Mechanism of action of the non-steroidal anti-inflammatory drug flufenamate on [Ca2+]i and Ca(2+)-activated currents in neurons

Gap Junctions Contribute to the Regulation of Walking-Like Activity in the Adult Mudpuppy (Necturus Maculatus)

Although gap junctions are widely expressed in the developing central nervous system, the role of electrical coupling of neurons and glial cells via gap junctions in the spinal cord in adults is largely unknown. We investigated whether gap junctions are expressed in the mature spinal cord of the mudpuppy and tested the effects of applying gap junction blocker on the walking-like activity induced by NMDA or glutamate in an in vitro mudpuppy preparation. We found that glial and neural cells in the mudpuppy spinal cord expressed different types of connexins that include connexin 32 (Cx32), connexin 36 (Cx36), connexin 37 (Cx37), and connexin 43 (Cx43). Application of a battery of gap junction blockers from three different structural classes (carbenexolone, flufenamic acid, and long chain alcohols) substantially and consistently altered the locomotor-like activity in a dose-dependent manner. In contrast, these blockers did not significantly change the amplitude of the dorsal root reflex, indicating that gap junction blockers did not inhibit neuronal excitability nonselectively in the spinal cord. Taken together, these results suggest that gap junctions play a significant modulatory role in the spinal neural networks responsible for the generation of walking-like activity in the adult mudpuppy.

Flufenamic acid prevents behavioral manifestations of salicylate-induced tinnitus in the rat

INTRODUCTION

Tinnitus is defined as a phantom auditory sensation, the perception of sound in the absence of external acoustic stimulation. Given that flufenamic acid (FFA) blocks TRPM2 cation channels, resulting in reduced neuronal excitability, we aimed to investigate whether FFA suppresses the behavioral manifestation of sodium salicylate (SSA)-induced tinnitus in rats.

MATERIAL AND METHODS

Tinnitus was evaluated using a conditioned lick suppression model of behavioral testing. Thirty-one Wistar rats, randomly divided into four treatment groups, were trained and tested in the behavioral experiment: (1) control group: DMSO + saline (n = 6), (2) SSA group: DMSO + SSA (n = 6), (3) FFA group: FFA (66 mg/kg bw) + saline (n = 9), (4) FFA + SSA group: FFA (66 mg/kg bw) + SSA (400 mg/kg bw) (n = 10). Localization of TRPM2 to the plasma membrane of cochlear nucleus neurons was demonstrated by confocal microscopy.

RESULTS

Pavlovian training resulted in strong suppression of licking, having a mean value of 0.05 ±0.03 on extinction day 1, which is below the suppression training criterion level of 0.20 in control tinnitus animals. The suppression rate for rats having both FFA (66 mg/kg bw) and SSA (400 mg/kg bw) injections was significantly lower than that for the rats having SSA injections (p < 0.01).

CONCLUSIONS

We suggest that SSA-induced tinnitus could possibly be prevented by administration of a TRPM2 ion channel antagonist, FFA at 66 mg/kg bw.

Dopamine-induced oscillations of the pyloric pacemaker neuron rely on release of calcium from intracellular stores

Endogenously bursting neurons play central roles in many aspects of nervous system function, ranging from motor control to perception. The properties and bursting patterns generated by these neurons are subject to neuromodulation, which can alter cycle frequency and amplitude by modifying the properties of the neuron's ionic currents. In the stomatogastric ganglion (STG) of the spiny lobster, Panulirus interruptus, the anterior burster (AB) neuron is a conditional oscillator in the presence of dopamine (DA) and other neuromodulators and serves as the pacemaker to drive rhythmic output from the pyloric network. We analyzed the mechanisms by which DA evokes bursting in the AB neuron. Previous work showed that DA-evoked bursting is critically dependent on external calcium (Harris-Warrick RM, Flamm RE. J Neurosci 7: 2113-2128, 1987). Using two-photon microscopy and calcium imaging, we show that DA evokes the release of calcium from intracellular stores well before the emergence of voltage oscillations. When this release from intracellular stores is blocked by antagonists of ryanodine or inositol trisphosphate (IP(3)) receptor channels, DA fails to evoke AB bursting. We further demonstrate that DA enhances the calcium-activated inward current, I(CAN), despite the fact that it significantly reduces voltage-activated calcium currents. This suggests that DA-induced release of calcium from intracellular stores activates I(CAN), which provides a depolarizing ramp current that underlies endogenous bursting in the AB neuron.

Functional distinctions in cytosolic calcium regulation between cells of the glomerular filtration barrier

The importance of intracellular calcium ([Ca(2+)]i) regulation in the glomerular filtration barrier (GFB) has recently been highlighted by mutations in the cation channel TRPC6, resulting in a renal-specific phenotype. We examined the effects of FFA, a tool that can activate TRPC6, on [Ca(2+)]i in human conditionally immortalised glomerular endothelial cells (ciGEnC) and human podocytes (ciPod) that form the GFB. Changes in [Ca(2+)]i stimulated by FFA were measured in Fura 2-AM loaded cells. In GEnC, cell activation by FFA was dependent on external Ca(2+), yet in ciPod it was not. Depletion of internal Ca(2+) stores with thapsigargin did not affect cell activation by FFA in ciGEnC, but inhibited it in ciPod in a nephrin-dependent manner, demonstrated using nephrin deficient (ND) ciPod in conjunction with nephrin rescue experiments. FFA induced [Ca(2+)]i store release in ciPod, but not in ciGEnC or ND ciPod. In parallel, there were differences in the localisation of overexpressed TRPC6 between ciGEnC and ciPod. Furthermore, co-transfection of nephrin with TRPC6 in HEK293 cells reduced the FFA-induced increase in [Ca(2+)]i and nephrin clustering altered TRPC6 distribution. In conclusion, cell activation by FFA in podocytes stimulates the opening of a Ca(2+) channel, probably TRPC6, in a nephrin-dependent manner with a different activation profile to GEnC.

Diacylglycerol analogues activate second messenger-operated calcium channels exhibiting TRPC-like properties in cortical neurons

The lipid diacylglycerol (DAG) analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) was used to verify the existence of DAG-sensitive channels in cortical neurons dissociated from E13 mouse embryos. Calcium imaging experiments showed that OAG increased the cytosolic concentration of Ca(2+) ([Ca(2+)]i) in nearly 35% of the KCl-responsive cells. These Ca(2+) responses disappeared in a Ca(2+)-free medium supplemented with EGTA. Mn(2+) quench experiments showed that OAG activated Ca(2+)-conducting channels that were also permeant to Ba(2+). The OAG-induced Ca(2+) responses were unaffected by nifedipine or omega-conotoxin GVIA (Sigma-Aldrich, Saint-Quentin Fallavier, France) but blocked by 1-[beta-(3-(4-Methoxyphenyl)propoxy)-4-methoxyphenethyl]-1H-imidazole hydrochloride (SKF)-96365 and Gd(3+). Replacing Na(+) ions with N-methyl-D-glucamine diminished the amplitude of the OAG-induced Ca(2+) responses showing that the Ca(2+) entry was mediated via Na(+)-dependent and Na(+)-independent mechanisms. Experiments carried out with the fluorescent Na(+) indicator CoroNa Green showed that OAG elevated [Na(+)]i. Like OAG, the DAG lipase inhibitor RHC80267 increased [Ca(2+)]i but not the protein kinase C activator phorbol 12-myristate 13-acetate. Moreover, the OAG-induced Ca(2+) responses were not regulated by protein kinase C activation or inhibition but they were augmented by flufenamic acid which increases currents through C-type transient receptor potential protein family (TRPC) 6 channels. In addition, application of hyperforin, a specific activator of TRPC6 channels, elevated [Ca(2+)]i. Whole-cell patch-clamp recordings showed that hyperforin activated non-selective cation channels. They were blocked by SKF-96365 but potentiated by flufenamic acid. Altogether, our data show the presence of hyperforin- and OAG-sensitive Ca(2+)-permeable channels displaying TRPC6-like properties. This is the first report revealing the existence of second messenger-operated channels in cortical neurons.

Flufenamic acid affects multiple currents and causes intracellular Ca2+ release in Aplysia bag cell neurons

Flufenamic acid (FFA) is a nonsteroidal antiinflammatory agent, commonly used to block nonselective cation channels. We previously reported that FFA potentiated, rather than inhibited, a cation current in Aplysia bag cell neurons. Prompted by this paradoxical result, the present study examined the effects of FFA on membrane currents and intracellular Ca2+ in cultured bag cell neurons. Under whole cell voltage clamp, FFA evoked either outward (I out) or inward (I in) currents. I out had a rapid onset, was inhibited by the K+ channel blocker, tetraethylammonium, and was associated with both an increase in membrane conductance and a negative shift in the whole cell current reversal potential. I in developed more slowly, was inhibited by the cation channel blocker, Gd3+, and was concomitant with both an increased conductance and positive shift in reversal potential. FFA also enhanced the use-dependent inactivation and caused a positive-shift in the activation curve of the voltage-dependent Ca2+ current. Furthermore, as measured by ratiometric imaging, FFA produced a rise in intracellular Ca2+ that persisted in the absence of extracellular Ca2+ and was reduced by depleting either the endoplasmic reticulum and/or mitochondrial stores. Ca2+ appeared to be involved in the activation of I in, as strong intracellular Ca2+ buffering effectively eliminated I in but did not alter I out. Finally, the effects of FFA were likely not due to block of cyclooxygenase given that the general cyclooxygenase inhibitor, indomethacin, failed to evoke either current. That FFA influences a number of neuronal properties needs to be taken into consideration when employing it as a cation channel antagonist.

New molecular mechanisms on the activation of TRPM2 channels by oxidative stress and ADP-ribose

The Na(+) and Ca(2+)-permeable melastatin related transient receptor potential (TRPM2) cation channels can be gated either by ADP-ribose (ADPR) in concert with Ca(2+) or by hydrogen peroxide (H(2)O(2)), an experimental model for oxidative stress, and binding to the channel's enzymatic Nudix domain. Since the mechanisms that lead to TRPM2 inhibiting in response to ADPR and H(2)O(2) are not understood, I reviewed the effects of various inhibitors such as flufenamic acid and PARP inhibitors on ADPR, NAD(+) and H(2)O(2)-induced TRPM2 currents. In our experimental study, TRPM2 cation channels in chinese hamster ovary transected cells were gated both by ADPR and NAD(+). In addition, H(2)O(2) seems to activate TRPM2 by changing to the hydroxyl radical in the intracellular space after passing the plasma membrane. Experimental studies with respect to patch-clamp and Ca(2+) imaging, inhibitor roles of antioxidants are also summarized in the review.

Apamin-sensitive calcium-activated potassium currents (SK) are activated by persistent calcium currents in rat motoneurons

Low voltage-activated persistent inward calcium currents (Ca PICs) occur in rat motoneurons and are mediated by Cav1.3 L-type calcium channels (L-Ca current). The objectives of this paper were to determine whether this L-Ca current activates a sustained calcium-activated potassium current (SK current) and examine how such SK currents change with spinal injury. For comparison, the SK current that produces the postspike afterhyperpolarization (mAHP) was also quantified. Intracellular recordings were made from motoneurons of adult acute and chronic spinal rats while the whole sacrocaudal spinal cord was maintained in vitro. Spikes/AHPs were evoked with current injection or ventral root stimulation. Application of the SK channel blocker apamin completely eliminated the mAHP, which was not significantly different in chronic and acute spinal rats. The Ca PICs were measured with slow voltage ramps (or steps) with TTX to block sodium currents. In chronic spinal rats, the PICs were activated at -58.6 +/- 6.0 mV and were 2.2 +/- 1.2 nA in amplitude, significantly larger than in acute spinal rats. Apamin significantly increased the PIC, indicating that there was an SK current activated by L-Ca currents (SK(L) current), which ultimately reduced the net PIC. This SK(L) current was not different in acute and chronic spinal rats. The SK(AHP) and the SK(L) currents were activated by different calcium currents because the mAHP/SK(AHP) was blocked by the N, P-type calcium channel blocker omega-conotoxin MVIIC and was resistant to the L-type calcium channel blocker nimodipine, whereas the L-Ca and SK(L) currents were blocked by nimodipine. Furthermore, the SK(AHP) current activated within 10 ms of the spike, whereas the SK(L) current was delayed approximately 100 ms after the onset of the L-Ca current, suggesting that the SK(L) currents were not as spatially close to the L-Ca currents. Finally, the SK(L) and the L-Ca currents were poorly space clamped, with oscillations at their onset and hysteresis in their activation and deactivation voltages, consistent with currents of dendritic origin. The impact of these dendritic currents was especially pronounced in 15% of motoneurons, where apamin led to uncontrollable L-Ca currents that could not be deactivated, even with large hyperpolarizations of the soma. Thus, although the SK(L) currents are fairly small, they play a critical role in terminating the dendritic L-Ca currents.

Niflumic acid inhibits chloride conductance of rat skeletal muscle by directly inhibiting the CLC-1 channel and by increasing intracellular calcium

BACKGROUND AND PURPOSE

Given the crucial role of the skeletal muscle chloride conductance (gCl), supported by the voltage-gated chloride channel CLC-1, in controlling muscle excitability, the availability of ligands modulating CLC-1 are of potential medical as well as toxicological importance. Here, we focused our attention on niflumic acid (NFA), a molecule belonging to the fenamates group of non-steroidal anti-inflammatory drugs (NSAID).

EXPERIMENTAL APPROACH

Rat muscle Cl(-) conductance (gCl) and heterologously expressed CLC-1 currents were evaluated by means of current-clamp (using two-microelectrodes) and patch-clamp techniques, respectively. Fura-2 fluorescence was used to determine intracellular calcium concentration, [Ca(2+)](i), in native muscle fibres.

KEY RESULTS

NFA inhibited native gCl with an IC(50) of 42 muM and blocked CLC-1 by interacting with an intracellular binding site. Additionally, NFA increased basal [Ca(2+)](i) in myofibres by promoting a mitochondrial calcium efflux that was not dependent on cyclooxygenase or CLC-1. A structure-activity study revealed that the molecular conditions that mediate the two effects are different. Pretreatment with the Ca-dependent protein kinase C (PKC) inhibitor chelerythrine partially inhibited the NFA effect. Therefore, in addition to direct channel block, NFA also inhibits gCl indirectly by promoting PKC activation.

CONCLUSIONS AND IMPLICATIONS

These cellular effects of NFA on skeletal muscle demonstrate that it is possible to modify CLC-1 and consequently gCl directly by interacting with channel proteins and indirectly by interfering with the calcium-dependent regulation of the channel. The effect of NFA on mitochondrial calcium stores suggests that NSAIDs, widely used drugs, could have potentially dangerous side-effects.

Effects of flufenamic acid on fictive locomotion, plateau potentials, calcium channels and NMDA receptors in the lamprey spinal cord

A Ca(2+)-activated, non-selective cation current (I(CAN)) has been suggested to contribute to plateau potentials in lamprey reticulospinal neurons, providing the drive for locomotor initiation. Flufenamic acid (FFA) is commonly used as a blocker of I(CAN). To explore the effects of FFA on spinal locomotor pattern generation, we induced fictive locomotion in the isolated lamprey spinal cord. Bath-applied FFA (100-200microM) caused a marked reduction of amplitude and regularity of the locomotor burst activity. We next analyzed the NMDA-induced membrane potential oscillations in single spinal neurons. The duration of depolarizing plateaus was markedly reduced when applying FFA, suggesting an involvement of I(CAN). However, in experiments with intracellular injection of the Ca(2+) chelator BAPTA, and in the presence of the K(Ca)-channel blocker apamin, no support was found for an involvement of I(CAN). We therefore explored alternative explanations of the effects of FFA. FFA reduced the size of the slow, Ca(2+)-dependent afterhyperpolarization, suggesting an influence on calcium channels. FFA also reduced the NMDA component of reticulospinal EPSPs as well as NMDA-induced depolarizing responses, demonstrating an influence on NMDA receptors. These non-selective effects of FFA can account for its influence on fictive locomotion and on membrane potential oscillations and thus, a specific involvement of the I(CAN) current in the lamprey spinal cord is not supported.

Bistable Behavior Originating in the Axon of a Crustacean Motor Neuron

Both vertebrate and invertebrate motor neurons can display bistable behavior in which self-sustained tonic firing results from a brief excitatory stimulus. Induction of the bistability is usually dependent on activation of intrinsic conductances located in the somatodendritic area and is commonly sensitive to action of neuromodulators. We have observed bistable behavior in a neuromuscular preparation from the foregut of the crab Cancer borealis that consists of the gastric mill 4 (gm4) muscle and the nerve that innervates it, the dorsal gastric nerve ( dgn). Nerve-evoked contractions of enhanced amplitude and long duration (>30 s) were induced by extracellular stimulation when the stimulus voltage was above a certain threshold. Intracellular and extracellular recordings showed that the large contractions were accompanied by persistent firing of the dorsal gastric (DG) motor neuron that innervates gm4. The persistent firing could be induced only by stimulating a specific region of the axon and could not be triggered by depolarizing the soma, even at current amplitudes that induced high-frequency firing of the neuron. The bistable behavior was abolished in low-Ca2+saline or when nicardipine or flufenamic acid, blockers of L-type Ca2+and Ca2+-activated nonselective cation currents, respectively, was applied to the axonal stimulation region of the dgn. Negative immunostaining for synapsin and synaptotagmin argued against the presence of synaptic/modulatory neuropil in the dgn. Collectively, our results suggest that bistable behavior in a motor neuron can originate in the axon and may not require the action of a locally released neuromodulator.

TRPM2: a calcium influx pathway regulated by oxidative stress and the novel second messenger ADP-ribose

A unique functional property within the transient receptor potential (TRP) family of cation channels is the gating of TRP (melastatin) 2 (TRPM2) channels by ADP-ribose (ADPR). ADPR binds to the intracellular C-terminal tail of TRPM2, a domain that shows homology to enzymes with pyrophosphatase activity. Cytosolic Ca(2+) enhances TRPM2 gating by ADPR; ADPR and Ca(2+) in concert may be an important messenger system mediating Ca(2+) influx. Other stimuli of TRPM2 include NAD and H(2)O(2) and cyclic ADPR, which may act synergistically with ADPR. H(2)O(2), an experimental paradigm of oxidative stress, may also induce the formation of ADPR in the nucleus or mitochondria. In this review, we summarize the gating properties of TRPM2 and the proposed pathways of channel activation in vivo. TRPM2 is likely to be a key player in several signalling pathways, mediating cell death in response to oxidative stress or in reperfusion injury. Moreover, it plays a decisive role in experimentally induced diabetes mellitus and in the activation of leukocytes.

Flufenamic acid is a pH-dependent antagonist of TRPM2 channels

Like a number of other TRP channels, TRPM2 is a Ca(2+)-permeable non-selective cation channel, the activity of which is regulated by intracellular and extracellular Ca(2+). A unique feature of TRPM2 is its activation by ADP-ribose and chemical species that arise during oxidative stress, for example, NAD(+) and H(2)O(2). These properties have lead to proposals that this channel may play a role in the cell death produced by pathological redox states. The lack of known antagonists of this channel have made these hypotheses difficult to test. Here, we demonstrate, using patch clamp electrophysiology, that the non-steroidal anti-inflammatory compound flufenamic acid (FFA) inhibits recombinant human TRPM2 (hTRPM2) as well as currents activated by intracellular ADP-ribose in the CRI-G1 rat insulinoma cell line. All concentrations tested in a range from 50 to 1000 microM produced complete inhibition of the TRPM2-mediated current. Following FFA removal, a small (typically 10-15%) component of current was rapidly recovered (time constant approximately 3 s), considerably longer periods in the absence of FFA produced no further current recovery. Reapplication of FFA re-antagonised the recovered current and subsequent FFA washout produced recovery of only a small percentage of the reblocked current. Decreasing extracellular pH accelerated FFA inhibition of TRPM2. Additional experiments indicated hTRPM2 activation was required for FFA antagonism to occur and that the generation of irreversible antagonism was preceded by a reversible component of block. FFA inhibition could not be induced by intracellular application of FFA. ADP-ribose activated currents in the rat insulinoma cell line CRI-G1 were also antagonised by FFA with concentration- and pH-dependent kinetics. In contrast to the observations made with hTRPM2, antagonism of ADP-ribose activated currents in CRI-G1 cells could be fully reversed following FFA removal. These experiments suggest that FFA may be a useful tool antagonist for studies of TRPM2 function.

Fulfenamic acid sensitive, Ca(2+)-dependent inward current induced by nicotinic acetylcholine receptors in dopamine neurons

Nicotinic acetylcholine receptors (nAChRs) exhibit high Ca(2+) permeabilities and the Ca(2+)-influx through the nAChRs may be involved in regulation of a variety of signal processing in the postsynaptic neurons. The mesencephalic dopamine (DA) neurons receive cholinergic inputs from the brainstem and express abundant nAChRs. Here we report that the Ca(2+)-influx induced by a transient pressure application of ACh activates an inward current mediated by nAChRs and subsequently an inward current component that is sensitive to fulfenamic acid (FFA) and phenytoin, presumably a Ca(2+)-activated nonselective cation current in the DA neurons in the midbrain slices of the rat. The FFA- and phenytoin-sensitive current exhibits a negative slope conductance below -40 mV, suggesting its role in significant enhancement of depolarizing responses. In the current clamp recordings with perforated patch clamp configuration, bath application of carbachol markedly enhanced the glutamate-induced depolarization, which led to a long-lasting depolarizing hump. Activation of nAChRs is involved in this process, in cooperation with muscarinic receptors that suppress afterhyperpolarization caused by Ca(2+)-activated K(+)-channels. The long-lasting depolarizing hump was suppressed by FFA. All these results suggested a potential role of the FFA-sensitive current triggered by nAChR activation in marked enhancement of the excitatory synaptic response in DA neurons.

Calcium-activated cationic channel in rat sensory neurons

Ion channels in sensory neurons are molecular sensors that detect external stimuli and transduce them to neuronal signals. Although Ca2+-activated nonselective cation (CAN) channels were found in many cell types, CAN channels in mammalian sensory neurons are not yet identified. In the present study, we describe an ion channel that is activated by intracellular Ca2+ in cultured rat sensory neurons. Half-maximal concentration of Ca2+ in activating the CAN channel was approximately 780 micro m. The current-voltage relationship of this channel was linear with a unit conductance of 28.8 +/- 0.4 pS at -60 mV in symmetrical 140 mm Na+ solution. The CAN channel was permeable to monovalent cations such as Na+, K+, Cs+, and Li+, but poorly permeable to Ca2+. The CAN channel in mammalian sensory neurons was reversibly blocked by intracellular adenine nucleotides, such as ATP, ADP, and AMP. Interestingly, single-channel currents activated by Ca2+ were blocked by fenamates, such as flufenamic acid, a class of nonsteroidal anti-inflammatory drugs. Thus, these results suggest that CAN channels in mammalian sensory neurons would participate in modulating nociceptive neural transmission in response to ever-changing intracellular Ca2+ in the local microenvironment.

A cellular mechanism for the transformation of a sensory input into a motor command

The initiation and control of locomotion largely depend on processing of sensory inputs. The cellular bases of locomotion have been extensively studied in lampreys where reticulospinal (RS) neurons constitute the main descending system activating and controlling the spinal locomotor networks. Ca(2+) imaging and intracellular recordings were used to study the pattern of activation of RS neurons in response to cutaneous stimulation. Pressure applied to the skin evoked a linear input/output relationship in RS neurons until a threshold level, at which a depolarizing plateau was induced, the occurrence of which was associated with the onset of swimming activity in a semi-intact preparation. The occurrence of a depolarizing plateau was abolished by blocking the NMDA receptors that are located on RS cells. Moreover, the depolarizing plateaus were accompanied by a rise in [Ca(2+)](i), and an intracellular injection of the Ca(2+) chelator BAPTA into single RS cells abolished the plateaus, suggesting that the latter are Ca(2+) dependent and rely on intrinsic properties of RS cells. The plateaus were shown to result from the activation of a Ca(2+)-activated nonselective cation current that maintains the cell in a depolarized state. It is concluded that this intrinsic property of the RS neuron is then responsible for the transformation of an incoming sensory signal into a motor command that is then forwarded to the spinal locomotor networks.

Block of hippocampal CAN channels by flufenamate

Ca(2+)-activated non-selective cation (CAN) channels are activated by cytoplasmic Ca(2+) and I(CAN) underlies many slow depolarizing processes in neurons including a putative role in excitotoxicity. CAN channels in many non-neuronal cells are blocked by non-steroidal antiinflammatory drugs that are derivatives of diphenylamine-2-carboxylate (DPC). The DPC derivative flufenamate (FFA) has a complex effect on certain neurons, whereby it blocks CAN channels and increases [Ca(2+)](i). We report here that FFA, but not the parent compound, DPC, blocks CAN channels in hippocampal CA1 neurons. As was the case in other neurons, the effects of FFA are complex and include a maintained rise in [Ca(2+)](i). Furthermore, the CAN channel blocking ability of FFA persists even when the channels have been potentiated by a Ca(2+)-dependent process. The use of a CAN channel-blocking drug is important for delineating CAN channel-dependent processes and may provide a basis for therapy for CAN channel-dependent events in ischemia.