Glucose reduces endothelin inhibition of voltage-gated potassium channels in rat arterial smooth muscle cells.
Prolonged hyperglycaemia impairs vascular reactivity and inhibits voltage-activated K(+) (Kv) channels. We examined acute effects of altering glucose concentration on the activity and inhibition by endothelin-1 (ET-1) of Kv currents of freshly isolated rat arterial myocytes. Peak Kv currents recorded in glucose-free solution were reversibly reduced within 200 s by increasing extracellular glucose to 4 mm. This inhibitory effect of glucose was abolished by protein kinase C inhibitor peptide (PKC-IP), and Kv currents were further reduced in 10 mm glucose. In current-clamped cells, membrane potentials were more negative in 4 than in 10 mm glucose. In 4 mm d-glucose, 10 nm ET-1 decreased peak Kv current amplitude at +60 mV from 23.5 +/- 3.3 to 12.1 +/- 3.1 pA pF(-1) (n = 6, P < 0.001) and increased the rate of inactivation, decreasing the time constant around fourfold. Inhibition by ET-1 was prevented by PKC-IP. When d-glucose was increased to 10 mm, ET-1 no longer inhibited Kv current (n = 6). Glucose metabolism was required for prevention of ET-1 inhibition of Kv currents, since fructose mimicked the effects of d-glucose, while l-glucose, sucrose or mannitol were without effect. Endothelin receptors were still functional in 10 mm d-glucose, since pinacidil-activated ATP-dependent K(+) (K(ATP)) currents were reduced by 10 nm ET-1. This inhibition was nearly abolished by PKC-IP, indicating that endothelin receptors could still activate PKC in 10 mm d-glucose. These results indicate that changes in extracellular glucose concentration within the physiological range can reduce Kv current amplitude and can have major effects on Kv channel modulation by vasoconstrictors.
Rainbow
R D
RD
Department of Cell Physiology and Pharmacology, University of Leicester, PO Box 138, Leicester LE1 9HN, UK.
Hardy
M E L
ME
Standen
N B
NB
Davies
N W
NW
D000818:Animals; D019332:Endothelin-1 / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D006943:Hyperglycemia / Q000378:metabolism; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D008297:Male; D008564:Membrane Potentials; D008638:Mesenteric Arteries / Q000187:drug effects / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D024642:Potassium Channels, Voltage-Gated / Q000187:drug effects* / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
D019332:Endothelin-1; D026902:Potassium Channel Blockers; D024642:Potassium Channels, Voltage-Gated; D047428:Protein Kinase Inhibitors; D014662:Vasoconstrictor Agents; D011493:Protein Kinase C; D005947:Glucose