Decrease in acetylcholine-induced current by neomycin in PC12 cells

Antibiotic supplements affect electrophysiological properties and excitability of rat hippocampal pyramidal neurons in primary culture

INTRODUCTION

Antibiotic supplements are regularly used in neuronal culture media to control contamination; however, they can interfere with the neuronal excitability and affect electrophysiological properties. Therefore, in this study, the effect of penicillin/streptomycin supplements on the spontaneous electrophysiological activity of hippocampal pyramidal neurons was examined.

METHODS

Electrophysiological whole-cell patch-clamp recordings from rat hippocampal pyramidal cells in primary culture were performed to investigate the effects of antibiotic supplements on the intrinsic excitability of cultured cells.

RESULTS

The present findings indicated that presence of antibiotic supplements (penicillin/streptomycin) in the culture medium altered the intrinsic electrical activity of hippocampal pyramidal neurons in primary culture. These alterations included: 1) depolarized resting membrane potential; 2) a significant enhancement in the after-hyperpolarization amplitude; 3) a significant increase in the area under the action potential and in the decay and rise time of the action potential; 4) a significant broadening of action potential and 5) a significant reduction in the firing frequency.

CONCLUSION

These findings suggest that addition of antibiotic supplements to culture media influences the neuronal excitability and alters the electrophysiological properties of cultured neurons, possibly through changing the ionic conductance underlying neuronal excitability.

Aminoglycoside antibiotics: structure, functions and effects on in vitro plant culture and genetic transformation protocols

Plant transformation protocols generally involve the use of selectable marker genes for the screening of transgenic material. The bacterial gene nptII, coding for a neomycin phosphotransferase, and the hpt gene, coding for a hygromycin phosphotransferase, are frequently used. These enzymes detoxify aminoglycoside antibiotics by phosphorylation, thereby permitting cell growth in the presence of antibiotics. Nevertheless, the screening for transgenic regenerated shoots is often partial and difficult due to regeneration of escapes and chimeras. These difficulties can be caused, in part, by an incorrect assumption about the mode of action of antibiotics in bacterial and eukaryotic cells and in in vitro tissue culture. The information contained in this review could be useful to establish better selection strategies by taking into account factors such as explant complexity, transformation and selection protocols that allow better accessibility to cells of Agrobacterium and antibiotics, and faster regeneration methods that avoid collateral effects of antibiotics on recovered, putative transgenic shoots.

On the interaction of neomycin with the slow vacuolar channel of Arabidopsis thaliana

This study investigates the interaction of the aminoglycoside antibiotic neomycin with the slow vacuolar (SV) channel in vacuoles from Arabidopsis thaliana mesophyll cells. Patch-clamp experiments in the excised patch configuration revealed a complex pattern of neomycin effects on the channel: applied at concentrations in the submicromolar to millimolar range neomycin (a) blocked macroscopic SV currents in a voltage- and concentration-dependent manner, (b) slowed down activation and deactivation kinetics of the channel, and most interestingly, (c) at concentrations above 10 μM, neomycin shifted the SV activation threshold towards negative membrane potentials, causing a two-phasic activation at high concentrations. Single channel experiments showed that neomycin causes these macroscopic effects by combining a decrease of the single channel conductance with a concomitant increase of the channel's open probability. Our results clearly demonstrate that the SV channel can be activated at physiologically relevant tonoplast potentials in the presence of an organic effector molecule. We therefore propose the existence of a cellular equivalent regulating the activity of the SV channel in vivo.

Unexpected sensitivity of the human α7 neuronal nicotinic acetylcholine receptor to aminoglycosides

The wide use of antibiotics and the development of resistance is a major health concern and, despite their relatively severe side effects, aminoglycoside antibiotics are still used in clinics. Effects of seven aminoglycosides were investigated at the human homomeric alpha7 and heteromeric alpha4beta2 neuronal nicotinic acetylcholine receptors. All aminoglycosides tested inhibited the acetylcholine-evoked responses with more pronounced effects at alpha7 than at alpha4beta2. Neomycin displayed higher blockade with a half inhibition in the nanomolar range at low calcium concentration and in the micromolar range in physiological calcium concentration but still exerted blockade below the concentration used in the clinic. These data suggest that some of their side effects may be attributable to their interactions with neuronal nicotinic acetylcholine receptors.

Voltage-dependent inhibition of rat skeletal muscle sodium channels by aminoglycoside antibiotics

Aminoglycoside (AG) antibiotics interact with numerous biological molecules, including some voltage-gated ion channels. The present study demonstrates that 4,5-disubstituted (neomycin class) and 4,6-disubstituted (kanamycin class) AGs inhibit whole-cell currents through cloned rat skeletal muscle sodium channels (mu1, Na(V)4.1). Increases in the amplitude of the step command reduced inhibition by extracellular AGs but increased inhibition by intracellularly applied AGs, indicating that the block was voltage dependent. Furthermore, intracellular neamine or sisomycin hastened the rate of macroscopic current decay at positive voltages. Extracellular solution containing sodium ions slowed the rate of current decay in the presence of intracellular sisomycin and decreased the apparent affinity of sisomycin from the intracellular side twofold. Current inhibition by extracellularly or intracellularly applied AGs was well fitted by the Woodhull model of pore block. The model indicated that most extracellularly applied AGs interact at a site that is an electrical distance of approximately 10-15% from the outside, whereas intracellularly applied neamine or sisomycin bind to sites that are approximately 49% and approximately 24%, respectively, into the electric field from the inside. Our data suggested that AG antibiotics induce a low-affinity, voltage-dependent block of mu1 channels.