Calmodulin Regulates Calcium Sparklet Activity in Vascular Smooth Muscle

Abstract

Calcium influx through L-type calcium channels (LTCCs) influences numerous physiological processes in excitable cells ranging from contraction, memory and gene expression. Clusters of LTCCs can operate in a PKCalpha-dependent, high open probability mode that generates sites of sustained calcium influx called “persistent calcium sparklets”. In vascular smooth muscle, persistent calcium sparklets contribute to local and global calcium. Calcium sparklets activity varies regionally within smooth muscle cells. At present however, the mechanisms underlying heterogeneous sparklet activity are incompletely understood. Here, we use TIRF microscopy and whole-cell patch clamp electrophysiology to investigate the role calmodulin in the modulation of calcium sparklet activity. We found that inhibition of calmodulin increases calcium sparklet activity in wild type (WT) smooth muscle cells. Inhibition of calmodulin in PKCalpha KO cells, which are devoid of persistent calcium sparklets, increased calcium influx by evoking new persistent calcium sparklet sites and by increasing the activity of previously low activity sites in these cells. On the basis of these finding, we hypothesize that calmodulin plays a critical role in determining the activity of calcium sparklet sites in arterial smooth muscle. This work was supported by the National Institutes of Health and the American Heart Association.