Calcium Mobilization and Spontaneous Transient Outward Current Characteristics upon Agonist Activation of P2Y2 Receptors in Smooth Muscle Cells

Abstract

A quantitative model is provided that links the process of metabotropic receptor activation and sequestration to the generation of inositol 1,4,5-trisphosphate, the subsequent release of calcium from the central sarcoplasmic reticulum, and the consequent release of calcium from subsarcolemma sarcoplasmic reticulum that acts on large-conductance potassium channels to generate spontaneous transient outward currents (STOCs). This model is applied to the case of STOC generation in vascular A7r5 smooth muscle cells that have been transfected with a chimera of the P2Y(2) metabotropic receptor and green fluorescent protein (P2Y(2)-GFP) and exposed to the P2Y(2) receptor agonist uridine 5'-triphosphate. The extent of P2Y(2)-GFP sequestration from the membrane on exposure to uridine 5'-triphosphate, the ensuing changes in cytosolic calcium concentration, as well as the interval between STOCs that are subsequently generated, are used to determine parameter values in the model. With these values, the model gives a good quantitative prediction of the dynamic changes in STOC amplitude observed upon activation of metabotropic P2Y(2) receptors in the vascular smooth muscle cell line.

A Ca2+‐dependent chloride current and Ca2+ influx via Cav1.2 ion channels play major roles in P2Y receptor‐mediated pulmonary vasoconstriction

“…We showed that both agonists act via two P2Y subtypes to evoke contraction in this tissue, most likely P2Y 6 , plus P2Y 2 or P2Y 4 receptors (Chootip et al ., 2002; 2005; Kennedy et al ., 2010). P2Y 2 (Sromek and Harden, 1998; Flores et al ., 2005; Lemon et al ., 2005) and P2Y 4 (Brinson and Harden, 2001) receptors both desensitize rapidly and with a time‐course compatible with the decay seen in the present study, whereas the P2Y 6 receptor desensitizes much more slowly, reaching a steady‐state over 3–6 h (Robaye et al ., 1997; Brinson and Harden, 2001). Thus, the activation of P2Y 6 and P2Y 2 /P2Y 4 receptors could together lead to the peak contraction, with the subsequent decay reflecting desensitization of P2Y 2 /P2Y 4 receptors, to leave P2Y 6 receptors dominating the plateau.…”

A Kinetic Model for Calcium Dynamics in RAW 264.7 Cells: 1. Mechanisms, Parameters, and Subpopulational Variability

“…Calcium levels can vary substantially from one cell type to another. For example, in excitable cells such as neuronal cells and muscle cells, for which most calcium models and measurement techniques have been developed (13,21,(24)(25)(26)(27)(28), basal [Ca 21 ] i is in the 0.2-0.5 mM range, whereas in nonexcitable cells such as macrophages, including RAW 264.7 cells (29,30), it is between 0.03 and 0.1 mM. In macrophages, due to their nonexcitable nature, oscillations are generally not observed, as evidenced by the Alliance for Cellular Signaling (AfCS) calcium data (29) and discussed in (30)(31)(32).…”

A Mathematical Analysis of Agonist- and KCl-Induced Ca2+ Oscillations in Mouse Airway Smooth Muscle Cells

“…SMCs of various types have been studied extensively. A number of models describing various physiological features of SMC related to cellular Ca 2þ dynamics have been presented in the literature (35)(36)(37)(38)(39). These models, although relevant to their respective cell types, are not directly applicable to ASMCs due to differences in physiological structure and function.…”