Beta-adrenoceptor activation and PKA regulate delayed rectifier K+ channels of vascular smooth muscle cells.
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 microM 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 approximately 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.
Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina.
E A
EA
Aiello
A T
AT
Malcolm
M P
MP
Walsh
W C
WC
Cole
D015761:4-Aminopyridine / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D051668:Delayed Rectifier Potassium Channels; D004553:Electric Conductivity; D007545:Isoproterenol / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011169:Portal Vein / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D011817:Rabbits; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D013997:Time Factors
D000318:Adrenergic beta-Agonists; D051668:Delayed Rectifier Potassium Channels; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011943:Receptors, Adrenergic, beta; D000255:Adenosine Triphosphate; D015761:4-Aminopyridine; D017868:Cyclic AMP-Dependent Protein Kinases; D007545:Isoproterenol