A new benzoxazine compound blocks KATP channels in pancreatic beta cells: molecular basis for tissue selectivity in vitro and hypoglycaemic action in vivo.
OBJECTIVE
The 2-propyl-1,4 benzoxazine (AM10) shows a peculiar behaviour in skeletal muscle, inhibiting or opening the ATP-sensitive K(+) (KATP) channel in the absence and presence of ATP, respectively. We focused on tissue selectivity and mechanism of action of AM10 by testing its effects on pancreatic KATP channels by means of both in vitro and in vivo investigations.


METHODS
In vitro, patch-clamp recordings were performed in native pancreatic beta cells and in tsA201 cells expressing the Kir6.2 Delta C36 channel. In vivo, an intraperitoneal glucose tolerance test was performed in normal mice.


RESULTS
In contrast with what observed in the skeletal muscle, AM10, in whole cell perforated mode, did not augment KATP current (I(KATP)) of native beta cells but it inhibited it in a concentration-dependent manner (IC(50): 11.5 nM; maximal block: 60%). Accordingly, in current clamp recordings, a concentration-dependent membrane depolarization was observed. On excised patches, AM10 reduced the open-time probability of KATP channels without altering their single channel conductance; the same effect was observed in the presence of trypsin in the bath solution. Moreover, AM10 inhibited, in an ATP-independent manner, the K(+) current resulting from expressed Kir6.2 Delta C36 (maximal block: 60% at 100 microM; IC(50): 12.7 nM) corroborating an interaction with Kir. In vivo, AM10 attenuated the glycemia increase following a glucose bolus in a dose-dependent manner, without, at the dose tested, inducing fasting hypoglycaemia.


CONCLUSIONS
Altogether, these results help to gain insight into a new class of tissue specific KATP channel modulators.
Rolland
J-F
JF
Department of Pharmacobiology, Unit of Pharmacology, Faculty of Pharmacy, University of Bari, Bari, Italy.
Tricarico
D
D
Laghezza
A
A
Loiodice
F
F
Tortorella
V
V
Camerino
D Conte
DC
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D048588:Benzoxazines / Q000494:pharmacology*; D001786:Blood Glucose / Q000187:drug effects*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005951:Glucose Tolerance Test; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D066298:In Vitro Techniques; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009154:Mutation; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D012016:Reference Values; D013997:Time Factors; D014162:Transfection; D000099161:Kcnj11 Channel
D000255:Adenosine Triphosphate; D000631:Aminopyridines; D048588:Benzoxazines; D001786:Blood Glucose; D007004:Hypoglycemic Agents; D026902:Potassium Channel Blockers; D024661:Potassium Channels, Inwardly Rectifying; D000099161:Kcnj11 Channel; C516673:6-chloro-2-propyl-3-(pyrid-3-ylamino)-2H-1,4-benzoxazine