β-Receptors and stress protein 70 expression in hypoxic myocardium of rainbow trout and chinook salmon

Abstract

We examined the in vivo effect of acute hypoxemia on myocardial cell-surface (sarcolemmal) β-adrenoreceptor density (Bmax) and binding affinity ( K D) and on stress protein 70 (sp70) expression by exposing rainbow trout ( Oncorhynchus mykiss; 2.1–2.7 kg) to hypoxic water (3 mg/l O2) at 15°C for 6 h. This degree of hypoxia was the minimum O2 level that these trout could tolerate without losing equilibrium and struggling violently. Hypoxic exposure reduced arterial [Formula: see text]([Formula: see text]) from 98 to 26 mmHg and arterial oxygen content ([Formula: see text]) from 10.8 to 7.4 vol/100 vol, but did not elevate epinephrine and norepinephrine levels above 10 and 30 nM, respectively. Despite the substantial reduction in blood oxygen status, the Bmax and K D of myocardial cell-surface β-adrenoreceptors were unaffected by 6 h of hypoxic exposure. In addition, acute hypoxemia did not increase myocardial sp70 expression. The failure of short-term hypoxia to decrease trout myocardial β-adrenoreceptor density clearly contrasts with the established hypoxia-mediated downregulation shown for mammals. To further investigate the influence of low[Formula: see text] on salmonid myocardial β-adrenoreceptors, binding studies were performed on the spongy (continuously exposed to deoxygenated venous blood) and compact (perfused by oxygenated blood supplied by the coronary artery) myocardia of chinook salmon. The spongy myocardium has adapted to its microenvironment of continuous low[Formula: see text] by having 14% more cell-surface β-adrenoreceptors compared with the compact myocardium. There was no tissue-specific difference in K D and no evidence of sexual dimorphism in Bmax or K D. We conclude from our studies that the salmonid heart is well adapted for sustained performance under hypoxic conditions. We found that wild chinook salmon had 2.8× more cell-surface β-adrenoreceptors compared with hatchery-reared rainbow trout. This difference suggests a significant degree of plasticity exists for fish myocardial β-adrenoreceptors. The signals underlying such differences await further study, but are not likely to include moderate hypoxia and sexual dimorphism.

Effects of extracellular changes on spontaneous heart rate of normoxia-and anoxia-acclimated turtles (Trachemys scripta)

“…This finding contrasts recent findings in the anoxiaintolerant rainbow trout heart where concurrent adrenergic stimulation better protected cardiac performance during, rather than following a combined hypoxic, hyperkalemic and acidotic insult (Hanson et al, 2006). Given that ventricular ␤-adrenoreceptor density decreases with prolonged anoxia in the turtle (Hicks and Farrell, 2000b), but not during hypoxia exposure in the rainbow trout (Gamperl et al, 1998), the possibility exists that changes in turtle cardiac ␤-adrenoceptor density with prolonged anoxia exposure may be tissue specific.…”

Cardiac plasticity in fishes: environmental influences and intraspecific differences

“…In Iceland, numerous Arctic charr morphs exist that differ substantially in morphology, behaviour and life-history characteristics, and the relative ventricular mass of an anadromous population was 10-20% greater than that of a landlocked population (M. A M. Ruiz and H. Thorarensen, unpublished data). This relationship A. K. Gamperl and A. P. Farrell 2546 (Gamperl et al, 1998). between life history and heart size is opposite to that reported for Pacific salmon (Graham and Farrell, 1992), suggesting that natural selection has provided two contrasting model systems to examine intraspecific plasticity at the stock level.…”

Maximum cardiac performance and adrenergic sensitivity of the sea bassDicentrarchus labraxat high temperatures

“…For rainbow trout, an almost twofold decrease in B max to ~20·fmol·mg protein -1 and an unchanged K d with warm acclimation was reported (Gamperl et al, 1994), confirming the earlier finding (Keen et al, 1993). Gamperl et al also reported (Gamperl et al, 1998) a high B max value (58 fmol·mg·protein -1 ) for cold-acclimated chinook salmon (13°C; Oncorhynchus tshawytscha). However, interspecific differences for B max and binding affinity (K d ) can be considerable among fish species (Olsson et al, 2000) and temperature acclimation had no effect on B max of the tropical African catfish Clarias gariepinus, although K d increased significantly at an acclimation temperature of 32°C compared with 15°C and 22°C (Hanson et al, 2005).…”