Biology subjects

Vornanen, M.

Publications and source records attributed to Vornanen, M..

3 recordsLinked to original sources

bioRxiv2021

Effect of channel assembly (KCNQ1 or KCNQ1 + KCNE1) on the response of zebrafish IKs to IKs inhibitors and activators

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 pharmacological characteristics similar to those of the human IKs. To this end, we investigated the effects of inhibitors and activators of the IKs on KCNQ1 and KCNQ1+KCNE1 channels of the zebrafish, an important model species, in Chinese hamster ovary cells. Inhibitors of IKs, chromanol 293B and HMR-1556, inhibited zebrafish IKs channels with approximately similar potency as that of mammalian IKs. Chromanol 293B concentration for half-maximal inhibition (IC50) of zebrafish IKs was at 13.1{+/-}5.8 and 13.4{+/-}2.8 M for KCNQ1 and KCNQ1+KCNE1 channels, respectively. HMR-1556 was a more potent inhibitor of zebrafish IKs with IC50=0.1{+/-}0.1 M and 1.5{+/-}0.8 M for KCNQ1 and KCNQ1+KCNE1 channels, respectively. R-L3 and mefenamic acid, generally identified as IKs activators, both inhibited zebrafish IKs. R-L3 almost completely inhibited zebrafish IKs generated by KCNQ1 and KCNQ1+KCNE1 channels with similar affinity (IC50 1.1{+/-}0.4 and 1.0{+/-}0.4 M, respectively). Mefenamic acid partially blocked zebrafish KCNQ1 (IC50=9.5{+/-}4.8 M) and completely blocked KCNQ1+KCNE1 channels (IC50=3.3{+/-}1.8 M). Although zebrafish IKs responds to IKs inhibitors in the same way as mammalian IKs, its response to activators is atypical, probably due to the differences in the binding domain of KCNE1 to KCNQ1. Therefore, care must be taken when translating the results from zebrafish to humans.

physiology↗

bioRxiv2020

Effects of Na+ channel isoforms and lipid membrane environment on temperature tolerance of cardiac Na+ current in zebrafish (Danio rerio) and rainbow trout (Oncorhynchus mykiss)

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+ (INa) and K+ (IK1) ion currents (INa is depressed at high temperatures while IK1 is resistant to them). To examine the role of Na+ channel proteins and the lipid matrix of the channels in heat tolerance of INa, we compared temperature-dependencies of zebrafish (Danio rerio) and rainbow trout (Oncorhynchus mykiss) ventricular INa, and INa generated by the cloned zebrafish and rainbow trout NaV1.4 and NaV1.5 Na+ channels in HEK cells. Whole-cell patch clamp recordings showed that zebrafish ventricular INa has better heat tolerance and slower inactivation kinetics than rainbow trout ventricular INa. In contrast, heat tolerance and inactivation kinetics of zebrafish and rainbow trout NaV1.4 channels are similar when expressed in the identical plasma membrane lipid matrix of HEK cells. The same applies to NaV1.5 channels. Thermal adaptation of the ventricular INa is largely achieved by differential expression of Na+ channel alpha subunits: zebrafish which tolerate well high temperatures mainly express the slower NaV1.5 isoform, while rainbow trout which prefer cold waters mainly express the faster NaV1.4 isoform. Differences in elasticity (stiffness) of the lipid bilayer may be also involved in thermal adaptation of INa. These findings suggest that both the protein component and its lipid bilayer matrix are involved in thermal adaptation of the voltage-gated Na+ channels and therefore in heart rate regulation under thermal stress in fish.

physiology↗

bioRxiv2020

Depression of heart rate in fish at critically high temperatures is due to atrioventricular block

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{degrees}C) were exposed to acute warming, while cardiac function was followed from electrocardiograms. From +12{degrees}C to +25.3{degrees}C, electrical excitation between different parts of the heart was coordinated but above +25.3{degrees}C atrial and ventricular beating rates became partly dissociated due to 2:1 atrioventricular (AV) block. With further warming atrial rate increased to the peak value of 188 {+/-} 22 bpm at +27{degrees}C, while the rate of the ventricle reached the peak value of 124 {+/-} 10 bpm at +25.3{degrees}C and thereafter dropped to 111 {+/-} 15 bpm at +27{degrees}C. In single ventricular myocytes, warming from +12{degrees}C to +25{degrees}C attenuated electrical excitability as evidenced by increases in rheobase current and critical depolarization required to trigger action potential. The depression of excitability was caused by temperature induced decrease in input resistance (sarcolemmal K+ leak via the outward IK1 current) of resting myocytes and decrease in inward charge transfer by the Na+ current (INa) of active myocytes. Collectively these findings show that at critically high temperatures AV block causes ventricular bradycardia which is an outcome from the increased excitation threshold of the ventricle due to changes in passive (resting ion leak) and active (inward charge movement) electrical properties of ventricular myocytes. The sequence of events from the level of ion channels to the cardiac function in vivo provides a mechanistic explanation for the depression of cardiac output in fish at critically high temperature.

physiology↗