Protease-activated receptor-1-induced calcium signaling in gingival fibroblasts is mediated by sarcoplasmic reticulum calcium release and extracellular calcium influx

Thrombin is a serine protease activated during injury and inflammation. Thrombin and other proteases generated by periodontal pathogens affect the behavior of periodontal cells via activation of protease-activated receptors (PARs). We noted that thrombin and PAR-1 agonist peptide stimulated intracellular calcium levels ([Ca²⁺]_i) of gingival fibroblasts (GF). This increase of [Ca²⁺]_i was inhibited by EGTA and verapamil. U73122 and neomycin inhibited thrombin- and PAR-1-induced [Ca²⁺]_i. Furthermore, 2-APB (75-100 μM, inositol triphosphate [IP₃] receptor antagonist), thapsigargin (1 μM), SKF-96365 (200 μM) and W7 (50 and 100 μM) also suppressed the PAR-1- and thrombin-induced [Ca²⁺]_i. However, H7 (100, 200 μM) and ryanodine showed little effects. Blocking Ca²⁺ efflux from mitochondria by CGP37157 (50, 100 μM) inhibited both thrombin- and PAR-1-induced [Ca²⁺]_i. Thrombin induced the IP3 production of GF within 30-seconds of exposure, which was inhibited by U73122. These results indicate that mitochondrial calcium efflux and calcium-calmodulin pathways are related to thrombin and PAR-1 induced [Ca²⁺]_i in GF. Thrombin-induced [Ca²⁺]_i of GF is mainly due to PAR-1 activation, extracellular calcium influx via L-type calcium channel, PLC activation, then IP₃ binding to IP3 receptor in sarcoplasmic reticulum, which leads to intracellular calcium release and subsequently alters cell membrane capacitative calcium entry.