Abstract
Dihydropyridines and verapamil are widely used as blockers of voltage-dependent Ca ++ channels. In this work we show that these compounds can have a direct blocking action on a class of voltage-activated potassium channels. Voltage-dependent whole-cell currents were recorded from isolated guinea-pig outer hair cells (OHCs) under conditions such that the free Ca ++ concentration in both the internal and external solutions was minimized. A substantial Ca ++-independent K + current was revealed by this procedure. Both conventional K + and Ca ++ channel ligands inhibited this current. The order of potency (in terms of the half inhibitory concentrations (IC 50) of channel inhibitors) was: nimodipine (6 μM) > Bay K 8644 (8 μM) > verapamil (11 μM) >4-aminopyridine (22 μM) > nifedipine (32 μM) > quinine (49 μM) > TEA (10236 μM). Except for verapamil, these channel ligands reduced the size of the K + currents without much alteration of the time course of the currents. In contrast, verapamil caused a more than 10-fold increase in the apparent inactivation rate of the K + currents without significantly altering the activation of the currents. The observation that relatively low concentrations of calcium channel ligands can directly inhibit potassium currents in isolated OHCs indicates that caution should be taken when these pharmacological agents are used as tools for studying cochlear hair cell physiology.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.