Hypercapnic Acidosis Reduces Contractile Function in the Ventricle of the Armored Catfish,Pterygoplichthys pardalis

Abstract

The armored catfish, Pterygoplichthys pardalis (formerly Liposarcus pardalis), is a freshwater, facultative air-breathing teleost that experiences seasonal hypercapnia in the water systems of South America. We studied the tolerance of the P. pardalis heart to hypercapnic acidosis using an isolated ventricular muscle strip preparation. Force generation and kinetic variables were examined across a range of contraction frequencies under normocapnic and hypercapnic conditions in the absence and presence of sarcoplasmic reticulum (SR) inhibitors. Pterygoplichthys pardalis ventricle exhibited robust contractile force, on par with athletic fish species such as trout and tuna and a relatively flat force-frequency relationship between 0.2 and 1.5 Hz under normocapnic conditions (1% CO2, pH 7.78 +/- 0.02). Hypercapnic acidosis (7.5% CO2, pH 7.78 +/- 0.03) did not alter the shape of the force-frequency response but reduced force by approximately 50% across all frequencies tested, with only partial recovery upon return to normocapnic conditions. A subsequent and more severe acidotic challenge (15% CO2, pH 6.77 +/- 0.05) caused an additional 20% decrease in force. Force recovered to the level at which it had stablized after the first hypercapnic insult. SR inhibition had no steady state effect on force production at 0.2 Hz but resulted in a negative force-frequency relationship, suggesting that SR Ca2+ is recruited to a greater extent at high contraction frequencies. Surprisingly, SR-inhibited muscle was more resistant to hypercapnic acidosis (force decreased by approximately 40% across all frequencies) and displayed improved recovery upon return to normocapnic conditions. The significance of this latter finding is not clear. In aggregate, our results demonstrate robust contractile force, which extends across a range of frequencies and appears to be supported by SR Ca2+ cycling. Hypercapnic acidosis reduced contractile force but may provide preconditioning-like protection from subsequent insults.

Increased ventricular stiffness and decreased cardiac function in Atlantic cod (Gadus morhua) at high temperatures

“…However, our data suggest that the ventricular muscle of Atlantic cod does not follow this pattern, as has also been observed for some other species (47). Developed isometric twitch force at 20°C increased with contraction frequency up to about 90 contractions/ min, and the product of force and frequency was maximal at more than 110 contractions/min, being about double that measured at slower heart rates (Figs.…”

“…The isometric force developed by Atlantic cod ventricular trabeculae (ϳ6 kN/m 2 at both 10 and 20°C) is within the range of values reported for trabeculae from other fish species at comparable temperatures, including armored catfish [6 kN/m 2 at 25°C(47)] and rainbow trout [1.6 kN/m 2 at 12°C (44), 4 kN/m 2 at 10 and 22°C(21,48), and 22 kN/m 2 for compact myocardium at 15°C(25)], although there is considerable variability in the rainbow trout data between studies and heart muscle type. Isometric force developed by Atlantic cod atrial trabeculae (ϳ2.5 kN/m 2 at 10°C and 3 kN/m 2 at 20°C) is less than the values reported for yellowfin tuna (Thunnus albacares) at cooler temperatures (18 kN/m 2 at 15°C and 15 kN/m 2 at 18°C) but closer to values at Shortening work (o and OE), lengthening work (p and ), and net work (OE and ) done by Atlantic cod ventricular trabeculae at 20°C and different oxygen pressures during 5 min of repeated contractions.…”

The effects of endogenous and exogenous catecholamines on hypoxic cardiac performance in red‐bellied piranhas

“…Piranhas exhibited the typical negative piscine force–frequency relationship (Shiels, Vornanen, & Farrell, ). However, similar to other tropical fish, some of which exhibit flat force–frequency relationships (Shiels, Santiago, & Galli, ), this relationship was not steep. If red‐bellied piranhas develop a hypoxic bradycardia similar to the closely related pacu (approximately 60–36 beats/min; 1–0.6 Hz), this would have a rather modest impact on contractile force (5% increase; based on the first force–frequency trial in untreated hypoxic preparations).…”

Interrelationship Between Contractility, Protein Synthesis and Metabolism in Mantle of Juvenile Cuttlefish (Sepia officinalis)

“…Tension measurements were normalized to absolute stress using the nominal cross-sectional area of the preparation and an assumed muscle density of 1.06 g cm –3 (Layland and Altringham, 1995), as previously described (Shiels et al, 2010). Each data point represents the mean of at least three representative contractions.…”