Abstract
Regulation of insulin release, membrane potential, transmembrane 45Ca fluxes and cytoplasmic free Ca2+ concentration, [Ca2+](i) was examined using suspension of transplantable NEDH rat insulinoma cells previously cultured for 2-3 days to eliminate necrotic tumour cells and counter prior hypoglycaemia. Insulinoma cells displayed a resting [Ca2+](i) of 94 ± 8 nM (n = 17) and released 104 ± 15 ng insulin 10-6 cells (n = 7) during 60 min incubation with uptake of 2.7 ± 0.2 nmol 45Ca 10-6 cells (n = 7). High concentrations of glucose did not affect membrane potential, transmembrane 45Ca fluxes [Ca2+](i) or insulin release by insulinoma cells. K+ at 25 mM depolarised the plasma membrane, induced a small increase in 45Ca efflux and increased [Ca2+](i) by 65%. This model action was not associated with demonstrable effects on 45Ca uptake and insulin release. The effect of 25 mM K+ on [Ca2+](i) was counteracted by D-600, but this blocker of voltage-activated Ca2+ channels and verapamil lacked effects on transmembrane 45Ca fluxes and insulin release. The Ca2+-calmodulin antagonist, trifluoroperazine, was also without effect on 45Ca fluxes and insulin release. Ca2+ ionophore ionomycin increased [Ca2+](i), whereas A23187 and X537A did not affect transmembrane 45Ca fluxes. Moreover, insulin release was independent of extracellular Ca2+ over the range 0-20.4 mM despite marked affects on transmembrane 45Ca fluxes and a greater than 4-fold change of [Ca2+](i). Dibutyryl cyclic AMP increased insulin release by 55% without affecting transmembrane 45Ca fluxes or [Ca2+](i). The phosphodiesterase inhibitor, theophylline, also enhanced insulin release by 10-36% with no change of 45Ca uptake. The effectiveness of theophylline was independent of extracellular Ca2+ over the range 0-10.2 mM. These results indicate that inappropriate Ca2+ regulation is a key pathogenic feature underlying the inappropriate insulin secretion of rat insulinoma cells.
| Original language | English |
|---|---|
| Pages (from-to) | 22-29 |
| Number of pages | 8 |
| Journal | British Journal of Cancer |
| Volume | 58 |
| Issue number | 1 |
| State | Published - Jan 1 1988 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Cancer Research
- Oncology
Cite this
Measurements of membrane potential, transmembrane 45Ca fluxes, cytoplasmic free Ca2+ concentration and insulin release by transplantable rat insulinoma cells maintained in tissue culture. / Flatt, P. R.; Abrahamsson, H.; Arkhammar, P.; Berggren, P. O.; Rorsman, P.; Swanston-Flatt, S. K.
In: British Journal of Cancer, Vol. 58, No. 1, 01.01.1988, p. 22-29.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Measurements of membrane potential, transmembrane 45Ca fluxes, cytoplasmic free Ca2+ concentration and insulin release by transplantable rat insulinoma cells maintained in tissue culture
AU - Flatt, P. R.
AU - Abrahamsson, H.
AU - Arkhammar, P.
AU - Berggren, P. O.
AU - Rorsman, P.
AU - Swanston-Flatt, S. K.
PY - 1988/1/1
Y1 - 1988/1/1
N2 - Regulation of insulin release, membrane potential, transmembrane 45Ca fluxes and cytoplasmic free Ca2+ concentration, [Ca2+](i) was examined using suspension of transplantable NEDH rat insulinoma cells previously cultured for 2-3 days to eliminate necrotic tumour cells and counter prior hypoglycaemia. Insulinoma cells displayed a resting [Ca2+](i) of 94 ± 8 nM (n = 17) and released 104 ± 15 ng insulin 10-6 cells (n = 7) during 60 min incubation with uptake of 2.7 ± 0.2 nmol 45Ca 10-6 cells (n = 7). High concentrations of glucose did not affect membrane potential, transmembrane 45Ca fluxes [Ca2+](i) or insulin release by insulinoma cells. K+ at 25 mM depolarised the plasma membrane, induced a small increase in 45Ca efflux and increased [Ca2+](i) by 65%. This model action was not associated with demonstrable effects on 45Ca uptake and insulin release. The effect of 25 mM K+ on [Ca2+](i) was counteracted by D-600, but this blocker of voltage-activated Ca2+ channels and verapamil lacked effects on transmembrane 45Ca fluxes and insulin release. The Ca2+-calmodulin antagonist, trifluoroperazine, was also without effect on 45Ca fluxes and insulin release. Ca2+ ionophore ionomycin increased [Ca2+](i), whereas A23187 and X537A did not affect transmembrane 45Ca fluxes. Moreover, insulin release was independent of extracellular Ca2+ over the range 0-20.4 mM despite marked affects on transmembrane 45Ca fluxes and a greater than 4-fold change of [Ca2+](i). Dibutyryl cyclic AMP increased insulin release by 55% without affecting transmembrane 45Ca fluxes or [Ca2+](i). The phosphodiesterase inhibitor, theophylline, also enhanced insulin release by 10-36% with no change of 45Ca uptake. The effectiveness of theophylline was independent of extracellular Ca2+ over the range 0-10.2 mM. These results indicate that inappropriate Ca2+ regulation is a key pathogenic feature underlying the inappropriate insulin secretion of rat insulinoma cells.
AB - Regulation of insulin release, membrane potential, transmembrane 45Ca fluxes and cytoplasmic free Ca2+ concentration, [Ca2+](i) was examined using suspension of transplantable NEDH rat insulinoma cells previously cultured for 2-3 days to eliminate necrotic tumour cells and counter prior hypoglycaemia. Insulinoma cells displayed a resting [Ca2+](i) of 94 ± 8 nM (n = 17) and released 104 ± 15 ng insulin 10-6 cells (n = 7) during 60 min incubation with uptake of 2.7 ± 0.2 nmol 45Ca 10-6 cells (n = 7). High concentrations of glucose did not affect membrane potential, transmembrane 45Ca fluxes [Ca2+](i) or insulin release by insulinoma cells. K+ at 25 mM depolarised the plasma membrane, induced a small increase in 45Ca efflux and increased [Ca2+](i) by 65%. This model action was not associated with demonstrable effects on 45Ca uptake and insulin release. The effect of 25 mM K+ on [Ca2+](i) was counteracted by D-600, but this blocker of voltage-activated Ca2+ channels and verapamil lacked effects on transmembrane 45Ca fluxes and insulin release. The Ca2+-calmodulin antagonist, trifluoroperazine, was also without effect on 45Ca fluxes and insulin release. Ca2+ ionophore ionomycin increased [Ca2+](i), whereas A23187 and X537A did not affect transmembrane 45Ca fluxes. Moreover, insulin release was independent of extracellular Ca2+ over the range 0-20.4 mM despite marked affects on transmembrane 45Ca fluxes and a greater than 4-fold change of [Ca2+](i). Dibutyryl cyclic AMP increased insulin release by 55% without affecting transmembrane 45Ca fluxes or [Ca2+](i). The phosphodiesterase inhibitor, theophylline, also enhanced insulin release by 10-36% with no change of 45Ca uptake. The effectiveness of theophylline was independent of extracellular Ca2+ over the range 0-10.2 mM. These results indicate that inappropriate Ca2+ regulation is a key pathogenic feature underlying the inappropriate insulin secretion of rat insulinoma cells.
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M3 - Article
C2 - 2844219
AN - SCOPUS:0023687231
VL - 58
SP - 22
EP - 29
JO - British Journal of Cancer
JF - British Journal of Cancer
SN - 0007-0920
IS - 1
ER -