Kv1.5 is a major component underlying the A-type potassium current in retinal arteriolar smooth muscle.
Little is known about the molecular characteristics of the voltage-activated K(+) (K(v)) channels that underlie the A-type K(+) current in vascular smooth muscle cells of the systemic circulation. We investigated the molecular identity of the A-type K(+) current in retinal arteriolar myocytes using patch-clamp techniques, RT-PCR, immunohistochemistry, and neutralizing antibody studies. The A-type K(+) current was resistant to the actions of specific inhibitors for K(v)3 and K(v)4 channels but was blocked by the K(v)1 antagonist correolide. No effects were observed with pharmacological agents against K(v)1.1/2/3/6 and 7 channels, but the current was partially blocked by riluzole, a K(v)1.4 and K(v)1.5 inhibitor. The current was not altered by the removal of extracellular K(+) but was abolished by flecainide, indicative of K(v)1.5 rather than K(v)1.4 channels. Transcripts encoding K(v)1.5 and not K(v)1.4 were identified in freshly isolated retinal arterioles. Immunofluorescence labeling confirmed a lack of K(v)1.4 expression and revealed K(v)1.5 to be localized to the plasma membrane of the arteriolar smooth muscle cells. Anti-K(v)1.5 antibody applied intracellularly inhibited the A-type K(+) current, whereas anti-K(v)1.4 antibody had no effect. Co-expression of K(v)1.5 with K(v)beta1 or K(v)beta3 accessory subunits is known to transform K(v)1.5 currents from delayed rectifers into A-type currents. K(v)beta1 mRNA expression was detected in retinal arterioles, but K(v)beta3 was not observed. K(v)beta1 immunofluorescence was detected on the plasma membrane of retinal arteriolar myocytes. The findings of this study suggest that K(v)1.5, most likely co-assembled with K(v)beta1 subunits, comprises a major component underlying the A-type K(+) current in retinal arteriolar smooth muscle cells.
McGahon
Mary K
MK
Centre of Vision Sciences, The Queen's University of Belfast, Institute of Clinical Sciences, The Royal Victoria Hospital, Grosvenor Road, Belfast BT12 6BA. UK.
Dawicki
Jennine M
JM
Arora
Aruna
A
Simpson
D A
DA
Gardiner
T A
TA
Stitt
A W
AW
Scholfield
C Norman
CN
McGeown
J Graham
JG
Curtis
Tim M
TM
D000818:Animals; D001160:Arterioles / Q000378:metabolism; D007150:Immunohistochemistry; D007700:Kinetics; D051666:Kv1.5 Potassium Channel / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D021122:Protein Subunits / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012171:Retinal Vessels / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D051666:Kv1.5 Potassium Channel; D026902:Potassium Channel Blockers; D021122:Protein Subunits; D012333:RNA, Messenger; D011188:Potassium