Inhibition of N/OFQ on transient outward potassium currents in acutely dissociated rat cerebral parietal cortical neurons / 中国应用生理学杂志

<p><b>AIM</b>To study the effect of Nociceptin/orphanin FQ (N/OFQ) on transient outward potassium (I(A)) in rat cerebral cortical neurons and its kinetic mechanism.</p><p><b>METHODS</b>The effects of N/OFQ on I(A) were investigated by using the whole cell patch clamp technique in acutely dissociated rat cerebral cortical neurons.</p><p><b>RESULTS</b>(1) At the voltage of + 60 mV, 0.1 micromol/L N/OFQ made I(A) decreased from (5356.1 +/- 361.6) pA to (4113.3 +/- 312.7) pA (P < 0.01, n = 10) and the percent inhibition was 23.2% +/- 2.2%. (2) (N/OFQ made I-V curve of I(A) decreased significantly (P < 0.01, n = 10).(3) 0.1 micromol/L N/OFQ shifted the activation curve of I(A) to positive potential from (-9.2 +/- 2.5)mV to (30.6 +/- 3.7) mV (P < 0.01, n = 8) and changed the slope factor(kappa) of the activation curve from (20.4 +/- 2.3) mV to (22.6 +/- 2.1) mV (P > 0.05, n = 8). (4) 0.1 micromol/L N/OFQ caused a significant hyperpolarizing shift of the inactivation curve from (-64.1 +/- 3.2) mV to (-55.9 +/- 1.9) mV (P < 0.05, n = 5), without significant effect on kappa of the inactivation curve.</p><p><b>CONCLUSION</b>0.1 micromol/L N/OFQ has a significant inhibition on I(A) and shift the activation and inactivation curve to depolarization in cerebral parietal cortical neurons of rats.</p>

Inhibition of ACh on the delayed rectifier-like potassium current in acutely isolated cerebral cortical neurons of rats / 生理学报

The modulation of ACh on delayed rectifier-like potassium currents (I(K)) was studied in freshly dissociated cerebral cortical neurons using the whole-cell patch-clamp technique. Wistar rats between 10- and 14-day old of both sexes were used. After rats were decapitated, their brains were quickly removed, iced, and then manually cut into 400 mum slices. Slices were then incubated for 0.5 h at 32 degrees C in a buffered artificial cerebrospinal fluid (ACSF) bubbled with 95% O2, 5% CO2. Slices were then removed into buffered ACSF containing protease (0.5 mg/ml) at 32 degrees C. After 30 min of enzyme digestion, tissue was rinsed three times in the buffered saline. Then the enzyme-treated slices were mechanically dissociated with a graded series of fire-polished Pasteur pipettes. The cell suspension was then plated into a 35 mm dish and placed on the stage of a Olympus inverted microscope. For whole-cell recordings of currents, standard voltage-clamp techniques were used. Neurons were held at -80 mV, and the I(K) was evoked by 2 000 ms depolarizing voltage commands to potential between -40 mV and +60 mV in 10 mV steps applied at a frequency of 0.5 Hz. It was found that the inhibitory effect of ACh (0.1, 1, 10, 100 mumol/L) on I(K) was dose-dependent. It was also found that ACh affected the activation process of I(K) significantly, i.e., the activation curve of I(K) was characterized by half-activation potential of (-41.8+/-9.7) mV and a slope factor of (30.7+/-7.2) mV in the cortical neurons and they were changed to (-122.4+/-38.6) mV and (42.4+/-7.0) mV, respectively, after giving ACh (10 mumol/L). Tubocurarine (100 mumol/L) antagonized the inhibitory effect of ACh on I(K), and the drop of currents varied from the control value of (36.5+/-7..8)% to (16.9+/-13.8)% (n=8, P<0.01). 4-DAMP (10 mumol/L) blocked the inhibitory effect of ACh on I(K), and the currents reduced from the control value of (36.5+/-7.8)% to (26.8+/-4.7) % (n=6, P<0.05). Pirenzepin did not antagonize the inhibition of ACh on I(K) (n=7, P>0.05). Chelerythrine (20 mumol/L) blocked the inhibitory effect of ACh on I(K) and the currents reduced from the control value of (36.5+/-7.8)% to (11.7+/-17.3)% (n=6, P<0.05). On the contrary, PDBu (10 mumol/L) strengthened the inhibition of ACh on I(K) and the drop of currents changed from the control value of (36.5+/-7.8)% to (59.2+/-14.0)% (n=5, P<0.05). PDBu abolished the antagonism of chelerythrine on ACh in cortical neurons. It is suggested that the ACh-induced depolarization of neurons in the cortex is attributed to the inhibition of I(K) that is most likely evoked by the activation of nicotinic ACh receptors and muscarinic M3 receptor via protein kinase C (PKC) signal transduction pathway.