Elevated Ca²⁺ sparklet activity during acute hyperglycemia and diabetes in cerebral arterial smooth muscle cells

Abstract

Ca(+) sparklets are subcellular Ca(2+) signals produced by the opening of L-type Ca(2+) channels (LTCCs). In cerebral arterial myocytes, Ca(2+) sparklet activity varies regionally, resulting in low and high activity, "persistent" Ca(2+) sparklet sites. Although increased Ca(2+) influx via LTCCs in arterial myocytes has been implicated in the chain of events contributing to vascular dysfunction during acute hyperglycemia and diabetes, the mechanisms underlying these pathological changes remain unclear. Here, we tested the hypothesis that increased Ca(2+) sparklet activity contributes to higher Ca(2+) influx in cerebral artery smooth muscle during acute hyperglycemia and in an animal model of non-insulin-dependent, type 2 diabetes: the dB/dB mouse. Consistent with this hypothesis, acute elevation of extracellular glucose from 10 to 20 mM increased the density of low activity and persistent Ca(2+) sparklet sites as well as the amplitude of LTCC currents in wild-type cerebral arterial myocytes. Furthermore, Ca(2+) sparklet activity and LTCC currents were higher in dB/dB than in control myocytes. We found that activation of PKA contributed to higher Ca(2+) sparklet activity during hyperglycemia and diabetes. In addition, we found that the interaction between PKA and the scaffolding protein A-kinase anchoring protein was critical for the activation of persistent Ca(2+) sparklets by PKA in cerebral arterial myocytes after hyperglycemia. Accordingly, PKA inhibition equalized Ca(2+) sparklet activity between dB/dB and wild-type cells. These findings suggest that hyperglycemia increases Ca(2+) influx by increasing Ca(2+) sparklet activity via a PKA-dependent pathway in cerebral arterial myocytes and contributes to vascular dysfunction during diabetes.

PICK1/calcineurin suppress ASIC1-mediated Ca2+ entry in rat pulmonary arterial smooth muscle cells

“…Although this will decrease [Ca 2ϩ ] i and lead to smooth muscle relaxation, increasing the Ca 2ϩ load of the SR will also lead to faster turn around and increased release of Ca 2ϩ from the stores upon subsequent and/or continuous activation. Indeed, PKA increases Ca 2ϩ -spark frequency mediated by SR ryanodine receptor channels (RyR) (18,30,47). It is possible that PKA not only regulates SR Ca 2ϩ through SERCA and RyR channels but also by activating the store-operated channels responsible for replenishing the SR. PKA has recently been shown to activate the heteromeric Orai1/Orai3 channel through phosphorylation of STIM1 in HEK-293 cells (43).…”

Diabetes-Induced Inhibition of Voltage-Dependent Calcium Channels in the Retinal Microvasculature: Role of Spermine

“…For example, McGinty et al 35 found decreased VDCC activity in pericytes cultured in 25 mM glucose. However, perhaps because hyperglycemia in vitro does not fully mimic diabetes, our study of microvascular complexes did not reveal a significant effect of diabetes on VDCC function in the pericyte-containing capillaries.…”

Elevated Glucose Levels Promote Contractile and Cytoskeletal Gene Expression in Vascular Smooth Muscle via Rho/Protein Kinase C and Actin Polymerization

“…Recent reports suggest that hyperglycemia and diabetes can promote persistent calcium sparklet activity via activation of L-type calcium channels in arterial smooth muscle (70,71). Interestingly, sparklet activity is controlled by PKC and underlies a sustained calcium entry through persistent L-type channel activity (72).…”