A late slow depolarization unmasked in the presence of tetraethylammonium in neonatal rat sympathetic neurons in vitro

The inhibitory effects of nano-Ag on voltage-gated potassium currents of hippocampal CA1 neurons

The application of the nano-sized materials continues to grow at a rapid rate in the fields of medicine, biotechnology, and environmental technology. Voltage-gated potassium currents play a key role in excitable cellular viability and function, especially in the central nervous system. The aim of this study was to investigate the actions of silver nano-particles (nano-Ag) on voltage-activated potassium currents in hippocampal CA1 neurons using whole cell patch-clamp technique. The hydrodynamic mean diameter of nano-Ag (10(-5) g mL(-1) ) was 223.9 nm in artificial cerebrospinal fluid (ACSF). Both types, transient potassium (I(A) ) and delayed rectifier potassium (I(K) ) current amplitudes were inhibited by the nano-Ag (10(-5) g mL(-1) ). The nano-Ag particles produced a hyperpolarizing shift in the activation-voltage curve of I(K) and inactivation-voltage curve of I(A) and also delayed the recovery of I(A) from inactivation. The results suggest that nano-Ag may have potential to alter the excitability of neurons by depressing the potassium channels.

Effects of pineal factors on the action potentials of sympathetic neurons

Neurons from rat superior cervical ganglia were grown in coculture with pineal cells. Action potentials of neurons in cocultures were 25% longer and were 25% greater in amplitude than those recorded from neurons grown in the presence of ganglionic nonneuronal cells alone. Neurons showed an increase in action potential duration with increasing time in culture. This may have been related to the recovery of nonneuronal cell populations after an initial exposure to the antimitotic agent Ara-C. In cultures not initially exposed to Ara-C, a subsequent exposure after 7 days in culture resulted in a shortening of the action-potential duration. Neuronal cultures were exposed to gel slabs containing the pineal indolamines, serotonin, N-acetylserotonin, and melatonin. Serotonin and N-acetylserotonin showed no effect on the neuronal action potentials at the concentrations tested. Melatonin caused an increase in action-potential duration that was associated not with an increase in action-potential amplitude, but with a decrease in action-potential rise rates. The effects of long-term exposure in melatonin appeared to be reversible in some cells but not in all. Short-term effects of melatonin were observed in older cultures and in younger cultures after the cells were stimulated repeatedly. Older cultures also had higher levels of spontaneous activity. The dependence of the short-term effects of melatonin on electrical activity may suggest a role for melatonin as a neuromodulator.

Calcium-dependent action potentials in guinea-pig olfactory cortex neurones

Ca2+-dependent action potentials were recorded in guinea pig olfactory neurones in vitro (23 degrees--25 degrees C). In most cells (in the presence of tetrodotoxin: TTX) the current-voltage relationship displayed 'anomalous' rectification (apparent high slope resistance) at potentials approximately 20 mV depolarized to the resting membrane potential (approximately -80 mV) and strong outward rectification at more positive potentials. Intracellular Cs+-loading blocked outward rectification and increased action potential duration. Such spikes were TTX-insensitive and were further prolonged by external addition of tetraethylammonium (TEA) or Ba2+. Spikes recorded from Cs+-loaded, TTX/TEA-treated neurones displayed a prolonged plateau and an after-depolarization. They persisted when Ba2+ or Sr2+ were substituted for external Ca2+, but not when Mg2+ was the sole extracellular divalent cation. The spikes were blocked in the presence of Cd2+ but persisted when 82% of the extracellular Na+ was substituted by choline. A TTX-insensitive, slowly inactivating inward current at depolarized potentials is believed to account for the subthreshold 'anomalous' rectification and prolonged spike plateau.