L-type Ca2+ channel desensitization by F- reduces PhE-induced increase in [Ca2+]i but not stress.
F- (10 mM sodium fluoride plus deferoxamine to chelate contaminating aluminum) causes arterial contractions primarily by activating L-type Ca2+ channels. Results from the present study indicate that, although F(-)-induced contractions could be completely relaxed by washing out the F- with fresh buffer, a long-lasting effect of F- pretreatment was to produce L-type Ca2+ channel desensitization. Pretreatment of arteries for 4 h with F- (followed by washout of F-) resulted in much reduced increases in stress and [Ca2+]i produced by the subsequent addition of 110 mM KCl, such that steady-state values were, respectively, only 9 and 15% of the control values. However, a 4-h F- pretreatment caused a reduction only in the rate of stress development, but not the steady-state level of stress, produced by maximum concentrations of receptor agonists. In tissues that were pretreated with F- and then stimulated with the alpha-adrenoceptor agonist, phenylephrine, steady-state stress was still 104% of the control value, while the increase in [Ca2+]i was only 10% of the control value. F- is known to inhibit protein phosphatases, and similar reductions in the ability of KCl to produce contractions and increase [Ca2+]i were seen after pretreatment with the protein phosphatase inhibitor, okadaic acid. These data suggest that L-type Ca2+ channel desensitization by F- pretreatment was caused by increased protein phosphorylation. In addition, they suggest that much of the contribution made by L-type Ca2+ channels to increase [Ca2+]i during receptor stimulation may not be necessary for the maintenance of maximum stress at steady state.
Department of Pharmacology, Eastern Virginia Medical School, Norfolk 23501.
P H
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Ratz
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Lattanzio
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D003676:Deferoxamine / Q000494:pharmacology; D015237:Dinoprost / Q000494:pharmacology; D005260:Female; D005263:Femoral Artery / Q000502:physiology; D005459:Fluorides / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D010656:Phenylephrine / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D013314:Stress, Mechanical; D013997:Time Factors
D015220:Calcium Channels; D010656:Phenylephrine; D011189:Potassium Chloride; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D015237:Dinoprost; D003676:Deferoxamine; D005459:Fluorides; D002118:Calcium