Ca²⁺ leakage rate from agonist-sensitive intracellular pools is altered in platelets from patients with type 2 diabetes

Abstract

Platelets from patients with type 2 diabetes show abnormalities in intracellular Ca²⁺ homeostasis that are involved in platelet hyperaggregability and the development of thrombotic complications. Different Ca²⁺ transport mechanisms have been reported to be altered in platelets from patients with type 2 diabetes, including the sarcoendoplasmic and plasma membrane Ca²⁺-ATPases, plasma membrane Ca²⁺ channels, or the Na⁺/Ca²⁺ exchanger. Here, we have investigated whether passive Ca²⁺ leak from the stores is altered in platelets from patients with type 2 diabetes. Resting cytosolic Ca²⁺ concentration ([Ca²⁺]_i) was found to be greater in platelets from patients with type 2 diabetes than in healthy controls. In a Ca²⁺-free medium, platelet stimulation with thrombin or ADP evokes a rapid and transient increase in [Ca²⁺]_i that was found to be greater in patients with diabetes than in healthy controls. Sequential or combined inhibition of Ca²⁺ extrusion and Ca²⁺ sequestration into the stores reduced the difference between the responses to agonists in patients with diabetes and healthy controls, although agonist-induced Ca²⁺ efflux from the stores was still significantly greater in patients with diabetes. Ca²⁺ leak from the dense tubular system or the acidic stores, induced by a low concentration of thapsigargin or 2,5-di-(t-butyl)-1,4-hydroquinone (TBHQ), respectively, was clearly greater in patients with diabetes than in controls, and was not significantly modified by treatment with 2-APB. These findings indicate that passive Ca²⁺ leakage rate from the intracellular stores in platelets is significantly enhanced in patients with type 2 diabetes mellitus and this might explain the increased resting [Ca²⁺]_i.

• Thrombin
• ADP
• calcium leakage
• platelets
• intracellular stores