Cellular sodium membrane transport and cardiovascular risk factors in non-insulin-dependent diabetes mellitus

Intracellular calcium and sodium-lithium countertransport in type 2 diabetic patients with and without albuminuria

Increased intracellular calcium concentrations ([Ca(2+)](i)) and enhanced sodium-lithium countertransport (Na/Li CT) activities may play a role in the development of diabetic complications such as diabetic nephropathy. The present study was designed to test the hypothesis that albuminuria in patients with type 2 diabetes is associated with increased [Ca(2+)](i) in response to stimulation with platelet-activating factor (PAF) or with enhanced Na/Li CT activities. The study population comprised 203 type 2 diabetic patients. Albuminuria was defined as an albumin excretion rate exceeding 30 mg/d (117 cases). PAF-evoked rises in [Ca(2+)](i) and Na/Li CT activities were determined in Epstein-Barr-virus-immortalized lymphoblasts. Albuminuria was related to high stimulated [Ca(2+)](i) but not to high basal [Ca(2+)](i). The association was independent of age, sex and several non-diabetes related confounders, but depended on diabetes-related factors, such as the duration of diabetes. The risk of albuminuria was highest in subjects with high [Ca(2+)](i) who reported a diabetes duration of < or =10 years. There was no association between Na/Li CT activities and albuminuria. The present results support the hypothesis that albuminuria in type 2 diabetic patients is associated with a primary defect in intracellular calcium homeostasis. The association between stimulated [Ca(2+)](i) and albuminuria is most prominent in early diabetes.

Platelet sodium-proton exchanger and phospholipid-dependent procoagulant activity in patients with type 2 diabetes

Platelet Na(+)/H(+) exchanger (NHE) activity, phospholipid-dependent thrombin generation, and platelet factor 3 (PF3) availability were measured in 83 type 2 diabetics and in 40 age- and sex-matched healthy subjects. Na(+)/H(+) exchanger activity was significantly increased in diabetic patients in comparison to the controls (kappa = 4.29 +/- 0.71 x 10(-3) x s(-1) v 3.21 +/- 0.64 x 10(-3) x s(-1), P <.00001). However, there was no significant difference between subjects with (kappa = 4.28 +/- 0.75 x 10(-3) x s(-1)) and without (kappa = 4.26 +/- 0.32 x10(-3) x s(-1)) arterial hypertension, as well as between patients with normo- and microalbuminuria or overt proteinuria (kappa = 4.26 +/- 0.58 x 10(-3) x s(-1), kappa = 4.47 +/- 0.93 x 10(-3) x s(-1) and kappa = 4.07 +/- 0.38 x10(-3) x s(-1), respectively). Comparatively high NHE activity was observed in the group of patients with hemoglobin A(1c) (HbA(1c)) less than 7.5%. Multiple regression analysis revealed that the factors independently related to platelet Na(+)/H(+) exchanger activity were: total PF3 activity (beta = 0.77, P =.011) and triglyceride (TG) concentration (beta = 0.44, P =.039). Phospholipid-dependent thrombin generation and PF3 availability were also enhanced in all plasma fractions of diabetic patients, especially in platelet-poor plasma (PPP) and platelet-free plasma (PFP) (P <.0001 and P <.00001, respectively). There was a positive correlation between NHE activity and thrombin generation, as well as with PF3 availability in all plasma fractions. Our results suggest that enhanced platelet Na(+)/H(+) exchanger activity associated with raised phospholipid-dependent procoagulant activity may increase the risk of vascular damage in type 2 diabetic patients.

Hypertension and nephropathy in diabetes mellitus: what is inherited and what is acquired?

Prolonged duration of diabetes mellitus, poor long term glycemic control and raised blood pressure have all been clearly related to the development of diabetic nephropathy. Evidence exists to suggest that a subset of individuals with diabetes have a genetic predisposition to diabetic nephropathy. Cases of diabetic nephropathy cluster in families and a parental history of hypertension is more common in patients with diabetic nephropathy. Current evidence suggests an important role for hypertension in the genetic susceptibility to diabetic nephropathy but the extent of this is unknown. While cellular and animal studies have generated a plethora of data regarding mechanisms involved in the role of hypertension and diabetic nephropathy, these are not helpful for drawing conclusions in humans. In the following review, we examine the available clinical, epidemiologic and family studies to assess the relationship between the development of hypertension and diabetic nephropathy in IDDM and NIDDM. We will demonstrate the differences in the epidemiology of hypertension in diabetes depending on the type of diabetes and thus, move the emphasis of nephropathy susceptibility away from hypertension per se. We hope to emphasize instead the homogeneity of nephropathy risk in both IDDM and NIDDM and also the idea that a common genetic susceptibility exists for all types of diabetes and is conditional on cumulative exposure to hyperglycemia. Regarding the interaction of hypertension and nephropathy in diabetes mellitus, any conclusions at this time about what is inherited and what is acquired must be regarded as speculative. However we will discuss some potential mechanisms of hypertension in the evolution of nephropathy and we will allude to the role for novel genetic studies in the search for nephropathy susceptibility gene(s).