Modulation of dihydropyridine receptors in vascular smooth muscle cells by membrane potential and cell proliferation.
We have studied binding of isradipine to A7r5 vascular smooth muscle cells as a function of membrane potential and cell proliferation. Consistent with a voltage-modulated receptor model, two classes of binding sites were detected in confluent cultures: high-affinity sites under depolarizing (50 mM K+) conditions (Kd = 45 +/- 3 pM), and lower affinity sites under resting (5 mM K+) conditions (Kd = 181 +/- 20 pM). However, proliferating cells also displayed the high-affinity state at rest (Kd = 29 +/- 9 pM) in addition to a low-affinity site (Kd = 869 +/- 383 pM). Analysis of dissociation rates also revealed two receptor classes during proliferation. Proliferating cells showed a single class of high-affinity sites (Kd = 39 +/- 6 pM) when depolarized, similar to confluent cells. Receptor density in confluent monolayers increased from 15 +/- 3 fmol/10(6) cells at 5 days to 72 +/- 6 fmol/10(6) cells after 10 days. These results suggest (i) that some L-type Ca2+ channels are spontaneously active in proliferating vascular smooth muscle cells, but require depolarization to activate in a confluent monolayer, and (ii) that the density of dihydropyridine receptors increases after a monolayer becomes confluent.
Ruiz-Velasco
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V
Tulane University School of Medicine, Department of Physiology, New Orleans, LA 70112-2699.
Mayer
M B
MB
Inscho
E W
EW
Hymel
L J
LJ
D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D020746:Calcium Channels, L-Type; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D004095:Dihydropyridines / Q000378:metabolism; D017275:Isradipine / Q000493:pharmacokinetics; D008564:Membrane Potentials / Q000502:physiology; D009124:Muscle Proteins / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D051381:Rats
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D004095:Dihydropyridines; D009124:Muscle Proteins; D017275:Isradipine