β-Adrenoceptor activation and PKA regulate delayed rectifier K⁺channels of vascular smooth muscle cells

Abstract

Macroscopic 4-aminopyridine (4-AP)-sensitive, delayed rectifier K+ current of vascular smooth muscle cells is increased during β-adrenoceptor activation with isoproterenol via a signal transduction pathway involving adenylyl cyclase and cAMP-dependent protein kinase (PKA) (Aiello, E. A., M. P. Walsh, and W. C. Cole. Am. J. Physiol. 268 ( Heart Circ. Physiol. 37): H926–H934, 1995.). In this study, we identified the single delayed rectifier K+(KDR) channel(s) of rabbit portal vein myocytes affected by treatment with isoproterenol or the catalytic subunit of PKA. 4-AP-sensitive KDR channels of 15.3 ± 0.6 pS ( n = 5) and 14.8 ± 0.6 pS ( n = 5) conductance, respectively, were observed in inside-out (I-O) and cell-attached (C-A) membrane patches in symmetrical KCl recording conditions. The kinetics of activation (time constant of 10.7 ± 3.02 ms) and inactivation (fast and slow time constants of 0.3 and 2.5 s, respectively) of ensemble currents produced by these channels mimicked those reported for inactivating, 4-AP-sensitive whole cell KDR current of vascular myocytes. Under control conditions, the open probability ( NP o) of KDR channels of C-A membrane patches at −40 mV was 0.014 ± 0.005 ( n = 8). Treatment with 1 μM isoproterenol caused a significant, approximately threefold increase in NP o to 0.041 ± 0.02 ( P < 0.05). KDR channels of I-O patches exhibited rundown after ∼5 min, which was not affected by ATP (5 mM) in the bath solution. Treatment with the purified catalytic subunit of PKA (50 nM; 5 mM ATP) restored KDRchannel activity and caused NP o to increase from 0.011 ± 0.003 to 0.138 ± 0.03 ( P < 0.05; n = 11). These data indicate that small-conductance, 15-pS KDRchannels are responsible for inactivating the macroscopic delayed rectifier K+ current of rabbit portal vein myocytes and that the activity of these channels is enhanced by a signal transduction mechanism involving β-adrenoceptors and phosphorylation by PKA at a membrane potential consistent with that observed in the myocytes in situ.

Molecular Composition of 4-Aminopyridine-Sensitive Voltage-Gated K + Channels of Vascular Smooth Muscle

“…4,5,8,9,11,24 This level of 4-AP sensitivity and the biophysical properties of the currents are consistent with those previously identified for Kv1-containing, 11,17,[22][23][24][25][26] but not Kv2-to 4-containing, 26 -31 Kv channels. The properties of whole-cell and unitary currents due to expression of Kv1.5 cloned from RPV closely mimicked those of native RPV K DR channels.…”

“…[1][2][3][4][5][6]11,24 We attribute the K TO component to the expression of Kv1.4, but it is unlikely that this subunit contributes substantially to the K DR current. Whole-cell currents, as a result of the expression of Kv1.4 in heterologous cell types, 25,40 exhibit several characteristics consistent with those of vascular K TO currents.…”

“…6 4-AP-sensitive K DR channels are thought to contribute to the control of membrane potential in vascular myocytes. [1][2][3]7 This view is supported by (1) electrophysiological evidence that K DR channels are active at voltages consistent with the membrane potential of vascular myocytes [1][2][3][4][5] and (2) pharmacological evidence indicating that submillimolar 4-AP inhibits K DR currents of vascular myocytes [1][2][3][4][5] and elicits depolarization and contraction of intact blood vessels. 1,2,7 Moreover, the activity of vascular 4-AP-sensitive K DR channels is modulated by agonists that signal through protein kinases A and C 4,5,8,9 and may contribute to the physiological regulation of arterial diameter by locally released or circulating vasoactive factors.…”

“…1,2 Alterations in K ϩ channel activity modulate the level of membrane potential and, thereby, cytosolic free Ca 2ϩ concentration and contractile filament activation. 1,2 Voltage-dependent outward current of vascular myocytes is due to at least three components: a slowly inactivating 4-aminopyridine (4-AP)-sensitive delayed rectifier (K DR ) current [1][2][3][4][5][6] ; a 4-AP-insensitive outward current 5 ; and a rapidly inactivating, 4-AP-sensitive transient A-type current (K TO ). 6 4-AP-sensitive K DR channels are thought to contribute to the control of membrane potential in vascular myocytes.…”

Gender-specific K+-channel contribution to adenosine-induced relaxation in coronary arterioles

“…These investigators also reported that adenosine-mediated K ϩ -channel activation is coupled with endothelium-derived nitric oxide production (13). The role of voltage-dependent K ϩ (K V ) channels in adenosine-mediated relaxation has not been reported previously; however, findings of Aiello et al (1,2) provide evidence that both protein kinase A (PKA) and isoproterenol stimulate K V channels in isolated vascular smooth muscle cells. Although controversial, adenosine has been reported to act via cAMP and PKA in vascular smooth muscle (16), providing a putative mechanism for K V -channel activation by adenosine.…”