Abstract
The effects of externally applied 3-isobutyl-1-methylxanthine (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 Ca2+ concentration ([Ca2+]in) were performed using fura-2 microfluorimetry. Applications of IBMX induced elevation of [Ca2+]in resulting from Ca2+ release from caffeine-ryanodine-sensitive internal stores. In addition to Ca2+ 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 Ca2+ 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-Cl) evoked an inward current similar to that observed in response to IBMX; in the presence of TEA-Cl, IBMX application was almost unable to induce additional inward current. IBMX (5 mM) effectively (≈50%) inhibited K+ currents evoked by step depolarizations of membrane potential. We suggest that IBMX affects membrane permeability via activation of Ca2+-regulated K+ channels and direct inhibition of TEA-sensitive K+ channels.
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Usachev, Y., Kostyuk, P. & Verkhratsky, A. 3-Isobutyl-1-methylxanthine (IBMX) affects potassium permeability in rat sensory neurones via pathways that are sensitive and insensitive to [Ca2+]in . Pflügers Arch 430, 420–428 (1995). https://doi.org/10.1007/BF00373918
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DOI: https://doi.org/10.1007/BF00373918