Calcium influx evoked by Ca2+ store depletion in human platelets is more susceptible to cytochrome P-450 inhibitors than receptor-mediated calcium entry

Cell Calcium. 1992 Oct;13(9):553-64. doi: 10.1016/0143-4160(92)90035-q.

Abstract

We have previously reported that a component of ADP-evoked Ca2+ entry in human platelets appears to be promoted following the release of Ca2+ from intracellular stores. Other agonists may employ a similar mechanism. Here we have further investigated the relationship between the state of filling of the Ca2+ stores and plasma membrane Ca2+ permeability in Fura-2-loaded human platelets. Ca2+ influx was promoted following store depletion by inhibitors of the endoplasmic reticulum Ca(2+)-ATPase, thapsigargin (TG) and 2,5-di-(t-butyl)-1,4-benzohydroquinone (tBuBHQ). Divalent cation entry was confirmed by quenching of Fura-2 fluorescence with externally added Mn2+. It has been suggested that cytochrome P-450 may couple Ca2+ store depletion to an increased plasma membrane Ca2+ permeability. In apparent agreement with this, Mn2+ influx promoted by TG and tBuBHQ, or by preincubation of cells in Ca(2+)-free medium, was inhibited by the imidazole antimycotics, econazole and miconazole, which inhibit cytochrome P-450 activity. Agonist-evoked Mn2+ influx was only partially inhibited by these compounds at the same concentration (3 microM). Econazole (3 microM) reduced the Mn2+ quench evoked by ADP by 38% of the control value and that evoked by vasopressin, platelet activating factor (PAF) and thrombin no more than 15% of control, 20 s after agonist addition. Stopped-flow fluorimetry indicated that econazole had no detectable effect on the early time course of agonist-evoked Mn2+ entry or rises in [Ca2+]i. These data confirm the existence of a Ca2+ entry pathway in human platelets which is activated by depletion of the intracellular Ca2+ stores. Further, the results support the suggestion that cytochrome P-450 may participate in such a pathway. However, any physiological role for the cytochrome or its products in agonist-evoked events appears to be in the long-term maintenance or restoration of store Ca2+ content, rather than in promoting Ca2+ influx in the initial stages of platelet Ca2+ signal generation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Diphosphate / pharmacology
  • Blood Platelets / drug effects
  • Blood Platelets / enzymology
  • Blood Platelets / metabolism*
  • Calcium / metabolism*
  • Calcium Channels / drug effects*
  • Calcium Channels / metabolism
  • Calcium Channels / physiology
  • Calcium-Transporting ATPases / antagonists & inhibitors
  • Cell Compartmentation
  • Cytochrome P-450 Enzyme Inhibitors
  • Cytochrome P-450 Enzyme System / physiology*
  • Econazole / pharmacology
  • Humans
  • Hydroquinones / pharmacology
  • Inositol 1,4,5-Trisphosphate / physiology
  • Intracellular Fluid / metabolism
  • Ion Channel Gating / drug effects*
  • Manganese / metabolism
  • Miconazole / pharmacology
  • Osmolar Concentration
  • Platelet Activating Factor / pharmacology
  • Platelet Activation / drug effects
  • Receptors, Cholinergic / physiology
  • Ryanodine Receptor Calcium Release Channel
  • Signal Transduction
  • Terpenes / pharmacology
  • Thapsigargin
  • Thrombin / pharmacology
  • Vasopressins / pharmacology

Substances

  • Calcium Channels
  • Cytochrome P-450 Enzyme Inhibitors
  • Hydroquinones
  • Platelet Activating Factor
  • Receptors, Cholinergic
  • Ryanodine Receptor Calcium Release Channel
  • Terpenes
  • Vasopressins
  • 2,5-di-tert-butylhydroquinone
  • Manganese
  • Adenosine Diphosphate
  • Thapsigargin
  • Econazole
  • Miconazole
  • Inositol 1,4,5-Trisphosphate
  • Cytochrome P-450 Enzyme System
  • Thrombin
  • Calcium-Transporting ATPases
  • Calcium