Jaakko Haverinen

University of Eastern Finland | UEF · Department of Environmental and Biological Sciences

Acclimatization of certain ectothermic vertebrates to winter conditions is associated with reduced energy consumption (winter dormancy). Principally, this may be achieved by reducing movement activity, depression of basal cellular functions, or by switching from aerobic to anaerobic energy production to sustain low energy consumption during anoxia....

https://www.sciencedirect.com/science/article/abs/pii/B9780323908016000409?via%3Dihub

Heavy metals are harmful to aquatic animals by disrupting their ionic balance. Here, we compare the effects of three metals, zinc (Zn), nickel (Ni) and manganese (Mn) on Na,K-ATPase activity in gills and kidneys in fish species with different ecophysiological characteristics. Crucian carp (Carassius carassius), a cold-dormant species, and rainbow t...

Na,K-ATPase activity is vital for virtually all cells of the animal body and the major consumer of cellular energy. However, Na,K-ATPase activity, the number of Na⁺ pump units, the catalytic rate of the pump, and their responses to thermal acclimation in different tissues of the same fish species have been seldom measured. Therefore, roach (Rutilus...

Acclimation of ectothermic vertebrates to winter dormancy is associated with reduced energy consumption. In principle, this may be achieved by reducing movement activity, depression of basal cellular functions or by switching from aerobic to anaerobic energy production. To this end, we determined standard (SMR), routine (RMR) and anoxic (AMR) metab...

In cardiac myocytes, the slow component of the delayed rectifier K+ current (IKs) ensures repolarization of action potential during beta-adrenergic activation or when other repolarizing K+ currents fail. As a key factor of cardiac repolarization IKs should be present in model species used for cardiovascular drug screening, preferably with pharmacol...

In cardiac myocytes, the slow component of the delayed rectifier K ⁺ current (I Ks ) ensures repolarization of action potential during beta-adrenergic activation or when other repolarizing K ⁺ currents fail. As a key factor of cardiac repolarization I Ks should be present in model species used for cardiovascular drug screening, preferably with phar...

Cadmium (Cd2+ ) is cardiotoxic to fish, but its effect on the electrical excitability of cardiac myocytes is largely unknown. To this end, we used the whole-cell patch-clamp method to investigate the effects of Cd2+ on ventricular action potentials (APs) and major ion currents in rainbow trout (Oncorhynchus mykiss) ventricular myocytes. Trout were...

Heat tolerance of heart rate in fish is suggested to be limited by impaired electrical excitation of the ventricle due to the antagonistic effects of high temperature on Na ⁺ (I Na ) and K ⁺ (I K1 ) ion currents (I Na is depressed at high temperatures while I K1 is resistant to them). To examine the role of Na ⁺ channel proteins in heat tolerance o...

Heat tolerance of heart rate in fish is suggested to be limited by impaired electrical excitation of the ventricle due to the antagonistic effects of high temperature on Na ⁺ (I Na ) and K ⁺ (I K1 ) ion currents (I Na is depressed at high temperatures while I K1 is resistant to them). To examine the role of Na ⁺ channel proteins and the lipid matri...

At critically high temperature, cardiac output in fish collapses as a result of depression of heart rate (bradycardia). However, the cause of bradycardia remains unresolved. To investigate this, rainbow trout (Oncorhynchus mykiss; acclimated at 12°C) were exposed to acute warming while electrocardiograms were recorded. From 12°C to 25.3°C, electric...

At critically high temperature, cardiac output in fish collapses as a result of depression of heart rate (bradycardia). However, the cause of bradycardia remains unresolved. To investigate this, rainbow trout (Oncorhynchus mykiss; acclimated at 12°C) were exposed to acute warming while electrocardiograms were recorded. From 12°C to 25.3°C, electric...

At critically high temperature, cardiac output in fish collapses due to depression of heart rate (bradycardia). However, the cause of bradycardia remains unresolved. To this end rainbow trout (Oncorhynchus mykiss; acclimated at +12°C) were exposed to acute warming, while electrocardiograms were recorded. From +12℃ to +25.3℃, electrical excitation b...

At critically high temperature, cardiac output in fish collapses due to depression of heart rate (bradycardia). However, the cause of bradycardia remains unresolved. Here we provide a mechanistic explanation for the temperature induced bradycardia. To this end rainbow trout (Oncorhynchus mykiss; acclimated at +12°C) were exposed to acute warming, w...

Under acute temperature changes cardiac output in fish is mainly regulated by changes in heart rate. According to the hypothesis of temperature-dependent deterioration of electrical excitation (TDEE) heat-dependent depression of heart rate in fish is due to the mismatch between depolarizing Na current (INa) and repolarizing K current (IK1) of ventr...

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants in aqueous environments. They affect the cardiovascular development and function in fishes. The three‐ring PAH phenanthrene has recently been shown to impair cardiac excitation‐contraction coupling by inhibiting Ca2+ and K+ currents in marine warm‐water scombrid fishes. To see if s...

Electrical excitability (EE) is vital for cardiac function and strongly modulated by temperature and external K+ concentration ([K+]o), as formulated in the hypothesis of temperature-dependent deterioration of electrical excitability (TDEE). As little is known about EE of arctic stenothermic fishes, we tested the TDEE hypothesis on ventricular myoc...

There are several similarities and differences in electrical excitability between zebrafish and human ventricles. Major ion currents generating ventricular action potentials are largely the same in human and zebrafish hearts with some exceptions. A large T-type calcium current is unique to the zebrafish ventricle (absent in human ventricle), and tw...

Calcium (Ca) channels are necessary for cardiac excitation-contraction (e-c) coupling, but Ca channel composition of fish hearts is still largely unknown. To this end, we determined transcript expression of Ca channels in the heart of zebrafish (Danio rerio), a popular model species. Altogether 18 Ca channel α-subunit genes were expressed in both a...

Na+ channel α-subunit composition of the zebrafish heart and electrophysiological properties of Na+ current (INa) of zebrafish ventricular myocytes were examined. Eight Na+ channel α-subunits were expressed in both atrium and ventricle of the zebrafish heart. Nav1.5Lb, an orthologue to the human Nav1.5, was clearly the predominant isoform in both c...

Funny current (If), formed by hyperpolarization-activated cyclic nucleotide-gated channels (HCN channels), is supposed to be crucial for the membrane clock regulating the cardiac pacemaker mechanism. We examined the presence and activity of HCN channels in the brown trout (Salmo trutta fario) sinoatrial (SA) pacemaker cells and their putative role...

Mobilization of glycogen stores was examined in the anoxic crucian carp (Carassius carassius Linnaeus). Winter-acclimatized fish were exposed to anoxia for 1, 3, or 6 weeks at 2 °C, and changes in the size of glycogen deposits were followed. After 1 week of anoxia, a major part of the glycogen stores was mobilized in liver (79.5 %) and heart (75.6...

Temperature-induced changes in cardiac output (Q) in fish are largely dependent on thermal modulation of heart rate (fH) and at high temperatures Q collapses due to heat-dependent depression of fH. This study tests the hypothesis that firing rate of sinoatrial pacemaker cells sets the upper thermal limit of fH in vivo. To this end temperature-depen...

The effects of sustained anoxia on cardiac electrical excitability were examined in the anoxia-tolerant Crucian carp (Carassius carassius). The electrocardiogram (ECG) and expression of excitation-contraction coupling genes were studied in fish acclimatised to normoxia in summer (+18°C) or winter (+2°C), and in winter fish after 1, 3 and 6 weeks of...

Seasonal changes in physiology of vertebrate animals are triggered by environmental cues including temperature, day-length and oxygen availability. Crucian carp (Carassius carassius) tolerate prolonged anoxia in winter by using several physiological adaptations that are seasonally activated. This study examines which environmental cues are required...

PhD Thesis (Effects of temperature on the electrical excitability of fish cardiac myocytes)

Electrophysiological properties and molecular background of the zebrafish (Danio rerio) cardiac inward rectifier current (IK1) were examined. Ventricular myocytes of zebrafish have a robust (-6.7 ± 1.2 pA pF(-1) at -120 mV) strongly rectifying and Ba(2+)-sensitive (IC50 = 3.8 μM) IK1. Transcripts of six Kir2 channels (drKir2.1a, drKir2.1b, drKir2.2...

—Sturgeon (family Acipenseridae) are regarded as living fossils due to their ancient origin and exceptionally slow evolution. To extend our knowledge of fish cardiac excitability to a Chondrostei fish, we examined electrophysiological phenotype of the Siberian sturgeon (Acipenser baerii) heart with recordings of epicardial ECG, intracellular action...

Hagfishes and lampreys (order Cyclostomata) are living representatives of an ancient group of jawless vertebrates (class Agnatha). Studies on cyclostome hearts may provide insights into the evolution of the vertebrate heart and thereby increase our understanding of cardiac function in higher vertebrates, including mammals. To this end, electrical e...

The upper thermal tolerance and mechanisms of heat-induced cardiac failure in the brown trout (Salmo trutta fario) was examined. The point above which ion channel function and sinoatrial contractility in vitro, and electrocardiogram (ECG) in vivo, started to fail (break point temperature, BPT) was determined by acute temperature increases. In gener...

Aim: Cardiac contraction and relaxation are mediated by rapidly changing calcium concentration around the myofibrils. In comparison with endotherms, ectothermic hearts are more strongly dependent on extracellular calcium for contraction suggesting this trait might represent the primitive vertebrate mode of cardiac activation. This study tests the...

Evolutionary origin and physiological significance of the tetrodotoxin (TTX) resistance of the vertebrate cardiac Na(+) current (I(Na)) is still unresolved. To this end, TTX sensitivity of the cardiac I(Na) was examined in cardiac myocytes of a cyclostome (lamprey), three teleost fishes (crucian carp, burbot and rainbow trout), a clawed frog, a sna...

Seasonal changes in the activity of glycogen phosphorylase (GP), a rate-limiting enzyme of glycogen degradation, were examined in an anoxia-tolerant fish species, the crucian carp (Carassius carassius L.). In muscle and brain, the activity of GP remained constant throughout the year when tested at 25°C. In contrast, the activities of liver and hear...

Ectothermic vertebrates experience acute and chronic temperature changes which affect cardiac excitability and may threaten electrical stability of the heart. Nevertheless, ectothermic hearts function over wide range of temperatures without cardiac arrhythmias, probably due to special molecular adaptations. We examine function and molecular basis o...

Glycogen is a vital energy substrate for anaerobic organisms, and the size of glycogen stores can be a limiting factor for anoxia tolerance of animals. To this end, glycogen stores in 12 different tissues of the crucian carp (Carassius carassius L.), an anoxia-tolerant fish species, were examined. Glycogen content of different tissues was 2-10 time...

Concentration-dependent inhibition of ICa by nifedipine, a specific blocker of L-type Ca2+ channels, in crucian carp atrial myocytes. To estimate CCh's negative inotropic effect on crucian carp atrial muscle via inhibition of ICa, we sought a nifedipine concentration that causes about 30% inhibition of ICa, i.e. a dose that inhibits ICa to similar...

In the anoxia-tolerant crucian carp (Carassius carassius) cardiac activity varies according to the seasons. To clarify the role of autonomic nervous control in modulation of cardiac activity, responses of atrial contraction and heart rate (HR) to carbacholine (CCh) and isoprenaline (Iso) were determined in fish acclimatized to winter (4 degrees C,...

Ryanodine (Ry) sensitivity of cardiac contraction differs between teleost species, between atrium and ventricle, and according to the thermal history of the fish. The hypothesis that variability in Ry sensitivity of contraction is due to species-specific, chamber-specific, and temperature-related differences in the sarcoplasmic reticulum (SR) Ca(2+...

Electrical activity of the heart is assumed to be one of the key factors that set thermal tolerance limits for ectothermic vertebrates. Therefore, we hypothesized that in thermal acclimation--the duration of cardiac action potential and the repolarizing K+ currents that regulate action potential duration (APD)--the rapid component of the delayed re...

In ectotherms, compensatory changes in ion channel number and activity are needed to maintain proper cardiac function at variable temperatures. The rapid component of the delayed rectifier K+ current (IKr) is important for repolarization of cardiac action potential and, therefore, crucial for regulation of cellular excitability and heart rate. To e...

Hassinen M, Haverinen J, Vornanen M. Electrophysiological properties and expression of the delayed rectifier potassium (ERG) channels in the heart of thermally acclimated rainbow trout.—In ecto-therms, compensatory changes in ion channel number and activity are needed to maintain proper cardiac function at variable temperatures. The rapid component...

Sodium current (I(Na)) of the mammalian heart is resistant to tetrodotoxin (TTX) due to low TTX affinity of the cardiac sodium channel (Na(v)) isoform Na(v)1.5. To test applicability of this finding to other vertebrates, TTX sensitivity of the fish cardiac I(Na) and its molecular identity were examined. Molecular cloning and whole-cell patch-clamp...

Potassium currents are plastic entities that modify electrical activity of the heart in various physiological conditions including chronic thermal stress. We examined the molecular basis of the inward rectifier K+ current (IK1) in rainbow trout acclimated to cold (4 degrees C, CA) and warm (18 degrees C, WA) temperature. Inward rectifier K+ channel...

The hypothesis of pacemaker level origin of thermal compensation in heart rate was tested by recording action potentials (AP) in intact sinoatrial tissue and enzymatically isolated pacemaker cells of rainbow trout acclimated at 4 degrees C (cold) and 18 degrees C (warm). With electrophysiological recordings, the primary pacemaker was located at the...

The present study examines the importance of the Na+ current (INa) in the excitability of atrial and ventricular myocardium of the rainbow trout heart. Whole-cell patch-clamp under reduced sarcolemmal Na+ gradient showed that the density of INa is similar in atrial and ventricular myocytes of the trout heart, and the same result was obtained when I...

The present study was designed to test the hypothesis that temperature acclimation modifies sarcolemmal Na+ current (INa) of the fish cardiac myocytes differently depending on the animal's lifestyle in the cold. Two eurythermal fish species with different physiological strategies for surviving in the cold, a cold-dormant crucian carp (Carassius car...