Adenine nucleotides and intracellular Ca2+ regulate a voltage-dependent and glucose-sensitive potassium channel in neurosecretory cells.
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 x 10(-13) cm x 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-physio- logical 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 microM 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 microM. 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 microM) 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.
Onetti
C G
CG
Centro de Investigaciones Biomédicas, Universidad de Colima, Apdo. Postal 199, C.P. 28000, Colima, Col. Mexico.
Lara
J
J
García
E
E
D000227:Adenine Nucleotides / Q000502:physiology*; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D003400:Astacoidea; D002118:Calcium / Q000378:metabolism*; D004553:Electric Conductivity; D004594:Electrophysiology; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008297:Male; D009490:Neurosecretory Systems / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology*
D000227:Adenine Nucleotides; D015221:Potassium Channels; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D005947:Glucose; D011188:Potassium; D002118:Calcium