Background Asymptomatic diabetic patients have a high incidence of clinically unrecognized left ventricular dysfunction with an abnormal cardiac response to exercise. We, therefore, examined subclinical defects in the contraction-relaxation cycle and intracellular Ca(2+) regulation in myocardium of asymptomatic type 2 diabetic patients. Methods Alterations in the dynamics of the intracellular Ca(2+) transient and contractility were recorded in right atrial myocardium of type 2 diabetic patients and non-diabetic control tissue loaded with fura-2. In order to gain an insight into mechanisms underlying the altered Ca(2+) handling in diabetic myocardium levels of mRNA, protein expression and phosphorylation of key proteins in sarcoplasmic Ca(2+) handling were determined. Results In isolated atrial trabeculae of diabetic myocardium the rise of systolic Ca(2+) was significantly prolonged, but relaxation of the Ca(2+) transient was unaltered compared to control tissue. Accordingly, the levels of expression of mRNA and protein of the Ca(2+) release channel (RyR2) of the sarcoplasmic reticulum were reduced by 68 and 22%, respectively. Endogenous phosphorylation of RyR2 by protein kinases C, however, was increased by 31% in diabetic myocardium, as assessed by the back-phosphorylation technique. Levels of expression of SERCA2 and phospholamban were unaltered between both groups. Conclusions Intracellular Ca(2+) release is prolonged in non-failing myocardium of type 2 diabetic patients and this may be primarily due to a decreased expression of RyR2. This defective Ca(2+) release may represent an early stage of ventricular dysfunction in type 2 diabetes and would favor the abnormal response to exercise frequently observed in asymptomatic diabetic patients.

The frequency of duplicated and non-expressed C4 alleles was determined by segregation analysis in 31 German and five French families with altogether 274 individuals by submitting the complete data from C4 protein phenotyping, including C4 beta chains, and the other classical MHC markers to the family analysis programme (FAP). From 120 unrelated German haplotypes the following frequencies were derived for silent alleles: C4A*Q0 0.2000, C4B*Q0 0.2083, and for the total of homo- and heteroduplicated C4A resp. C4B alleles: C4"DA"* 0.1333, C4"DB"* 0.1000. The true occurrence of the duplicated C4A*2, "DB*21" haplotype, first observed in French families, was found to be 0.0250 in the German sample. While the frequency of duplicated C4 haplotypes confirms earlier estimates, the increase in the frequency of silent alleles corresponds to those assumed from investigations at the DNA level. The results demonstrate classical protein typing with inclusion of C4 beta chain types to be an indispensable and powerful tool for haplotype recognition; they support the hypothesis that deletion at one C4 locus is accompanied by duplication at the other in a majority of haplotypes.

Aims/hypothesis The angiotensin II (type 1) (AT1) receptor mediates many biological effects of the renin-angiotensin system (RAS), leading to remodelling of cardiac tissue. The present study was designed to analyse changes in the function and expression of the AT1 receptor as principal effector of the RAS in myocardium from type 2 diabetic patients compared with non-diabetic myocardium as control. In addition, we determined the effect of treatment with ACE inhibitors or AT1 receptor blockers on expression levels of the receptor in diabetic patients. Methods Gene expression of the AT1 receptor was analysed by quantitative RT-PCR and protein expression was determined by immunoblot analysis in human right atrial myocardium. We investigated functional coupling of the receptors by measuring contractility in isolated trabeculae stimulated with increasing concentrations of angiotensin II. Results Diabetic myocardium showed a significant increase in protein expression (170±16% of control) and median mRNA expression (186% of control) of the AT1 receptor.The additional receptors were functionally coupled, resulting in a stronger inotropic response upon stimulation with angiotensin II (89±5.5% vs 29±1.6% in controls), whereas receptor affinity was similar in both groups. However, myocardium from diabetic patients treated with ACE inhibitors or AT1 receptor blockers showed no increase in AT1 receptor expression. Conclusions/interpretation AT1 receptor expression in myocardium of type 2 diabetic patients is dynamic, depending on the level of glycaemic control and the activity of the RAS. These findings could at least in part explain the strong therapeutic benefit of RAS inhibition in diabetic patients.

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