We have originated a family of N,N'-disubstituted
guanidines that block the voltage-activated Ca2+ and Na+ channels governing
glutamate release. These compounds,
CNS 1237 (N-acenaphthyl-N'-methoxynaphthyl
guanidine) and its analogues, are "use dependent" in their ability to attenaute
neurotransmitter release: they block
glutamate release with greater efficacy under conditions of persistent or repetitive depolarization, as would be encountered under pathophysiological circumstances, relative to their ability to block
glutamate release elicited by brief, transient depolarizations more characteristic of normal physiological release events in nonischemic brain. Using electrophysiological and rapid kinetic methods, we have differentiated the use-dependent block of the relevant Na+ and Ca2+ channels governing
neurotransmitter release from the mechanism of channel antagonism exhibited by, respectively, the substituted
guanidine Na+ channel blocker
tetrodotoxin (TTX) and
venom peptide Ca2+ antagonists. To characterize use-dependent Na+ channel block by
CNS 1237, we have employed whole-cell voltage-clamp recordings from a Chinese hamster ovary (CHO) cell line expressing cloned mammalian type II Na+ channels. These experiments demonstrated that, in contrast to the actions of TTX under the same conditions, the potency of Na+ channel block by
CNS 1237 is greatly enhanced by depolarizing stimuli in a frequency-dependent manner. Ca2+ channel-activated
glutamate release from brain nerve terminal preparations was measured with approximately 300 msec time resolution over a 5-second period of high K(+)-depolarization, using a rapid superfusion technique.
CNS 1237 and analogues, at 1-3 microM, accelerated the decay of
glutamate release by 40-70%, reflecting depolarization-induced enhancement of block. In contrast, blockade of
glutamate release by the Ca2+ channel antagonist
peptide toxins omega-aga IV-A (from
spider venom) and
omega-conotoxin M-VII-C (from cone
snail venom) exhibited "reverse-use-dependence:" at concentrations of 0.3 microM, which blocked the initial amplitude of
glutamate release by 40-60%, the decay time constant for
glutamate release was significantly increased, indicating depolarization-induced relief of block. These findings establish that
CNS 1237 and other members of this compound series are use-dependent blockers of the voltage-activated
ion channels governing
glutamate release. Studies of
CNS 1237 in the rat
middle cerebral artery occlusion (MCAO) focal
stroke model have indicated
infarct size reduction comparable to that observed by the same investigators for the
glutamate release blocker (
BW 619C89 (Burroughs-Wellcome, now in clinical development). Maximal
infarct size reduction is achieved with a 3-mg/kg bolus followed by a 4-hour infusion of 0.75 mg/kg/hr.(ABSTRACT TRUNCATED AT 400 WORDS)