Department of Ocean Sciences and Biology, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
Am J Physiol Regul Integr Comp Physiol. 2021 May 1;320(5):R588-R610. doi: 10.1152/ajpregu.00014.2020. Epub 2021 Jan 27.
Whether hypoxic acclimation influences nitric oxide (NO)-mediated control of fish cardiac function is not known. Thus, we measured the function/performance of myocardial strips from normoxic- and hypoxic-acclimated (40% air saturation; ∼8 kPa O) trout at several frequencies (20-80 contractions·min) and two muscle strain amplitudes (8% and 14%) when exposed to increasing concentrations of the NO donor sodium nitroprusside (SNP) (10 to 10 M). Further, we examined the influence of ) nitric oxide synthase (NOS) produced NO [by blocking NOS with 10 M -monomethyl-l-arginine (l-NMMA)] and ) soluble guanylyl cyclase mediated, NOS-independent, NO effects (i.e., after blockade with 10 M ODQ), on myocardial contractility. Hypoxic acclimation increased twitch duration by 8%-10% and decreased mass-specific net power by ∼35%. However, hypoxic acclimation only had minor impacts on the effects of SNP and the two blockers on myocardial function. The most surprising finding of the current study was the degree to which contraction frequency and strain amplitude influenced NO-mediated effects on myocardial power. For example, at 8% strain, 10 SNP resulted in a decrease in net power of ∼30% at 20 min but an increase of ∼20% at 80 min, and this effect was magnified at 14% strain. This research suggests that hypoxic acclimation has only minor effects on NO-mediated myocardial contractility in salmonids, is the first to report the high frequency- and strain-dependent nature of NO effects on myocardial contractility in fishes, and supports previous work showing that NO effects on the heart (myocardium) are finely tuned spatiotemporally.
低氧适应是否影响鱼类心脏功能的一氧化氮（NO）介导的控制尚不清楚。因此，我们测量了来自常氧和低氧适应（40%空气饱和度；约 8 kPa O）虹鳟鱼的心肌条在几个频率（20-80 收缩·分钟）和两个肌肉应变幅度（8%和 14%）下对增加浓度的一氧化氮供体硝普钠（SNP）（10 至 10 M）的功能/性能。此外，我们检查了一氧化氮合酶（NOS）产生的 NO 的影响[通过用 10 M -单甲基-l-精氨酸（l-NMMA）阻断 NOS]和）可溶性鸟苷酸环化酶介导的、NOS 独立的、NO 效应（即在 10 M ODQ 阻断后）对心肌收缩性的影响。低氧适应使收缩时程增加 8%-10%，并使比质量净功率降低约 35%。然而，低氧适应仅对 SNP 和两种阻断剂对心肌功能的影响产生较小的影响。当前研究最令人惊讶的发现是收缩频率和应变幅度对 NO 介导的心肌功能影响的程度。例如，在 8%应变下，10 SNP 在 20 分钟时导致净功率降低约 30%，但在 80 分钟时增加约 20%，并且在 14%应变下这种效应放大。这项研究表明，低氧适应对鲑鱼科鱼类的 NO 介导的心肌收缩性仅有较小的影响，首次报道了鱼类心肌收缩性中高频和应变依赖性的 NO 效应，并且支持先前的工作表明，NO 对心脏（心肌）的影响在时空上是精细调节的。
