α2-Adrenoceptor signaling in cardiomyocytes of spontaneously hypertensive rats starts to impair already at early age

alpha 2-Adrenoceptors (alpha 2-AR) found in the cardiomyocyte's sarcolemma represent a very important negative feedback for control of myocardial contractility by endogenous catecholamines. Earlier, we showed that the endogenous neurotransmitter agmatine in micromolar concentrations via alpha 2-AR activates the nitric oxide (NO) synthesis, enhancing the Ca2+ pumping into sarcoplasmic reticulum (SR). In the millimolar doses it inhibits Ca2+ sequestration by SR Ca2+ ATPase (SERCA), acting through the first type of imidazoline receptors. Here, we study the functional activity of agmatine, as well as a specific alpha 2-agonist, guanabenz, in respect to spontaneous Ca2+-transients in SHR cardiomyocytes of the early age (2-2.5 months), and adulthood animals (8-9 months). alpha 2-mediated cardioprotective effect was almost twofold decreased in SHR cardiac cells compared to normotensive rats of the corresponding age, despite the fact that both alpha 2A- and alpha 2B-AR protein levels were significantly increased in SHR cardiomyocytes. NO-mediated facilitation of SERCA activity is substantially reduced in SHR cardiomyocytes vs. normotensive rats. These data suggest that the SHR phenotype starting from early age shows signs of the impaired sarcolemmal alpha 2-AR signaling, which can aggravate the development of this cardiovascular pathology. (C) 2019 Elsevier Inc. All rights reserved.