Temperature and species-specific effects on 3-adrenergic receptor cardiac regulation in two freshwater teleosts: Channel catfish (Ictalurus punctatus) and common carp (Cyprinus carpio).
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abstract
-adrenergic receptors (AR) are important in teleost cardiovascular regulation. To date, it is unknown whether temperature acclimation changes -AR functionality and consequently the involvement of this AR subtype in teleost cardiac regulation. Common carp (Cyprinus carpio) were acclimated at 12 C or 23 C (minimum 3 weeks) after which cardiovascular variables (cardiac output (Q), stroke volume (Sv) and heart rate (fH)) were measured upon injection of the -AR agonist, BRL(37344), and antagonist, SR(59230A). In both 12 C and 23 C acclimated carp, BRL(37344) induced significant increases in fH and Q whereas Sv was significantly decreased. While temperature did not affect the change (increase vs. decrease) in cardiac variables, the magnitude and on-set of responses differed. For instance, fH, Sv and Q responded significantly faster to -AR stimulation in 23 C carp. In contrast, maximum responses of fH and Q were significantly higher in 23 C carp whereas the maximum response of Sv was significantly greater in 12 C carp. These findings suggest that temperature acclimation induced changes in -AR receptor functionality (e.g. density and/or affinity). Stimulation of -ARs in 23 C acclimated channel catfish (Ictalurus punctatus) caused significant increases in fH, Sv and Q. The increase in Sv was opposite to the decrease observed in 23 C acclimated common carp. SR(59230A) induced significant decreases in Sv and Q but had no effect in carp (23 C). Results suggest species diversity in the density and affinity or structure of -ARs which may explain the different cardiac responses to -AR ligands.
