Blockade of insulin sensitive steady-state R-type Ca2+ channel by PN 200-110 in heart and vascular smooth muscle.
The effect of high K+ concentration, insulin and the L-type Ca2+ channel blocker PN 200-110 on cytosolic intracellular free calcium ([Ca2+]i) was studied in single ventricular myocytes of 10-day-old embryonic chick heart, 20-week-old human fetus and rabbit aorta (VSM) single cells using the Ca(2+)-sensitive fluorescent dye, Fura-2 microfluorometry and digital imaging technique. Depolarization of the cell membrane of both heart and VSM cells with continuous superfusion of 30 mM [K+]o induced a rapid transient increase of [Ca2+]i that was followed by a sustained component. The early transient increase of [Ca2+]i by high [K+]o was blocked by the L-type calcium channel antagonist nifedipine. However, the sustained component was found to be insensitive to this drug. PN 200-110 another L-type Ca2+ blocker was found to decrease both the early transient and the sustained increase of [Ca2+]i induced by depolarization of the cell membrane with high [K+]o. Insulin at a concentration of 40 to 80 microU/ml only produced a sustained increase of [Ca2+]i that was blocked by PN 200-110 or by lowering the extracellular Ca2+ concentration with EGTA. The sustained increase of [Ca2+]i induced by high [K+]o or insulin was insensitive to metabolic inhibitors such as KCN and ouabain as well to the fast Na+ channel blocker, tetrodotoxin and to the increase of intracellular concentrations of cyclic nucleotides. Using the patch clamp technique, insulin did not affect the L-type Ca2+ current and the delayed outward K+ current. These results suggest that the early increase of [Ca2+]i during depolarization of the cell membrane of heart and VSM cells with high [K+]o is due to the opening and decay of an L-type Ca2+ channel. However, the sustained increase of [Ca2+]i during a sustained depolarization is due to the activation of a resting (R) Ca2+ channel that is insensitive to lowering [ATP]i and sensitive to insulin.
Bkaily
G
G
Dept of Physiology and Biophysics, Faculty of Medicine, University of Sherbrooke, Quebec, Canada.
Economos
D
D
Potvin
L
L
Ardilouze
J L
JL
Marriott
C
C
Corcos
J
J
Bonneau
D
D
Fong
C N
CN
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D002642:Chick Embryo; D003592:Cytophotometry; D016257:Fura-2; D006321:Heart / Q000187:drug effects* / Q000196:embryology; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D017275:Isradipine / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects; D011817:Rabbits
D015220:Calcium Channels; D007328:Insulin; D015221:Potassium Channels; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; D016257:Fura-2; D017275:Isradipine