Diabetes-related defects in sarcoplasmic [Ca.sup.2+] release are prevented by inactivation of [G[alpha].sub.11] and [G[alpha].sub.q] in murine cardiomyocytes

Neurohumoral stimulation of Gq-coupled receptors has been proposed as a central mechanism in the pathogenesis of diabetic heart disease. The resulting contractile dysfunction is closely related to abnormal intracellular [Ca.sup.2+] handling with functional defects of the sarcoplasmic reticulum (SR). The present study was therefore designed to determine the role of [G.sub.q]-protein signaling via [G[alpha].sub.11] and Gaq in diabetes for the induction of functional and structural changes in the [Ca.sup.2+] release complex of the SR. An experimental type 1-diabetes was induced in wild type, [G[alpha].sub.11] knockout, and [G[alpha].sub.11/q]- knockout mice by injection of streptozotocin. Cardiac morphology and function was assessed in vivo by echocardiography. SR [Ca.sup.2+] leak was tested in vitro based on a [sup.45][Ca.sup.2+] assay and protein densities as well as gene expression of ryanodine receptor (RyR2), FKBP12.6, sorcin, and annexin A7 were analyzed by immunoblot and RT-PCR. In wild type animals 8 weeks of diabetes resulted in cardiac hypertrophy and SR [Ca.sup.2+] leak was increased. In addition, diabetic wild type animals showed reduced protein levels of FKBP12.6 and annexin A7. In [G[alpha].sub.11]- and [G[alpha].sub.11/q]-knockout animals, however, SR [Ca.sup.2+] release and cardiac phenotype remained unchanged upon induction of diabetes. Densities of the proteins that we presently analyzed were also unaltered in [G[alpha].sub.11]-knockout mice. [G[alpha].sub.11/q]-knockout animals even showed increased expression of sorcin and annexin A7. Thus, based on the present study we suggest a signaling pathway via the [G.sub.q]-proteins, [G[alpha].sub.11] and [G[alpha].sub.q], that could link increased neurohumoral stimulation in diabetes with defective RyR2 channel function by regulating protein expression of FKBP12.6, annexin A7, and sorcin. Keywords Ryanodine receptor * Type 1-diabetes * Knockout mice * Sorcin * Annexin A7