ABSTRACT
Changes in intracellular Ca2þ concentration play fundamental roles in the regulation of contraction and relaxation of smooth muscle cells (SMCs). The Ca2þ required for the activation of contractile apparatus is supplied by the influx from extracellular space through Ca2þ-permeable channels in the plasma membrane and=or by the release from storage sites, mainly the sarcoplasmic reticulum (SR), through Ca2þ releasing channels. Two families of Ca2þ-releasing channels are present in Ca2þ storage sites in SMCs: ryanodine receptors (RyRs) and inositol trisphosphate receptors (IP3Rs). This chapter provides a general overview of Ca2þ-releasing channels: their structure, regulation, and expression in SMCs and specific information about them in pulmonary vascular SMCs (PVSMCs). Furthermore, the regulation of ion channel activity in the plasma membrane by local Ca2þ transients following the activation of RyRs and IP3Rs in SMCs (1,2) will be discussed. Additional reviews about local Ca2þ transients in the pulmonary artery are available in Chapter 25.
