3-Isobutyl-1-methylxanthine (IBMX) affects potassium permeability in rat sensory neurones via pathways that are sensitive and insensitive to [Ca2+]in
✍ Scribed by Yuri Usachev; Platon Kostyuk; Alexej Verkhratsky
- Book ID
- 104746935
- Publisher
- Springer
- Year
- 1995
- Tongue
- English
- Weight
- 984 KB
- Volume
- 430
- Category
- Article
- ISSN
- 0031-6768
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✦ Synopsis
The effects of externally applied 3-isobutyl-1methylxanthine (IBMX), in millimolar concentrations, on the membrane currents in dorsal root ganglia (DRG) neurones isolated from newborn rats were investigated using the amphotericin-based "perforated" patch-clamp technique. In some experiments, simultaneous measurements of intracellular Ca 2+ concentration ([Ca2+]i~) were performed using fura-2 microfluorimetry. Applications of IBMX induced elevation of [Ca2+]in resulting from Ca 2+ release from caffeine-ryanodine-sensitive internal stores. In addition to Ca 2+ release, IBMX produced a biphasic membrane current response comprised of an inward current transiently interrupted by outward current. The onset of the inward current slightly preceded the onset of the [Ca2+]in transient, while the interrupting outward current developed synchronously with the [Ca2+]in rise. The development of IBMX-induced outward current ultimately needed the [Ca2+]in elevation. After the depletion of Ca 2+ stores by IBMX or caffeine exposure, the subsequent IBMX challenge failed to produce both the [Ca2+]in transient and outward membrane current, although the inward current remained unchanged. Both components of the IBMX-induced membrane current response had a reversal potential close to the K + equilibrium potential and the IBMX-induced membrane current response disappeared while dialysing the cell interior with K+-free, Cs+-containing solutions suggesting their association with K + channel activity. External administration of 10 mM tetraethylammonium chloride (TEA-C1) evoked an inward current similar to that observed in response to IBMX; in the presence of TEA-C1, IBMX application was almost