Temperature, vertebrates via delivery oxygen and nutrients to tissue

Temperature, the abiotic master
environmental factor, has a profound effect on the abundance and distribution
of animals on the earth. Ectothermic animals (fishes, frogs, reptiles, and
invertebrate animals), cannot physiologically regulate their body temperature,
and are therefore especially vulnerable to temperature changes to which they
are not adapted but to which they might be exposed on the warming earth.
Indeed, understanding how climate change will affect animal life is one of the
greatest challenges of the current biological research. Climate warming is
considered to be the most serious environmental threat, in particular for aquatic
ecosystems and their biodiversity. According to the current scenarios, the
annual mean temperature in Finland is projected to rise by 2-5°C and 2-7°C by
the 2050s and 2080s, respectively. The duration of ice cover in lakes will
become shorter, winters will be milder and extreme temperature peaks are likely
to be higher and occur more often which inturn will affect fish populations in
Finland. Predicted increases in ambient temperature will acts as a leading
factor which control the boundary of habitats, locomotion, reproduction,
development, immune defense and general performance level of fishes and other
ectotherms, and thereby will impact the distribution and abundance of animal
species and possibly distort the delicate balance of the ecosystems to which
they belong.

Fishes
represent the most variable and largest group among vertebrates. Acute and
chronic temperature changes will be reflected on the cardiac function which
considers as a key physiological variable in environmental adaptation and
acclimation of aquatic vertebrates via delivery oxygen and nutrients to tissue
cells and providing homeostatic balance between body parts. In northern
latitudes, All fishes have to tolerate large seasonal temperature changes:
their hearts have to function close to zero in winter, while summer
temperatures may be 20-30 degrees higher. Heart muscle is electrically
excitable, i.e. a small voltage change of plasma membrane (cardiac action
potential, AP) sets the rate and rhythm of the heart, initiates contraction and
regulates force production of cardiac myocytes. Cardiac AP is generated by a
delicate and complex interaction between several ion channels in the cell
membrane. Hence small disturbances in ion channel function may generate
arrhythmias, cause conduction failures and compromise force of cardiac
contraction. Moreover,  thermal
plasticity of fish heart is crucial to maintain contractility and to avoid
disturbances in electrical excitability that should be sensitive and stable to
temperature changes to produce temperature-dependent acceleration and
deceleration of heart rate (fH) and coordinate changes in
conduction rate of action potential (AP) over the heart. Strongly response of
fishes to the warming makes them as indicator for detecting and documenting
climate-induced modifications on aquatic ecosystems. To this end, effects of seasonal
acclimatzation on the electrical excitbility of roach (Rutilus rutilus) heart,
one of the most abundant fish species of Finnish lakes and coastal waters, is
examined. The hypothesis of temperature-dependent depression of electrical
excitation (TDEE) is recently suggested by Vornanen (2016), the mismatch between
the temperature-dependent of outward K+ and inward Na+
may cause compromise in the electrical excitability, is also examined in roach
cardiomyocytes. Responses of roach heart to temperature changes are determined
at different levels of biological organization starting from in vivo
recordings of heart function in living animals down to organ, cell and molecule
level of in vitro experiments.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

The present
study revealed that seasonal acclimatization of electrical excitation is crucial
for proper function of roach heart under widely range of water temperatures in
winter and summer seasons. Seasonal thermal acclimation of electrical
excitability increases pumping capacity of the roach heart by increasing fH
in both seasons to the maximum without compromising the stability of cardiac
excitation. Sensitivity to thermal disturbances increases with increasing
complexity of biological organization, molecular functions being generally the
intact organism the most temperature sensitive and the most temperature
resistant. The upper thermal tolerance of the heart rate (fH)
is higher in summer- than in winter-acclimatized roach. Cardiac arrhythmias
appeared with rising temperature around and above the break point temperature (TBP),
the temperature after which steady increase/decrease of the variables reversed
into continuous decrease/increase, as missing QRS complexes, increase in
variability of heart rate, episodes of atrial tachycardia, ventricular
bradycardia and complete cessation of contractility (asystole) in both seasonal
acclimatized groups. Interestingly, Action potential (AP) of atrial myocytes in
summer roach recorded by microelectrode technique were characterized by a fast
initial repolarization which appeared as shortening in atrial AP duration at
10% (APD10) and 20% (APD20) repolarization levels in
comparison to atrial myocytes of winter roach. Among ion currents, the inward
rectifier K+ current (IK1) has the highest thermal
tolerance, while sodium current (INa) is the lowest one in both
seasonal groups. in winter acclimatized roach, the lower thermal tolerance of INa
is consistent with the lower thermal tolerance of in vivo fH,
while the matching between INa and fH is not ideal
in summer- as winter-acclimatized roach, thus other factors beside INa
may be included. In both seasonal acclimatized groups, molecular composition of
ion channels regulates ion currents in temperature-dependend manner and
consistent with the electrophysiological data.

Exercise,
capture and handling stress can cause remarkable changes in metabolite and ion
composition of the extracellular fluid and elevate extracellular K+
concentration (K+o) which may result in significant
post-stress mortality of fishes. In the current study, The combined effects
high temperature and high extracellular potassium concentration K+o
on electrical excitability of winter-acclimatized roach ventricular myocytes was
examined. Surprisingly, some myocytes completely failed to elicit all-or-none
AP in 8 mM K+o at 24°C with reduction in AP amplitude
and overshoot by elevation of K+o. Effects of high K+o
antagonizes the negative effects of high temperature on excitation threshold,
the precipitous depression of the rate of AP upstroke and complete loss of
excitability in some myocytes suggest that the combination of high temperature
and high K+o will severely impair ventricular
excitability in roach.

Briefly, sodium
current (INa) is clearly the most heat-sensitive ionic current, and considering
the weakest link which probably limiting the upper thermal tolerance of
electrical excitation in roach cardiomyocytes. Our current findings are
consistent with the hypothesis of the TDEE in that a mismatch in temperature-dependence
between inward INa and outward IK1, is causative to high
temperature-induced arrhythmias and bradycardia in fish hearts in vivo.
Also, current findings may provide a mechanistic explanation for thermal
deterioration and post-exercise depression of the heart rate, and therefore
poor survival of fishes exposed to thermal, exercise and handling stresses.

x

Hi!
I'm Dominick!

Would you like to get a custom essay? How about receiving a customized one?

Check it out
x

Hi!
I'm Dominick!

Would you like to get a custom essay? How about receiving a customized one?

Check it out