Survival of Swiss-Webster mouse cerebellar granule neurons is promoted by a combination of potassium channel blockers

Abstract

Cultured cerebellar granule neurons (CGN) are commonly used to assess neurotoxicity, but are routinely maintained in supraphysiological (25 mM) extracellular K + concentrations [K +] o. We investigated the effect of potassium channel blockade on survival of CGN derived from Swiss-Webster mice in supraphysiological (25 mM) and physiological (5.6 mM) [K +] o. CGN were cultured for 5 days in 25 mM K +, then in 5.6 mM K + or 25 mM K + (control). Viability, assayed 24 h later by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) reduction and by lactate dehydrogenase (LDH) release, was ∼50% in 5.6 mM K + versus 25 mM K + ( p < .001). Potassium channel blockers, 2 mM 4-aminopyridine (4-AP), 2 mM tetraethylammonium (TEA) or 1 mM Ba 2+, individually afforded limited protection in 5.6 mM K +. However, survival in 5.6 mM K + with a combination of 4-AP, TEA and Ba 2+ was similar to survival in 25 mM K + without blockers ( p < .001 versus 5.6 mM K + alone). CGN survival in 25 mM K + was attenuated 25% by 2 μM nifedipine ( p > .001), but nifedipine did not attenuate neuroprotection by K + channel blockers. Together, these results suggest that the survival of CGN depends on the K + permeability of the membrane rather than the activity of a particular type of K + channel, and that the mechanism of neuroprotection by K + channel blockers is different from that of elevated [K +] o.