, regulatory action, and the needs of organic processors have generated renewed interest in developing nonchemical alternative postharvest treatments to fumigants used on dried fruits and nuts. Low-temperature storage has been identified as one alternative for the Indianmeal moth, Plodia interpunctella (Hiibner), and navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), common postharvest pests in California dried fruits and nuts. The response of eggs, nondiapausing larvae, and pupae of both species to exposure to low temperatures (0, 5, and 10 degrees C) was evaluated. Eggs of both species were the least tolerant of low temperatures. At 0 and 5 degrees C, pupae were most tolerant, but at 10 degrees C, nondiapausing larvae of both species were most tolerant, with lethal time (LT)95 values of 127 and 100 d for Indianmeal moth and navel orangeworm, respectively. The response of diapausing Indianmeal moth larvae to subfreezing temperatures also was evaluated. Diapausing larvae were very cold tolerant at -10 degrees C, with LT95 values of 20 and 17 d for long-term laboratory and recently isolated cultures, respectively. Diapausing larvae were far less tolerant at lower temperatures. At -15 degrees C, LT95 values for both cultures were <23 h, and at -20 degrees C, LT95 values were <7 h. Refrigeration temperatures of 0-5 degrees C should be useful in disinfesting product contaminated with nondiapausing insects, with storage times of 3 wk needed for adequate control. Relatively brief storage in commercial freezers, provided that the temperature throughout the product was below -15 degrees C for at least 48 h, also shows potential as a disinfestation treatment, and it is necessary when diapausing Indianmeal moth larvae are present.     

Flight muscle resting potential and species-specific differences in chill-coma

Resting potentials in Apis mellifera and Drosophila melanogaster flight muscles decrease with falling temperatures. When resting potentials fall to between -37 and -45 mV they activate a final burst of spontaneous muscle action potentials (MAPs). This final burst of MAPs marks the beginning of chill-coma for each species. The temperature at which the final burst occurs for D. melanogaster (7.0+/-0.9 degrees C) is significantly lower than that of A. mellifera workers (10.6+/-1.2 degrees C), queens (10.2+/-0.8 degrees C), and drones (12.8+/-0.8 degrees C). Prior to chill-coma, MAP amplitudes decrease and durations increase with falling temperatures in both A. mellifera and D. melanogaster. The rate of these changes and the temperatures at which they occur appear to be related to the rate of decline in each species' resting potential. These results suggest that insect chill-coma varies with a species' ability to maintain its resting potential at low temperatures.