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Am J Physiol Heart Circ Physiol 275: H448-H459, 1998;
0363-6135/98 $5.00
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Vol. 275, Issue 2, H448-H459, August 1998

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

E. Alejandro Aiello1, A. Todd Malcolm2, Michael P. Walsh2, and William C. Cole2

1 Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina; and 2 The Smooth Muscle Research Group, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada T2N 4N1

Macroscopic 4-aminopyridine (4-AP)-sensitive, delayed rectifier K+ current of vascular smooth muscle cells is increased during beta -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 (NPo) 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 NPo 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 KDR channel activity and caused NPo 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 KDR channels 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 beta -adrenoceptors and phosphorylation by PKA at a membrane potential consistent with that observed in the myocytes in situ.

isoproterenol; adenosine 3',5'-cyclic monophosphate-dependent protein kinase; 4-aminopyridine; protein kinase A


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