Abstract
Effects of membrane potential, intracellular Ca2+ and adenine nucleotides on glucose-sensitive channels from X organ (XO) neurons of the crayfish were studied in excised inside-out patches. Glucose-sensitive channels were selective to K+ ions; the unitary conductance was 112 pS in symmetrical K+, and the K+ permeability (PK) was 1.3 × 10-13 cm · s-1. An inward rectification was observed when intracellular K+ was reduced. Using a quasi-physiological K+ gradient, a non-linear K+ current/voltage relationship was found showing an outward rectification and a slope conductance of 51 pS. The open-state probability (Po) increased with membrane depolarization as a result of an enhancement of the mean open time and a shortening of the longer period of closures. In quasi-physiological K+ concentrations, the channel was activated from a threshold of about -60 mV, and the activation midpoint was — 2 mV. Po decreased noticeably at 50 μM internal adenosine 5′-triphosphate (ATP), and single-channel activity was totally abolished at 1 mM ATP. Hill analysis shows that this inhibition was the result of simultaneous binding of two ATP molecules to the channel, and the half-blocking concentration of ATP was 174 μM. Internal application of 5′-adenylylimidodiphosphate (AMP-PNP) as well as glibenclamide also decreased Po. By contrast, the application of internal ADP (0.1 to 2 mM) activated this channel. An optimal range of internal free Ca2+ ions (0.1 to 10 μM) was required for the activation of this channel. The glucose—sensitive K+ channel of XO neurons could be considered as a subtype of ATP-sensitive K+ channel, contributing substantially to macroscopic outward current.
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Onetti, C.G., Lara, J. & Garcia, E. Adenine nucleotides and intracellular Ca2+ regulate a voltage-dependent and glucose-sensitive potassium channel in neurosecretory cells. Pflügers Arch — Eur J Physiol 432, 144–154 (1996). https://doi.org/10.1007/s004240050116
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DOI: https://doi.org/10.1007/s004240050116