ZD 7288

ZD 7288 is an inhibitor of hyperpolarization-activated cyclic nucleotide-gated (HCN) channel [1].

The HCN channel is found in the sinoatrial node (SAN) and is permeable to both Na+ and K+. The HCN current exists in neurons under hyperpolarization of the cell membrane and plays an important role in neuropathic pain [1].

In CA1 pyramidal cells from Wistar rats, ZD 7288 inhibited T-type Ca2+ channel currents in a concentration-dependant way [2]. In neonatal rat facial motoneurones, ZD-7288 (0.1-10 μM) inhibited the hyperpolarisation-activated current with IC50 value of 0.2 μM in a time- and voltage-dependent way [3]. In CA1 pyramidal neurons, ZD 7288 (1-1000 μM) inhibited the hyperpolarization-activated current. However, ZD 7288 had no influence on long-term depression (LTD) of the CA3-CA1 synapse [4].

In rats with chronic visceral pain, ZD 7288 (50-100 nM) significantly inhibited abdominal withdrawal reflex (AWR) scores and electromyographic (EMG) responses. Also, ZD 7288 significantly increased pain thresholds. These results suggested that spinal HCN channels might play a critical role in chronic visceral pain [1].

References:
[1].  Chen Y, Lin C, Tang Y, et al. ZD 7288, an HCN channel blocker, attenuates chronic visceral pain in irritable bowel syndrome-like rats. World J Gastroenterol, 2014, 20(8): 2091-2097.
[2].  Sánchez-Alonso JL, Halliwell JV, Colino A. ZD 7288 inhibits T-type calcium current in rat hippocampal pyramidal cells. Neurosci Lett, 2008, 439(3): 275-280.
[3].  Larkman PM, Kelly JS. Modulation of the hyperpolarisation-activated current, Ih, in rat facial motoneurones in vitro by ZD-7288. Neuropharmacology, 2001, 40(8): 1058-1072.
[4].  Gasparini S, DiFrancesco D. Action of the hyperpolarization-activated current (Ih) blocker ZD 7288 in hippocampal CA1 neurons. Pflugers Arch, 1997, 435(1): 99-106.

Modulation of the hyperpolarisation-activated current, Ih, in rat facial motoneurones in vitro by ZD-7288.[Pubmed:11406198]

Neuropharmacology. 2001 Jun;40(8):1058-72.

ZD-7288 [4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyrimidinium chloride] and Cs(+) have been used to distinguish the currents contributing to inward rectification in neonatal rat facial motoneurones (FMs). ZD-7288 (0.1-10 microM) inhibited a current that reversed at -43.7+/-3.7 mV in artificial cerebrospinal fluid (ACSF) containing 3 mM K(+) (n=9), and displayed the time and voltage dependence of the hyperpolarisation-activated current, I(h). Depolarisation-activated transient (I(K(A))) and sustained outward currents were unaffected by ZD-7288. The IC(50) for block of I(h) by ZD-7288 was around 0.2 microM. Onset of inhibition was slow and no recovery was seen after washing in ZD-7288-free ACSF for up to 4 h. In the presence of ZD-7288, Ba(2+) and Rb(+) blocked an inwardly rectifying potassium (K(+)) current, confirming both the presence of I(K(IR)) and its insensitivity to ZD-7288. Cs(+) rapidly and reversibly blocked both I(h) and I(K(IR)). Inhibition of I(h) by ZD-7288 showed no use dependence, internally applied ZD-7288 also blocked I(h), and tail current analysis indicated inhibition to be voltage-independent. In the presence of internal guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S) and after previous exposure to ZD-7288, 5-hydroxytryptamine (5-HT), but not noradrenaline, promoted a recovery of I(h) that was not observed if ZD-7288 was present throughout the recording period. This interaction between ZD-7288 and irreversible 5-HT-receptor activation may be related to the mechanism underlying ZD-7288-mediated block of these channels.

ZD 7288, an HCN channel blocker, attenuates chronic visceral pain in irritable bowel syndrome-like rats.[Pubmed:24587682]

World J Gastroenterol. 2014 Feb 28;20(8):2091-7.

AIM: To investigate the effects of ZD 7288, a hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blocker, on rats with chronic visceral pain. METHODS: Rats with visceral hypersensitivity were generated using neonatal colon irritation during postnatal days 8-15 as described previously. Visceral hypersensitivity was evaluated using electromyographic (EMG) responses of abdominal external oblique muscles to 20-80 mmHg colorectal distentions (CRD). Abdominal withdrawal reflex (AWR) scores and pain thresholds were also detected in adult rats. Different doses of ZD 7288 (25, 50, and 100 nmol/L) were intrathecally administered in rats to study the role of spinal HCN channel in chronic visceral hypersensitivity. RESULTS: EMG responses to 20-80 mmHg CRD and AWR scores under 20-60 mmHg CRD significantly increased in rats with visceral hypersensitivity compared to control rats (P < 0.05). The pain threshold in rats with visceral hypersensitivity significantly decreased compared to control rats (P < 0.05). Treatment with 50-100 nmol/L ZD 7288 significantly inhibited EMG responses (16%-62%, 80-20 mmHg CRD, P < 0.05) and AWR scores (24%-37%, 40-20 mmHg CRD, P < 0.05; 12%-61%, 80-20 mmHg CRD, P < 0.05, respectively), and significantly increased pain thresholds (32%-77%, P < 0.05). CONCLUSION: Spinal HCN channels may play an important role in chronic visceral hypersensitivity.

Action of the hyperpolarization-activated current (Ih) blocker ZD 7288 in hippocampal CA1 neurons.[Pubmed:9359908]

Pflugers Arch. 1997 Dec;435(1):99-106.

The effects of ZD 7288, a "bradycardic" agent, in young rat hippocampal slices in vitro were studied. ZD 7288 (1-1000 microM) reduced the hyperpolarization-activated current (Ih) in CA1 pyramidal neurons by a voltage-independent blocking mechanism. Under current-clamp conditions, the bradycardic agent (10 microM) caused membrane hyperpolarization (by 5.9 +/- 0.5 mV) and a reduction of membrane conductance (by 17.9 +/- 4.1%). These data are consistent with the block of an inward current which is active at rest. The drug-induced hyperpolarization depressed the cell's excitability by increasing the threshold current necessary to induce firing. When the drug-induced hyperpolarization was compensated for by injection of a tonic depolarizing current, ZD 7288 caused a reduction of the inhibitory post-synaptic potential (IPSP) in EPSP-IPSP sequences. Since Cs+, another known blocker of Ih, is able to reverse long-term depression (LTD) of the CA3-CA1 synapse in hippocampal slices, we tested the effect of ZD 7288 on synaptic transmission. We found that ZD 7288 did not significantly modify LTD, suggesting that Cs+-induced inhibition of LTD maintenance is not directly related to block of Ih.

ZD 7288 inhibits T-type calcium current in rat hippocampal pyramidal cells.[Pubmed:18534748]

Neurosci Lett. 2008 Jul 18;439(3):275-80.

Many studies have used the channel blocker ZD 7288 to assess possible physiological and pathophysiological roles of hyperpolarization-activated cation currents (Ih). In view of the known interplay between Ih and other membrane conductances, the effects in Wistar rats of ZD 7288 on low-voltage-activated (LVA (- or T-type)) Ca2+ channels were examined in whole-cell patch-clamp recordings from CA1 pyramidal cells in the presence of TTX, TEA, 4-AP, CsCl, BaCl2 and nifedipine. ZD 7288 reduced T-type calcium channel currents and this effect was concentration dependant. ZD 7288 blocked T-type currents when applied extracellularly, but not when included in the recording pipette. Furthermore, ZD 7288 altered the steady-state voltage-dependent inactivation of T-currents. These results indicate that the blocker ZD 7288 has effects on voltage sensitive channels additional to those reported for the Ih current.

Ih channels as modulators of presynaptic terminal function: ZD7288 increases NMDA-evoked [3H]-noradrenaline release in rat neocortex slices.[Pubmed:12690435]

Naunyn Schmiedebergs Arch Pharmacol. 2003 Apr;367(4):422-5.

Recent observations indicate the presence of hyperpolarization-activated cation channels (I(h) channels) in presynaptic terminals of central neurons, but their functional impact is still unclear. To investigate whether there are operative I(h) channels on presynaptic terminals of noradrenergic neurons, the effect of the I(h) channel blocker ZD7288 on the N-methyl-D-aspartate (NMDA)-evoked [3H]-noradrenaline release ([3H]-NA release) was tested. Neocortical slices of the rat, preloaded with [(3)H]-NA, were superfused in the presence of TTX (0.32 microM) and stimulated twice by addition of 300 microM NMDA. Application of 1 and 10 microM ZD7288 increased the NMDA-evoked [(3)H]-NA release by 29 and 44%, respectively, in the presence of 3 mM external K+. Elevation of external K+ to 6 mM significantly reduced the increasing effect of 10 microM ZD7288 to 15% only. Our results indicate the presence of I(h) channels on presynaptic terminals of noradrenergic neurons and suggest that presynaptic I(h) channels may attenuate transmitter release, at least under the present test conditions.

Pharmacological characterization of the inwardly-rectifying current in the smooth muscle cells of the rat bladder.[Pubmed:8982495]

Br J Pharmacol. 1996 Dec;119(8):1509-18.

1. In freshly-isolated single cells of the rat bladder detrusor, outwardly-rectifying and inwardly-rectifying membrane currents were identified by the whole-cell voltage-clamp technique. 2. The inwardly-rectifying current (IIR) exhibited features of a cation current permeable to both K+ and Na+ but it was unaffected by changes in extracellular Ca2+. It had an activation threshold close to -60 mV and an estimated reversal potential of -29 mV. 3. IIR activated slowly with a voltage-sensitive time-constant of 69 ms at -140 mV and 209 ms at -100 mV but did not exhibit time-dependent inactivation. 4. IIR was unaffected by tetraethylammonium (up to 20 mM) but it was reduced by extracellular Ba2+ (1 mM) and by extracellular Cs+ (1 mM). 5. IIR was reduced by terikalant (100 microM) and markedly inhibited by ciclazindol (100 microM) although at these concentrations, both agents also reduced outward currents. 6. IIR was inhibited by ZD7288 (10-100 microM) in a concentration-dependent manner. At concentrations up to 30 microM, ZD7288 did not reduce the magnitude of outward currents but these were inhibited by 100 microM ZD7288. 7. In strips of bladder detrusor, spontaneous mechanical activity was increased by ZD7288 (0.3-100 microM) and by ciclazindol (0.3-100 microM) but was unaffected by glibenclamide (1-10 microM). 8. It is concluded that IIR closely resembles the hyperpolarization-activated current Ih, previously described in the smooth muscle of rabbit jejunum and in a variety of other cell types. This current may play an important role in modulating detrusor excitability but this could not be confirmed using the inhibitors ZD7288 and ciclazindol.

Mechanism of block by ZD 7288 of the hyperpolarization-activated inward rectifying current in guinea pig substantia nigra neurons in vitro.[Pubmed:8747199]

J Neurophysiol. 1995 Dec;74(6):2366-78.

1. The effects of the novel bradycardic agent 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyrimidinium chloride (ZD 7288) (Zeneca) were investigated on the hyperpolarization-activated cationic current (Ih) in guinea pig substantia nigra pars compacta neurons in vitro, using a single-microelectrode current-clamp/voltage-clamp technique. 2. Under current-clamp conditions, injection of large negative current pulses (0.1-0.5 nA, 400 ms) evoked a slow depolarizing "sag" in the electrotonic potential due to activation of the slow inward (anomalous) rectifier. In voltage-clamp recordings, hyperpolarizing voltage steps from a holding potential of -60 mV (close to resting potential) elicited slow inward current relaxations with kinetic properties similar to those seen for other neuronal Ihs. 3. ZD 7288 (10-100 microM) produced a consistent abolition of the electrotonic potential sag with no effect on membrane potential or spike properties. Under voltage clamp, Ih amplitude was clearly reduced in a time- and concentration-dependent manner (apparent half-maximum blocking concentration = 2 microM); full block of Ih was typically achieved after 10-15 min of exposure to 50 microM ZD 7288, with no significant recovery observed after 1 h of washing. 4. A similar (although more rapid) block of Ih was seen after application of 3-5 mM Cs+ (partially reversible after 30 min of washing). 5. Partial block of Ih by 10 microM ZD 7288 was accompanied by a reduction in the maximum amplitude of the Ih activation curve, a small negative shift in its position on the voltage axis, and a linearization of the steady-state current-voltage relationship. The estimated Ih reversal potential, however, remained unaffected. 6. In 10 microM ZD 7288, the time course of Ih activation and deactivation was significantly slowed (within the range of -70 to -120 mV for the activation time constant and -70 to -90 mV for the inactivation time constant). 7. Blockade of Ih by ZD 7288 or Cs+ was independent of prior Ih activation (i.e., non-use dependent). 8. Intracellular loading with ZD 7288 also abolished the sag in the electrotonic voltage response and Ih relaxations, suggesting an intracellular site of action. By contrast, intracellular Cs+ had no effect on Ih properties. 9. Block of Ih by ZD 7288 (but not Cs+) was relieved by prolonged cell hyperpolarization, manifested as a slowly developing (half-time approximately 20 s) inward current at a holding potential of -100 mV. 10. We propose that ZD 7288, when applied externally, may behave as a "lipophilic" quaternary cation, capable of passing into the cell interior to block Ih channels in their closed state; this compound may thus prove a useful research tool, in place of Cs+, for studying the properties and significance of Ih currents in controlling neuronal function.