Repeated immobilization stress reduces the gene expression of the type 1 and 2 IP3 receptors in stellate ganglia

Adrenergic and calcium modulation of the heart in stress: from molecular biology to function

There is strong evidence about the importance of catecholamines and calcium signaling in heart function. Also, interaction of these two systems is well documented. Catecholamines signal through adrenergic receptors, and further activate calcium transport either from the extracellular space, or from the intracellular calcium stores. This review summarizes current knowledge on catecholamine production in the heart, with special focus on the final enzyme in the catecholamine synthesizing pathway, phenylethanolamine N-methyltransferase (PNMT), in different cell types in the heart. Further, signaling through different types of adrenergic receptors in physiological conditions and after exposure to different stressors is discussed. Also, part of this review considers activation of an intracellular calcium transport system via inositol 1,4,5-trisphosphate receptor and to possible functional consequences in control and stress conditions.

Adrenergic modulation of the type 1 IP3 receptors in the rat heart

Inositol 1,4,5-trisphosphate (IP3) receptors are calcium-releasing channels localized on the sarcoplasmic reticulum. IP3 receptors mediate the calcium mobilizing effect of a wide range of hormones, cytokines, and neurotransmitters and play an important role in variety of cell functions. The aim of this work was to study, how partial depletion of catecholamines affects the gene expression and protein levels of the type 1 IP3 receptors in rat heart. The type 1 IP3 receptor mRNA levels were studied in the left cardiac atrium and ventricle of rats treated with 6-hydroxydopamine (6-OHDA) in control and stressed conditions. The 6-OHDA produces anatomical and functional denervation resulting in decreased levels of noradrenaline and adrenaline. We also used corticoliberin (CRH) knockout mice, where secretion of adrenaline is significantly suppressed. Administration of 6-OHDA significantly decreases mRNA levels of the type 1 IP3 receptor in both, the left atrium and the left ventricle, while the gene expression of the sarcoplasmic reticular Ca2+-ATPase (SERCA 2) was unaffected. CRH knockout mice possess markedly lower levels of the type 1 IP3 receptor mRNA compared to wild-type mice in both, control and stressed conditions. These data point to the adrenergic modulation of the type 1 IP3 receptors in the rat hearts.

Repeated immobilization stress decreases mRNA and protein levels of the type 1 IP3 receptor in rat heart

Stress is one of the major contributors to the development of cardiovascular disorders and psychiatric illnesses. Immobilization stress belongs to severe stressors and is known to activate several calcium transport systems. The aim of this work was to determine whether repeated immobilization stress changes mRNA and protein levels of the type 1 and 2 inositol-1,4,5-trisphosphate (IP(3)) receptors in cardiac tissue. Rats were immobilized for 7 days, 2 h daily. After repeated immobilization, increased numbers of collagen fibers were accumulated in the heart atria compared to hearts of the control group of rats. Gene expression was determined after reverse transcription and subsequent real-time polymerase chain reaction, using SYBR Green fluorescent dye. Protein levels were determined by Western blot and hybridization with the primary antibody against IP(3) receptors. Contrary to single immobilization, repeated immobilization decreased a gene expression of the type 1 and 2 IP(3) receptors, and also protein levels of the IP(3) receptors. Although the physiologic relevance of our observations remains to be elucidated, we propose that the decrease in IP(3) receptors may have an impact on the development of the pathophysiologic changes in the heart.

Inositol 1,4,5-Trisphosphate Receptors in the Heart Compared to Other Tissues Are Differently Modulated by Stress

IP(3) receptors are intracellular calcium channels, releasing calcium from the sarcoplasmic reticulum. In the heart, IP(3) receptors of type 1 and 2 were found. These receptors predominate in atria, although they occur also in ventricles, as determined by real-time PCR and Western blot analysis. Single-immobilization stress was found to increase mRNA and/or protein levels of types 1 and 2 IP(3) receptors in cardiac atria. However, in stellate ganglia, which innervate the heart, no changes in the mRNA of the type 1 IP(3) receptors were observed after single-immobilization stress. In adrenal medulla, a moderate decrease in both mRNA and protein levels of IP(3) receptors was observed after single-immobilization exposure. After repeated immobilization, mRNA and protein levels of types 1 and 2 IP(3) receptors decreased significantly in all tested tissues. Our results point to different processing of the single stress in different tissues, while repeated stress results in rapid and significant decrease of the IP(3) receptors.