Vasorelaxation and inhibition of the voltage‐operated Ca²⁺ channels by FK506 in the porcine coronary artery

Abstract

1 Using fura-2¯uorometry, the e ects of FK506, an immunosuppressant, on changes in cytosolic Ca 2+ concentrations ([Ca 2+ ] i ) and tension were investigated in porcine coronary arterial strips. The e ects of FK506 on the activity of voltage-operated Ca 2+ channels were examined by applying a whole cell patch clamp to the isolated smooth muscle cells of porcine coronary artery. 2 FK506 inhibited the sustained increases in both [Ca 2+ ] i and tension induced by 118 mM K + depolarization and 100 nM U46619 in a concentration-dependent manner (1 ± 30 mM). The extent of inhibition of the K + -induced contraction was greater than that of the U46619-induced contraction. The increases in [Ca 2+ ] i and tension induced by histamine and endothelin-1 in the presence of extracellular Ca 2+ were also inhibited by 10 mM FK506. 3 FK506 (10 mM) had no e ect on Ca 2+ release induced by ca eine or by histamine in the Ca 2+ -free solution. 4 FK506 (10 mM) had no e ect on the [Ca 2+ ] i -tension relationships of the contractions induced by cumulative increases of extracellular Ca 2+ during K + depolarization or stimulation with U46619. 5 In the patch clamp experiments, FK506 (30 mM) partially inhibited the inward current induced by depolarization pulse from 780 mV to 0 mV. 6 In conclusion, FK506 induces arterial relaxation by decreasing [Ca 2+ ] i mainly due to the inhibition of the L-type Ca 2+ channels, with no e ect on the Ca 2+ sensitivity of the contractile apparatus.

Binding of rapamycin analogs to calcium channels and FKBP52 contributes to their neuroprotective activities

“…A 49% decrease of the Ca 2ϩ current density (6.5 Ϯ 0.5 to 3.2 Ϯ 0.3 pA/pF) was observed after incubation of WYE-592 (data not shown), similar to that observed for FK506, as has been reported (20). The effect of WYE-592 on L-type VGCC also was studied in F-11 cells by intracellular application of WYE-592.…”

Pharmacology of inositol trisphosphate receptors

“…Similarly to other macrocyclic compounds (ivermectin, rapamycin and ascomycin), FK506 concentrations higher than 10 M also inhibited the Ca 2+ pumps of the sarco-and endoplasmic reticulum [13,24]. High FK506 concentrations (10-50 M) also affected voltage-operated Ca 2+ channels in the porcine coronary artery [191] and voltage-operated Ca 2+ channeldependent long-term potentiation in the hippocampus [128]. They had no effect on the passive Ca 2+ leak from the stores, but as reported for other lipophilic compounds, the washing out of FK506 transiently increased this leak [27].…”

The 12 kDa FK506-binding protein, FKBP12, modulates the Ca2+-flux properties of the type-3 ryanodine receptor

“…This is compatible with previous findings showing that in the presence of the immunosuppressant FK506, which disrupts FKBP12 interaction, RyR1 and RyR2 channels become more sensitive to activators, such as caffeine, Ca 2+ or ATP (Timerman et al, 1993;Brillantes et al, 1994;Mayrleitner et al, 1994;Ondrias et al, 1998;Gaburjakova et al, 2001). The use of FK506, however, must be viewed with caution, since this drug has multiple effects on intracellular Ca 2+ homeostasis independent of RyRs (Bultynck et al, 2003), including effects on the sarcoand endoplasmic reticulum Ca 2+ -ATPases (Bultynck et al, 2000;Bilmen et al, 2002), the passive Ca 2+ leak (Bultynck et al, 2002), Ca 2+ -influx channels (Burley and Sihra, 2000), voltage-operated Ca 2+ channels (Yasutsune et al, 1999), Ca 2+ -activated K + channels (Terashima et al, 1998) and the outward K + current (duBell et al, 1997). Disruption of FKBP12 interaction with wt RyR3 by FK506 treatment led, in our hands, to non-specific effects (data not shown), probably related to Ca 2+ -pump inhibition (Bultynck et al, 2000) and to effects of the solvent ethanol on the activation of RyR3 channels (Table 1).…”