Figure 1. Kallikrein related peptidase 6-mediated Ca²⁺ signaling in primary astrocytes is regulated in part by activation of PAR1.

Traces, photomicrographs, and histograms show fluorescence intensity measured in Rhod-3 loaded murine astrocytes at baseline and in response to recombinant Klk6 (150 nM), a PAR1-activating peptide (PAR1-AP, 40 μM), or a PAR2-activating peptide (PAR2-AP, 100 μM), applied alone or sequentially. (A to F) Application of Klk6 or PAR-APs alone elicited a rapid increase in intracellular Ca²⁺ expressed as change in fluorescence intensity (ΔF) over baseline intensity (F₀), expressed as ΔF/F₀ = [(F – F₀)/F₀]. Subsequent application of either PAR1-AP (A to C), or PAR2-AP (D to F), 240 s later resulted in significantly lower ΔF/F₀. Demonstrating that Klk6-elicited Ca²⁺ signaling occurs primarily down stream of PAR1, reductions in ΔF/F₀ were observed when astrocytes were first treated with PAR1-AP prior to application of Klk6 240 s later (B and C). Treatment of astrocytes with PAR2-AP did not significantly alter subsequent Klk6-elicited Ca2+ responses (E and F). These receptor cross desensitization experiments demonstrate that PAR1 plays an important role in Klk6-induced Ca²⁺ signaling in astrocytes. (*P < 0.05, **P < 0.01, *** P < 0.001, Students t-test). Scale bar = 50 μm.