Hsp levels in toad heart are independent of temperature and pharmacological stimuli

Abstract

Expression of Hsp70 in heart and skeletal muscle in two species of toads (Bufo viridis and B. regularis) that reside in different climatic regions and differ profoundly in their temperature sensitivity was studied at room temperature and upon various acclimation conditions. The effects of hypoxia, phenylephrine and clonidine on heart rate, ECG and Hsp70 expression were also investigated. High and variable levels of Hsp70 were detected in heart tissue of both species, compared with Hsp70 levels detected in skeletal muscle. Although there seems to be somewhat higher expression in B. regularis heart, low temperature did not influence the Hsp70 level appreciably and did not differ much from the control. Expression of HSF1 in heart extract of B. viridis and Xenopus laevis in relation to various thermal procedures falls within the same range, and if at all, it was reduced by the thermal treatments. HSF1-HSE binding occurred randomly in the two species, and was unrelated to the thermal treatments. Specific HSF1-HSE binding occurred only when thermal treatment was combined with phenylephrine injection. Hsp70 expression was highest at control conditions, unrelated to HSF1-HSE binding, and remained almost unchanged after phenylephrine injections and cold shock. Heart rate was greatly reduced and QRS amplitude was diminished in response to both hypoxia and clonidine injection. Hsp70 expression, on the other hand, was maximal in hypoxic tissue at room temperature, and was paralleled by a modest binding of HSF1 to HSE. In all other conditions, the prominent radioactive complex was unrelated to the expression of Hsp70. Hsp level both in the heart and skeletal muscle do not seem then to be directly involved in the response to thermal changes and pharmacological stimuli. The results are discussed in the framework of a strategy, frequent among poikilotherms, that involves maintenance of a high resting level of Hsp.

THERMAL STRESS INDUCES HSP70 PROTEINS SYNTHESIS IN LARVAE OF THE COLD STREAM NON‐BITING MIDGE Diamesa cinerellaMeigen

“…Due to the commercial antibody we used, cross-reacting with several HSP70 family members, the HSP70 levels we found may be a reflection of inducible, constitutive, or both forms of HSPs (HSP/HSC). Notwithstanding, in terms of the total amount of HSPs, intraspecies comparisons preserve their validity as suggested by other authors using the same type of antibody (Airaksinen et al, 2003;Chapovetsky and Katz, 2006).…”

“…The strategy of expressing hsp genes continuously is adopted by other several organisms belonging to animals and protists living in very cold environments of polar and temperate zones to avoid protein denaturation due to low temperatures (Joplin et al, 1990;Yocum et al, 1991;Denlinger et al, 1992;Lee et al, 1995;Feder and Hofmann, 1999;Carpenter and Hofmann, 2000;La Terza et al, 2001;Place and Hofmann, 2005). According to Chapovetsky and Katz (2006), the presence of constitutively high levels of HSPs confers the capacity to respond promptly to any variation of environmental conditions. Zhang et al (2011) showed a consistent increase (1.5-to 2.0-fold) of HSP70 and other constitutive HSPs in the freeze-tolerant gall fly larvae of Eurosta solidaginis Fitch, 1855 (Diptera, Tephritidae) over late autumn-winter when they enter diapausa than in other periods of the year.…”

Expression of the 70 kDa Heat shock protein family in Alpine freshwater chironomids (Diptera, Chironomidae) under natural conditions

“…Due to the commercial antibody we used, cross-reacting with several Hsp70 family members, the Hsp70 levels we found may be a reflection of inducible, constitutive or both forms of heat shock proteins (Hsp/Hsc). Notwithstanding, in terms of total amount of heat shock proteins, intra-and inter-species comparisons preserve their validity as suggested by other authors using the same type of antibody (Airaksinen et al 2003;Chapovetsky & Katz 2006).…”

Each to their own: skeletal muscles of different function use different biochemical strategies during aestivation at high temperature

“…Constitutive expression of Hsp70 may protect against expected accumulation of oxidative stress over prolonged aestivation and against the oxidative insult upon arousal, and presumably further helps C. alboguttata to 'absorb' temperature fluctuations during aestivation. Constitutive expression of HSPs are a strategy common to amphibians (Chapovetsky and Katz, 2006) regardless of varying physiological tolerance to environmental stressors, and may be a strategy common to animals that undergo dormancy (Carey et al, 1999;Storey and Storey, 2011). Other HSPs with well-defined roles in muscle morphology and function such as Hsp27 (Folkesson et al, 2008;Sharp et al, 2006) and Hsc70 (heat shock cognate 70) via interactions with thiols (Hoppe et al, 2004) are also likely to be involved.…”