Retinal ganglion cell survival is enhanced by gabapentin-lactam in vitro:: evidence for involvement of mitochondrial KATP channels

Background. Recently, gabapentin-lactam (GBP-L) was shown to be neuroprotective in vivo. It has been suggested that GBP-L may act by opening mitochondrial ATP-sensitive potassium (K-ATP) channels. We tested this hypothesis by quantifying the effect of GBP-L on the survival of purified retinal ganglion cells (RGCs). Methods. RGCs were purified from early postnatal rat retinae by immunopanning with antibodies against Thy1.1 and cultured in serum-free medium for 2 days. Cell survival was quantified by counting vital cells under phase-contrast optics. Results were normalized to controls. RGCs were treated with various concentrations (3.2-320 muM) of GBP-L with and without 1 muM glibenclamide, blocking both plasmalemmal and mitochondrial K-ATP channels, or 100 muM 5-hydroxydecanoate (5-HD), antagonizing selectively mitochondrial K-ATP channels. For comparison, additional cultures were treated with 32 muM gabapentin, the parent drug of GBP-L. A combination of the neurotrophic factors BDNF and CNTF (50 ng/ml each) served as a positive control. Results. GBP-L increased RGC survival to a maximum of 145+/-5% (mean +/- SEM) in a concentration-dependent manner. The pEC(50) was 5.0, CI95 [4.7, 5.3]. Preincubation with glibenclamide changed the dose-response of GBP-L, indicating that it acted as a competitive antagonist with a pA2 value of 6.8, CI95 [5.9, 7.5]. 5-HD completely blocked the survival-promoting effect of GBP-L. Gabapentin had no effect, whereas the combination of CNTF and BDNF enhanced survival to 177+/-9%. Conclusions. GBP-L, but not gabapentin, can promote the survival of cultured central nervous system neurons, possibly by opening mitochondrial K-ATP channels. These results suggest further testing of GBP-L as a potentially neuroprotective drug.