Role of Protease Activated Receptors in the Intracellular Calcium Dynamics of Neurons and Satellite Cells in the Rat Superior Cervical Ganglia

Abstract

Protease-activated receptors (PARs) mediate cellular responses to various proteases in numerous cell types, including nerve cells. The issue of whether stimulation of PARs induces responses in neurons and satellite cells of sympathetic superior cervical ganglia (SCG) of rats was examined with special reference to PAR mRNA levels and to intracellular Ca²⁺ ([Ca²⁺]_i) changes, since [Ca²⁺]_i is a key factor in intracellular signaling. SCG whose essential structural integrity was maintained intact were used. RT-PCR showed that SCG expressed mRNAs encoding PAR1, 2 and 3, and PAR2 expression was the highest. Confocal microscopic analysis indicated that thrombin and trypsin induced an increase in [Ca²⁺]_i in some neurons and many satellite cells. These proteases initially elicited a [Ca²⁺]_i increase in satellite cells and a subsequent [Ca²⁺]_i change in neurons. Synchronized [Ca²⁺]_i changes in satellite cells were often observed. Neither the removal of extracellular Ca²⁺ nor Ca²⁺ channel blockers affected the trypsin-induced or PAR2-activating peptide (PAR2-AP)-induced [Ca²⁺]_i changes in satellite cells, thus suggesting that these changes were caused by Ca²⁺ mobilization from an internal store, but not by Ca²⁺ influx. However, neither the phospholipase C inhibitor, U73122, nor the IP₃ receptor antagonist, heparin, could inhibit the [Ca²⁺]_i changes of satellite cells, whereas these reagents considerably inhibited the [Ca²⁺]_i changes of neurons. These findings demonstrate the presence of PARs in sympathetic nervous tissue, and establish that proteases induce [Ca²⁺]_i changes in both neurons and satellite cells via Ca²⁺ mobilization.