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 Ba2+, individually afforded limited protection in 5.6 mM K+. However, survival in 5.6 mM K+ with a combination of 4-AP, TEA and Ba2+ 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.
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