Diclofenac, a nonsteroidal anti-inflammatory drug (NSAID), has been widely investigated in terms of its pharmacological action, but less is known about its direct effect on ion channels. Here, the effect of diclofenac on voltage-dependent transient outward KC currents (IA) in cultured rat cerebellar granule cells was investigated using the whole-cell voltage-clamp technique. At concentrations of 10 5e10 3 M, diclofenac reversibly increased the IA amplitude in a dose-dependent manner and significantly modulated the steady-state inactivation properties of the IA channels, but did not alter the steady-state activation properties. Furthermore,diclofenac treatment resulted in a slightly accelerated recovery from IA channel inactivation.Intracellular application of diclofenac could mimic the effects induced by extracellular application, although once the intracellular response reached a plateau, extracellular application of diclofenac could induce further increases in the current. These observations indicate that diclofenac might exert its effects on the channel protein at both the inner and outer sides of the cell membrane. Our data provide the first evidence that diclofenac is able to activate transient outward potassium channels in neurons. Although further work will be necessary to define the exact mechanism of diclofenac-induced IA channel activation, this study provides evidence that the nonsteroidal anti-inflammatory drug, diclofenac, may play a novel neuronal role that is worthy of future study.

The inhibitory effect of the melatonin receptor antagonist luzindole on voltage-activated transient outward K current (I) was K(A) investigated in cultured rat cerebellar granule cells using the whole cell voltage-clamp technique. At the concentration of 1 mM to 1 mM,luzindole reversibly inhibited I in a concentration-dependent manner. In addition to reducing the current amplitude of I,luzindole K(A) K(A) accelerated the fast inactivation of I channels and shifted the curves of voltage-dependent steady-state activation and inactivation of K(A) I by 16.6 mV and 27.0 mV, respectively. The inhibitory effect of luzindole was neither use-dependent nor voltage-dependent, K(A) suggesting that the binding affinity of luzindole to I channels is state-dependent. Including luzindole in the pipette solution, or K(A) extracellular application of 4 P-PDOT, an antagonist of melatonin receptors, did not change the luzindole-induced inhibitory effect on the I current, indicating that luzindole exerts its channel blocking inhibitory action at the extracellular mouth of the channel, and that the K(A)effect is not due to action of the melatonin receptors. Our data are the first demonstration that luzindole is able to block transient outward 1 K channels in rat cerebellar granule cells in a state-dependent manner, likely associated with extracellular interaction of the drug with the I inactivation gate.

The effects of 4-aminopyridine (4-AP), a specific blocker of outward K current, on voltage-activated transient outward K current 1(I) and inward Na current (I) were investigated on cultured rat cerebellar granule cells using the whole cell voltage-clamp K(A) Na 1technique. At the concentration of 1–5 mM, 4-AP inhibited both I and I. It reduced the amplitude of peak Na current without K(A) Na significant alteration of the steady-state activation and inactivation properties. The inhibitory effect was not enhanced by repeated 1depolarizing pulses (0.5 or 0.1 Hz), suggesting that the binding affinity of 4-AP on Na channels is state-independent. In contrast, the 1 effect of 4-AP on Na channels appeared to be voltage-dependent, the weaker inhibition occurred at more depolarization. Moreover, 4-AP 1 slowed both the activation and inactivation kinetics of Na current. These effects were similar to those induced by a-scorpion toxin and 1 sea anemone toxins on Na channels in other cell model. Our data demonstrate for the first time that 4-AP is able to block not only 11 1 A-type K channels, but also Na channels in rat cerebellar granule cells. It is concluded that the inhibition exerted by 4-AP on Na current likely differs from that provoked by local anesthetics. The possibility that the binding site of neurotoxin receptor 3 may be involved is discussed.

Our previous study revealed that 4-aminopyridine (4-AP), a specific blocker of A-type current, could also inhibit inward Na+ currents (INa) with a state-independent mechanism in rat cerebellar granule cells. In the present study, we report an inhibitory effect of 4-AP on voltage-gated and tetrodotoxin (TTX)-sensitive INa recorded from cultured rat myoblasts. 4-AP inhibited INa amplitude in a dose-dependent manner between the concentrations of 0.5 and 10 mM without significant alteration in the activation or inactivation kinetics of the channel. By comparison to the 4-AP-induced inhibitory effect on cerebellum neurons, the inhibitory effect on myoblasts was enhanced through repetitive pulse and inflected by changing frequency. Specifically, the lower the frequency of pulse, the higher the inhibition observed, suggesting that block manner is inversely use-dependent. Moreover, experiments adding 4-AP to the intracellular solution indicate that the inhibitory effects are localized inside the cell. Additionally, 4-AP significantly modifies the properties of steady-state activation and inactivation kinetics of the channel. Our data suggest that the K+ channel blocker 4-AP inhibits both neuron and myoblast Na+ channels via different mechanisms. These findings may also provide information regarding 4-AP-induced pharmacological and toxicological effects in clinical use and experimental research.

Swelling-activated Cl? currents, I(Cl,swell), were measured during hyposmotic shock in white Leghorn embryonic chick heart cells using the whole-cell recording of patch-clamp technique. Genistein, an inhibitor of protein tyrosine kinase (PTK), suppressed I(Cl,swell). Under isosmotic condition phorbol 12-myristate 13-acetate (PMA), an activator of PKC, elicited the Cl? current similar to that in hyposmotic solution, whereas hyposmotic shock did not elicit I(Cl,swell) in chelerythrine chloride(an inhibitor of PKC)-treated cells. Confocal microscopy experiments using FITC-phalloidin as a fluorescent label of F-actin showed that the actin network was moved from cortical region of the cell to the center after hyposmotic shock as compared with the image under isosmotic condition. When the cells were treated with cytochalasin B (CB) or cytochalasin D (CD) under isosmotic condition the disruption of the F-actin integrity was observed, and I(Cl,swell) was not elicited. With combination treatment of CB with PMA, hyposmotic solution could not elicited I(Cl,swell). The results suggested that the role of PTK, probably receptor tyrosine kinase, for regulation of I(Cl,swell) appeared to be at upstream site related to the role of F-actin. Then PKC signal pathway was activated somehow and finally change in the polymerization state of cytoskeleton led to activate the swelling-activated Cl? channels. These results demonstrate clearly that PTK, PKC and F-actin are important factors for regulation of I(Cl,swell), in embryonic chick heart cells as compared with often controversial results reported in different cell types.