An unidentified K+ channel in human smooth muscle cells shares properties with both TREK and BKCa channels

MARTÍN PEDRO; ROLDÁN PALOMO ANA ROCÍO; ENRIQUE NICOLÁS; FLORES LUIS EMILIO; REBOLLEDO ALEJANDRO; MILESI VERÓNICA

Salta

Congreso; 3er Reunión de la Sociedad Latinoamericana de Estructura Proteica & XXXIX Congreso de la Sociedad Argentina de Biofísica; 2010

Sociedad Argentina de Biofísica

Our objective was the identification and electrophysiological (patch clamp) characterization of K+ channels in smooth muscle cells enzymatically isolated from human umbilical artery (HUA). We focused on a channel which frequently appeared in the cell-attached (CA) single-channel configuration (symmetrical K+ conditions) in presence of iberiotoxin and 4-aminopyridine. In CA it showed a conductance of 135.3±5.9 pS and an open probability (NPo) of 0.262±0.083 (+40 mV, n=11), which upon patch excision (inside-out, symmetrical K+) changed to a conductance of 251.5±7.8 pS (p<0,05) and NPo = 0.005±0.001 (+40 mV, n=11; p<0.05). In both configurations the NPo presented an exponential voltage dependence. In CA dibutyryl cAMP (200 µM) increased the NPo. In inside-out, lowering the pH (from 7.4 to 6.0) of the bath solution, arachidonic acid (10 µM) produced a significant increase of the channel activity (n=6 in each case). Augmenting the bath Ca2+ concentration (to 1 µM) generated a dramatic increase in NPo and changed its voltage-dependence: now the channel showed a high activity even at hyperpolarized membrane potentials (-40 mV). Bupivacaine (300 µM) provoked a fast block of the channel reducing its conductance (n=4). Cell-attached conductance, activation by acidic pH and arachidonic acid, together with  bupivacaine blockade point to a TREK-like channel. However, classical TREK channels are inhibited by dibutyryl cAMP and increase their NPo upon patch excision, contrary to what our results show. Up to date there are no data regarding its Ca2+ sensitivity. On the other hand, inside-out conductance value, Ca2+ and dibutyryl cAMP activation may point to another identity for this channel, namely a high-conductance Ca2+-activated K channel coupled to a regulatory beta 4 subunit, which confers iberiotoxin insensitivity. Further experiments are required to completely identify this channel.