Effects of CoA and acyl-CoAs on GTP-dependent Ca2+ release and vesicle fusion in rat liver microsomal vesicles

Abstract

(1) CoA (IC50 23 microM) and acyl-CoAs (IC50 values 15-18 microM) inhibit GTP-dependent vesicle fusion in rat liver microsomal vesicles. Acyl-CoAs of carbon chain length C8 and C20 are much less effective than acyl-CoAs of carbon chain length C14-C18. The effect of CoA is mimicked by dephospho-CoA, but not by desulpho-CoA. High acyl-CoA concentrations (50 microM) appear to favour formation of small vesicles (budding), while 50 microM CoA does not. (2) Low concentrations of CoA (EC50 2 microM) and palmitoyl-CoA (10 microM) cause re-accumulation of Ca2+ released in response to GTP. This re-accumulation is into an Ins(1,4,5)P3-sensitive compartment. By investigation of the effects of CoA and palmitoyl-CoA on the thapsigargin-induced passive leak rate of Ca2+, and on the latency of the mannose-6-phosphatase of the vesicles, we conclude that CoA and palmitoyl-CoA cause decreased vesicle permeability rather than stimulation of Ca2+ pumping activity. (3) It is suggested that GTP-induced membrane fusion in rat liver microsomes involves an as yet uncharacterized acylation-deacylation reaction which is required to produce complete vesicle sealing.

Role of long-chain fatty acyl-CoA esters in the regulation of metabolism and in cell signalling

“…values ranging from 15 to 18 µM for C "% -, C "' -and C ") -CoA esters, whereas high acylCoA concentrations (50 µM) favoured the formation of small microsomal vesicles [65]. The authors suggested that GTPinduced membrane fusion in rat liver microsomes depends on an as yet unknown acylation\deacylation mechanism required for complete vesicle sealing.…”

“…In liver, in contrast with muscle, low concentrations of acylCoA suppressed GTP-and inositol 1,4,5-trisphosphate-induced Ca# + release from rat liver microsomal vesicles, and caused re-uptake of Ca# + into and enlargement of the inositol 1,4,5-trisphosphate-sensitive compartment [65,81].…”

Calcium: its modulation in liver by cross-talk between the actions of glucagon and calcium-mobilizing agonists

“…(Benedetti et al, 1988), and therefore a sensitization by glucagon to Ins(1,4,5)P3-dependent agonists can be envisaged. The effect on the Ins(1,4,5)P3-insensitive Ca2+ pool also could contribute to the termination of the effect of Ins(1,4,5)P3-dependent agonists by reaccumulating released Ca2+ (Benedetti et al, 1986 Lee, 1989) and the increase in acyl-CoA cellular content (Comerford and Dawson, 1993 (1985) examining glucagon-induced Ca2+ fluxes in rat hepatocytes was carried out with 24-h-starved animals and the data appear qualitatively similar to those obtained by others using hepatocytes from fed animals. On the other hand, Rashed and Patel (1987) found that in 24-h-fasted animals, glucagon failed to induce 45Ca efflux, but that induced by phenylephrine was unaffected.…”

Fatty Acid-mediated Calcium Sequestration within Intracellular Calcium Pools

“…and that, in a substantially longer period following the GTPinduced interaction, fusion between different vesicular components of the ER may take place (7,16,22,23). Since, in permeabilized cells, a small component of the ER appears to exist as non-intact vesicular membranes, the rapid transfer process induced by GTP results in the fast release of a substantial proportion of the accumulated Ca 2ϩ (7,16), as observed in Fig.…”

“…Work by Comerford and Dawson (22,23) has suggested that GTP-induced Ca 2ϩ movements may reflect the activation of fusion between membranes. Instead, we have interpreted our results to indicate that the rapid fluxes of Ca 2ϩ observed in response to GTP reflect a process that may precede a subsequently activated membrane fusion event (16,24).…”