Nitroblue tetrazolium blocks BK channels in cerebrovascular smooth muscle cell membranes

• Published in: British journal of pharmacology Vol. 129; no. 5; pp. 1035 - 1041
• Main Authors: Ye, D, Pospisilik, J A, Mathers, D A
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.03.2000; Nature Publishing
• Subjects: Animals; Biological and medical sciences; BK channel; Ca2+‐activated potassium channel; Cell Membrane - drug effects; Cell Membrane - metabolism; Cell membranes. Ionic channels. Membrane pores; Cell structures and functions; Cerebral Arteries - cytology; Cerebral Arteries - drug effects; cerebral artery; channel blocker; Cytoplasm - drug effects; Cytoplasm - metabolism; endothelium; Fundamental and applied biological sciences. Psychology; In Vitro Techniques; Ion Channel Gating - drug effects; Kinetics; Large-Conductance Calcium-Activated Potassium Channels; Membrane Potentials - drug effects; Molecular and cellular biology; Muscle, Smooth, Vascular - drug effects; Muscle, Smooth, Vascular - metabolism; nitric oxide synthase; Nitroblue tetrazolium; Nitroblue Tetrazolium - pharmacology; patch clamp; Patch-Clamp Techniques; Potassium Channel Blockers; Potassium Channels, Calcium-Activated; Rats; Rats, Wistar; smooth muscle; Potassium Cations; Rat; Enzyme; Rodentia; Electrophysiology; Smooth muscle; Patch clamp method; Activation; Ionic channel; Cerebral artery; In vitro; Nitric-oxide synthase; Endothelium; Vertebrata; Mammalia; Blood vessel; Nitroblue tetrazolium test; Oxidoreductases; Antagonist; Circulatory system; Membrane potential; Calcium Cations
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1038/sj.bjp.0703143

The effects of p‐nitroblue tetrazolium (NBT) on large conductance, calcium‐activated potassium channels (BK channels) in enzymatically dispersed rat cerebrovascular smooth muscle cells (CVSMCs) were examined. Patch clamp methods were employed to record single BK channel currents from inside‐out patches of CVMC membrane maintained at 21–23°C. When applied to the cytoplasmic face of inside‐out membrane patches (internally applied NBT), micromolar concentrations of NBT reversible reduced the mean open time of BK channels, without changing channel conductance. NBT altered the frequency distribution of BK channel open times from a two exponential to a single exponential form. In the absence of NBT, mean channel open time increased on membrane depolarization. In the presence of internally applied NBT, mean channel open became essentially independent of membrane potential. Internally applied NBT also reduced the mean closed time of BK channels when measured at membrane potentials in the range −80 mV to +20 mV. The combined effects of internal NBT on mean open and closed times resulted in the suppression of BK channel open probability when measured at positive membrane potentials. When applied to the external membrane face, micromolar concentrations of NBT reduced mean channel open time progressively as the membrane was hyperpolarized, and also reduced open probability at negative membrane potentials. A model is proposed in which NBT alters channel gating by binding to a site at or near to the cytoplasmic membrane face. Externally applied NBT suppressed BK channel open probability at concentrations which also inhibit nitric oxide synthase (NOS). Therefore, the potential role of potassium channel block in NBT actions previously attributed to NOS inhibition is discussed. British Journal of Pharmacology (2000) 129, 1035–1041; doi:10.1038/sj.bjp.0703143