title: Calcium-sensing receptor: a high-affinity presynaptic target for aminoglycoside-induced weakness.
abstract: Administration of aminoglycoside antibiotics can precipitate sudden, profound bouts of weakness that have been attributed to block of presynaptic voltage-activated calcium channels (VACCs) and failure of neuromuscular transmission. This serious adverse drug reaction is more likely in neuromuscular diseases such as myasthenia gravis. The relatively low affinity of VACC for aminoglycosides prompted us to explore alternative mechanisms. We hypothesized that the presynaptic Ca(2+)-sensing receptor (CaSR) may contribute to aminoglycoside-induced weakness due to its role in modulating synaptic transmission and its sensitivity to aminoglycosides in heterologous expression systems. We have previously shown that presynaptic CaSR controls a non-selective cation channel (NSCC) that regulates nerve terminal excitability and transmitter release. Using direct, electrophysiological recording, we report that neuronal VACCs are inhibited by neomycin (IC(50) 830 +/- 110 microM) at a much lower affinity than CaSR-modulated NSCC currents recorded from acutely isolated presynaptic terminals (synaptosomes; IC(50) 20 +/- 1 microM). Thus, at clinically relevant concentrations, aminoglycoside-induced weakness is likely precipitated by enhanced CaSR activation and subsequent decrease in terminal excitability rather than through direct inhibition of VACCs themselves.
authors: Division of Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, OR 97239, USA.
authors: Mark T
authors: MT
authors: Harnett
authors: Wenyan
authors: W
authors: Chen
authors: Stephen M
authors: SM
authors: Smith
mesh_terms: D000617:Aminoglycosides / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D007473:Ion Channels / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018908:Muscle Weakness / Q000139:chemically induced; D009355:Neomycin / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects* / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D017783:Superior Cervical Ganglion / Q000187:drug effects / Q000502:physiology; D013574:Synaptosomes / Q000187:drug effects / Q000502:physiology
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D007473:Ion Channels; D044169:Receptors, Calcium-Sensing; D009355:Neomycin