Aims: to investigate α2-AR subtype distribution and the relationship between receptor amounts and their functionality in normotensive and spontaneously hypertensive rats.
Methods: experiments were performed on left ventricular cardiomyocytes isolated from Wistar rats and SHR (2-2.5 months). Molecular routine tools (RT-PCR, Western blotting, immunocytochemistry) were used for semi-quantitative estimation of α2-AR subtypes. Fluorescence of both the Ca2+-dependent and NO-sensitive probes were used to define functionality of α2-AR, evaluated by changes in the dynamics of spontaneous Ca2+-transients and NO production in cardiomyocytes in response to the α2-AR agonist application.
Results: percentage of the three known α2-AR subtypes in Wistar and SHR cardiomyocytes is not principally different. Total amounts of α2A-AR subtype in SHR increases, for both the sarcolemmal and intracellular receptor pools. Total number of α2B-AR is also significantly higher in hypertensive rats with an increase in the sarcolemmal, but not the intracellular immunoreactivity. For α2C-AR subtype, no significant differences between Wistar and SHR were identified, despite the fact that its amounts in cardiomyocytes are somewhat higher than the other two subtypes. Notwithstanding the increased expression of α2-AR subtypes in SHR, α2-AR-agonist guanabenz was ineffective in suppression of spontaneous Ca2+-transients, as well as the lowering of free calcium levels in the cytosol. Guanabenz-induced NO synthesis is well correlated with the Ca2+-loading into sarcoplasmic reticulum and actually decreased in SHR cardiomyocytes.
Conclusion: data indicate α2-AR dysfunction and ineffectiveness of α2-AR-mediated signaling pathways in this model of cardiovascular pathologies. Results can be used for clinical practice for more effective control of cardiovascular functions in various disease states.
Keywords: Agmatine; Guanabenz; Nitric oxide; SERCA; Spontaneous Ca(2+)-transients.
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