Ion Channels and Their Regulation in Vascular Smooth Muscle

Vascular smooth muscle excitability is exquisitely regulated by different ion channels that control membrane potential (Em) and the magnitude of intracellular calcium inside the cell to induce muscle relaxation or contraction, which significantly influences the microcirculation. Among them, various members of the K+ channel family, voltage-gated Ca2+ channels, and transient receptor potential (TRP) channels are fundamental for control of vascular smooth muscle excitability. These ion channels exist in complex with numerous signaling molecules and binding partners that modulate their function and, in doing so, impact vascular smooth muscle excitability. In this book chapter, we will review our current understanding of some of these ion channels and binding partners in vascular smooth muscle and discuss how their regulation is critical for proper control of (micro)vascular function

Dynamic L-type CaV1.2 channel trafficking facilitates CaV1.2 clustering and cooperative gating.

L-type CaV1.2 channels are key regulators of gene expression, cell excitability and muscle contraction. CaV1.2 channels organize in clusters throughout the plasma membrane. This channel organization has been suggested to contribute to the concerted activation of adjacent CaV1.2 channels (e.g. cooperative gating). Here, we tested the hypothesis that dynamic intracellular and perimembrane trafficking of CaV1.2 channels is critical for formation and dissolution of functional channel clusters mediating cooperative gating. We found that CaV1.2 moves in vesicular structures of circular and tubular shape with diverse intracellular and submembrane trafficking patterns. Both microtubules and actin filaments are required for dynamic movement of CaV1.2 vesicles. These vesicles undergo constitutive homotypic fusion and fission events that sustain CaV1.2 clustering, channel activity and cooperative gating. Our study suggests that CaV1.2 clusters and activity can be modulated by diverse and unique intracellular and perimembrane vesicular dynamics to fine-tune Ca2+ signals

Total Internal Reflection Fluorescence Microscopy in Vascular Smooth Muscle

This chapter provides an overview of the basic concepts behind Total Internal Reflection Fluorescence Microscopy (TIRFM), and its application to the study of the function and regulation of plasmalemmal Ca2+-permeable channels in vascular smooth muscle. TIRFM utilizes an evanescent wave to selectively excite fluorophores in regions of a sample directly adjacent to the glass coverslip-buffer interface. The principles at the heart of TIRFM are based on the laws of refraction of light and properties of the refractive media. TIRFM relies on the ability to introduce light at angles exceeding a critical angle. A particular innovative use of TIRFM has been on the recording of Ca2+ signals produced by the opening of Ca2+-permeable channels at the plasma membrane of a cell, including vascular smooth muscle cells. The quality of vascular smooth muscle cells is critical for successful recording of sparklets using TIRFM. Single vascular smooth muscle cells can be obtained by enzymatic digestion of freshly dissected arteries from different vascular beds