Rauno Tirri

Temperature dependence of the heart isolated from the cold or warm acclimated perch (Perca fluviatilis)

Abstract 1. 1. Temperature dependence of beating pearch atrium showed an acclimation effect on rate of Precht type 3. Arrhenius plots were non-linear being steepest below 10°C in both 5° and 18–20°C acclimated groups. 2. 2. Temperature dependence of oxygen consumption of non-beating heart also showed the acclimation effect, but the Arrhenius plots were linear over the whole temperature range, 2–25°C. 3. 3. Morphometric analysis showed that the fractional volume of cardiac cells occupied by sarcoplasmic reticulum was greater in cold as compared to warm acclimated fish. No such difference was found for mitochondria.

Inhibitory adrenergic control of heart rate of perch (Perca fluviatilis) in vitro

1. Adrenaline and noradrenaline, but not isoprenaline or phenylephrine, showed a negative chronotropic effect on the isolated perch heart. 2. This adrenergic effect was blocked by an alpha-adrenergic antagonist, phentolamine, but not by a beta-blocker, propranolol, suggesting the role of alpha receptors in this action. 3. When a ligature between the atrium and the ventricle was used, adrenaline inhibited the beating of the atrium but not of the ventricle. This suggests that the negative chronotropic effect occurred in the whole heart through an atrial pacemaker (sinus node). 4. The sensitivity of the heart to the adrenergic effect was temperature-dependent and greater at low test temperature. At 15 degrees C pD2 for noradrenaline was 6.45 +/- 0.20 and for adrenaline 6.33 +/- 0.20. At 24 degrees C the values were 5.44 +/- 0.12 and 5.67 +/- 0.15, respectively.

Effects of intraventricular brain injections of neurotransmitters on colonic temperature in morphine-tolerant rats.

Abstract The possible sensitivity changes caused by morphine tolerance in the postsynaptic receptors of putative neurotransmitters involved in the central thermoregulatory mechanisms were studied by intraventricular brain injections of 5-HT, NA, DA, ACh, physostigmine, pilocarpine and carbachol into 20-day old morphine-tolerant and control rats. Temperature acclimation effects were ruled out by keeping the animals in a thermoneutral environment (32°C) during the periods in which morphine would ordinarily have caused hypothermia at lower environmental temperatures. At 22–24°C, the hypothermia produced by ACh, physostigmine and both in combination was significantly greater in morphine-tolerant animals, while there were no significant differences between tolerant and control animals in the colonic temperature responses to the other substances tested. It is suggested that cholinergic receptors of pronounced ACh specificity are induced in the central thermoregulatory neurones of immature rats by repeated administration of morphine for 6 days.

Isolation and characterization of single myocardial cells from the perch, Perca fluviatilis

In applying the enzymatic cell isolation technique to the fish heart about 40% of the dispersed myocytes maintained their spindle-shaped morphology, and about half of them tolerated physiological concentration of Ca2+ and excluded the vital dye, Evans blue. The length of spindle-shaped myocytes was on average 133 +/- 3 micron and the maximum width was 4.2 +/- 0.1 micron. The mean length of the sarcomeres was 2.1 +/- 0.1 micron. The sizes of the myocytes did not vary significantly with the weights of the fish. Electron microscopic examinations showed typical fish myocardial cell structure; absence of transverse tubule system, a sparse network of sarcoplasmic reticulum and from a few up to eight or more myofibrils. The cells were mononuclear. Most of the Ca2+-tolerant myocytes were quiescent, but the contraction in them could be induced by electric field stimulation. Both the spontaneous and electrically triggered contractions were of twitch type. The slowly propagating contraction waves, so-called phasic contractions common in isolated mammalian cardiac myocytes, could not be seen at all.

Alpha and beta adrenergic control of contraction force of perch heart perca fluviatilis in vitro

Noradrenaline showed a negative inotropic effect on the isolated electrically triggered atrium of the perch. The effect was stronger at lower temperature and was antagonized by an alpha adrenergic blocker, phentolamine. The inotropic effect of adrenaline was dependent on incubation temperature. The effect was negative at 15 C but biphasic at 24 C, where with increasing adrenaline concentration a positive inotropic effect was followed by negative inotropy. Phentolamine not only antagonized the negative inotropic effect of adrenaline at 15 degrees C but changed it to positive. This positive inotropic effect was antagonized by a beta adrenergic blocker, propranolol. On the triggered ventricular strip adrenaline had no effect at 6 or 15 C, but increased contraction force at 24 C. It can be suggested that in the perch heart atrium there is an activity balance of alpha and beta receptors, which mediate the negative and positive inotropic control, respectively. As in higher vertebrates, alpha adrenergic activation decreases and beta activation increases by agonists in the following order: noradrenaline, adrenaline and isoprenaline. The balance changes towards increased beta activity when temperature rises.

Temperature acclimation of the perch Perc fluviatilis L.): Changes in duration of cardiac action potential

Abstract 1. 1. Temperature acclimation for the duration of transmembrane action potential (AP) of heart ventricle was studied in vitro in the perch in winter, spring and autumn when the animals were acclimated to 2–6°C, but acclimated in the laboratory to 5 and 16°C up to 5 weeks. 2. 2. Warm acclimation caused shortening of the AP at high temperatures. Acclimation was of Prossers type III, rotation with an intersecting point at about 7°C. In warm acclimated fish the temperature dependency was greater than in cold acclimated fish. 3. 3. Warm acclimation shown in the duration of the AP was more pronounced in winter and spring than in autumn. 4. 4. It is concluded that the annual rhythm of the physiological state of eurythermic fish is an important factor for temperature acclimation.

Effect of forced motility on the noradrenaline and 5-hydroxytryptamine metabolism in different parts of the rat brain

The levels of 5-HT and 5-HIAA in the rat brain were measured after 1, 6, 24 and 36 h of forced motility in a treadwheel. The results showed that 5-HT metabolism had already increased in the forebrain after 1 h of exercise but later also increased in the brain stem, especially in the mesencephalon-pons-medulla regions. These changes had almost entirely disappeared after 50 min of rest. The NA levels with and without monoamine oxidase inhibitor were measured in animals after 36 h of forced motility. The results indicated an increase in NA metabolism in the brain stem.

The compensation of atpase activities in brain and kidney microsomes from cold and warm-acclimated carp (Cyprinus caprio L.)

1. 1.|Temperature acclimation of carp (Cryrinus carpio L). had no effect upon the specific activities or Arrhenius plots ot the Mg2+ ATPase or the Na+K+ ATPase of their brain microsome preparations. 2. 2.|The Na+-K+ ATPase activities of kidney microsomes isolated from 10 C acclimated carp was approximately one third greater than in kidney microsomes from 20 C acclimated carp. By contrast, Mg2+ ATPase of 10°C acclimated carp was approximately one third smaller than in 20 C acclimated carp. 3. 3.|Substrate affinities of Mg2+ ATPase and Na+K+ ATPase were dependent on incubation temperature of enzymes: apparent Km-values were smaller, (greater substrate affinities) at higher incubation temperature. 4. 4.|Acclimation to different temperatures had no effect upon the apparent Km for ATP of the Mg2+ ATPase or Na+K+ ATPase in either brain or kidney microsome preparations. 5. 5.|Kidney microsomes but not brain microsomes, therefore, exhibit a partial compensation of Na+K+ ATPase activity and in inverse compensation of Mg2+ ATPase activity for altered acclimation temperature. The significance and possible mechanisn of this response is discussed.

The ability of isolated myocardial cells of the rat to contract at temperatures near freezing point

Abstract 1. 1.|Single spontaneously-beating myocardial cells were prepared by enzymatic isolation from rat heart ventricles. Using a TV camera and videotape recorder, beating parameters were characterized with respect to temperature. 2. 2.|The cells obtained showed two types of contractions: (a) action-potential-coupled, fast contractions, which could be triggered electrically but sometimes also occurred spontaneously; and (b) a phasic type of contraction which occurs spontaneously as a slowly (25–200 μm s −1 ) proceedings wave through the cell and is not coupled to the action potential. 3. 3.|Both the spontaneous phasic and electrically-triggered fast contractions continued down to about 0°C, where the cells went into an irreversible contracture, but recovered if the temperature was raised before the contracture occurred. 4. 4.|In physically-contracting cells, the beat rate and the velocity of the contraction wave were temperature dependent showing a linear relationship on an Arrhenius plot; apparent activation energies were 31 and 54 kJ mol −1 , respectively. 5. 5.|When fast contractions were triggered by electric field stimulation, the threshold of cells was reduced as temperature rose. The rheobase values showed that cell excitability decreased more steeply when the temperature fell below 20°C. This change could not be seen in the values of chronaxie, which showed a linear relationship on the Arrhenius plot within the whole temperature range used (6–35°C). 6. 6.|It is concluded that the lower temperature limit is not the same for all structural levels of the rat heart. Myocardial cells are able to contract still at the freezing point while mechanisms initiating the heart beat require higher temperatures to be functional.

The effects of temperature and adrenergic agonists on cardiac myocytes of perch (Perca fluviatilis) in cell culture conditions

Abstract 1. 1. Isolated cardiac myocytes of perch, Perca fluviatilis , were kept in culture conditions for 1–2 months at 12 or 22°C. In the culture most myocytes flattened, lost their spindle-shaped morphology, protruded pseudopod-like branches and many of them started visible contractions in 1–2 weeks and continued beating for several months. Myocytes did not divide in the sparse cell population used. Typical intracellular structures could be seen in electron micrographs still after 1–2 months, but the sarcoplasmic organization became gradually more irregular in the culture. 2. 2. Beat rates showed linear temperature relationship on the Arrhenius plot. Myocytes cultivated at 22°C showed higher frequencies and slightly less dependence on temperature than myocytes cultivated at 12°C (apparent activation energies ( E a ) 86 and 107 kJ/mol, respectively). 3. 3. Temperature dependence of frequencies was related to the presence of added serum or adrenergic agonists: β-adrenergic agonists increased the frequencies and rendered the cells less dependent on temperature; apparent activation energy was 43 kJ/mol for isoprenaline or adrenaline and 108 kJ/mol for noradrenaline and control group. 4. 4. Heat tolerance was greater in myocytes cultivated at 22°C than in myocytes cultivated at 12°C, and the change in tolerance appeared in 12 h after the alteration of culture temperature and the increased tolerance was persistent after that. 5. 5. It is suggested, that the processes of quick heat-hardening and of slower but persistent heat resistance acclimation developed in these cells in culture conditions but not the capacity acclimation, which seems to be dependent on adrenergic regulation of beat rate.