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Alterations in calcium metabolism in phorbol ester-treated mouse peritoneal macrophages
Abstract:
Phorbol 12-myristate 13-acetate (PMA)-treated macrophages exhibited a two-fold increase in the rate of 45Ca++ efflux and over a three-fold increase in the size of the exchangeable calcium pool, resulting in almost a seven-fold increase in the slow phase of calcium efflux. The calcium antagonist 8-(N,N-diethylamino) octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) by itself did not affect calcium efflux in macrophages; but abolished the PMA-induced increase in the rate of calcium efflux. The divalent cationphore A23187 increased the rate constant of the fast phase of calcium efflux two-fold when applied alone or when applied with PMA. These effects might be linked to ionophore enhancement and TMB-8 inhibition of PMA-induced macrophage chemotaxis and spreading (previously reported in Cell Calcium 3:503-514 and Cancer Research 43:3385-3391). No change in calcium efflux was observed if cells were exposed to PMA only during the efflux experiment suggesting that a prolonged exposure to PMA is required to elicit changes in calcium flux. Increased 45Ca++ remained in treated cells at each time point perhaps reflecting the PMA-induced increase in exchangeable calcium.
Insights
Phorbol 12-myristate 13-acetate (PMA) significantly increases calcium (Ca++) efflux and pool size in macrophages. The calcium antagonist TMB-8 blocks PMA
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Macrophages play crucial roles in immune responses.
- Calcium homeostasis is vital for cellular functions.
- Phorbol esters are known to modulate cell behavior.
Purpose of the Study:
- To investigate the effects of PMA on calcium efflux and pool size in macrophages.
- To determine the role of calcium flux in PMA-induced macrophage activation.
- To examine the modulatory effects of TMB-8 and A23187 on calcium dynamics.
Main Methods:
- Macrophage cell cultures were treated with PMA.
- 45Ca++ efflux and exchangeable calcium pool size were measured.
- The effects of TMB-8 and the ionophore A23187 were assessed.
Main Results:
- PMA treatment doubled 45Ca++ efflux rate and tripled exchangeable calcium pool size.
- TMB-8 inhibited PMA-induced calcium efflux.
- A23187 enhanced calcium efflux, with or without PMA.
Conclusions:
- PMA alters macrophage calcium flux, increasing efflux and pool size.
- TMB-8 antagonizes PMA's effects on calcium efflux.
- Prolonged PMA exposure is necessary for these calcium flux alterations.