Inhibition of voltage‐gated Ca2+ channels by sst4 stimulation is mediated by Gβγ and PKC activation

Abstract

Healthcare System, Los Angeles, CA Stimulation of somatostatin subtype‐4 receptors (sst4) in isolated retinal ganglion cells (RGCs) inhibits Ca2+ channel current (ICa). Reducing intracellular Ca2+ is known to be neuroprotective; thus, stimulating sst4 may prevent RGC loss in trauma and disease. The aim of this study was to determine the signaling pathways involved in sst4 stimulation leading to suppression of ICa in RGCs. Isolated RGCs were prepared using a modified Thy‐1 immunopanning procedure. Electrophysiology experiments were performed using whole‐cell patch clamp to isolate ICa. L‐803,087 (sst4 agonist, L‐803) inhibited ICa by 40.4% and reduced calcium conductance (2.1 vs. 1.4 nS; p<0.05). Pretreatment of cells with pertussis toxin did not prevent the action of L‐803 (34.7%). Pre‐pulse facilitation did not reverse the inhibitory effects of L‐803 on ICa (11.4 vs. 9.7 %). However, pharmacologic inhibition of Gβγ prevented ICa suppression by L‐803 (23.0%, p<0.05). Inhibition of PKC (GF109203X; GFX) showed a concentration‐dependent effect in preventing the action of L‐803 on ICa (1 μM GFX, 34.3%; 5 μM GFX, 18.4%, p<0.05). This suggests that sst4 stimulation modulates RGC Ca2+ channels via Gβγ and PKC activation. Thus, modulating these signaling pathways may provide unique therapeutic targets to reduce intracellular Ca2+ levels in RGCs. Support from CIHR‐NSHRF RPP, NIH.