1995 Fiscal Year Final Research Report Summary
Control of adrenal catecholamine secretion by Ca^<2+> storing mechanisms
| Project/Area Number |
06454121
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Basic veterinary science/Basic zootechnical science
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| Research Institution | HOKKAIDO UNIVERSITY |
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Principal Investigator |
NAKAZATO Yoshikazu Hokkaido University, Graduate School of Vet. Med., Professor, 大学院獣医学研究科, 教授 (60001525)
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| Co-Investigator(Kenkyū-buntansha) |
ITO Shigeo Hokkaido University, Graduate School of Vet. Med., Associate Professor, 大学院獣医学研究科, 助教授 (40109509)
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| Project Period (FY) |
1994 – 1995
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| Keywords | ATP / Adrenal chromaffin cells / Ca influx / GTP analogues / Catecholamine secretion / Ca stores / Na-Ca exhange / Whole cell voltage clamp |
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| Research Abstract |
1. Catecholamine (CA) secretion depending on intracellular Ca store and the effect of extracellular Na : The effect of ryanodine and Ca-ATPase inhibitors on Ca releasing action of caffeine and muscarine from Ca stores was studied in perfused adrenal glands and dispersed chromaffin cells of the quinea pig. In the absence of extracellular Ca, both caffeine and muscarine caused only a small increase in CA secretion which was greatly enhanced after further removal of extracellular Na. Readmission of Ca during perfusion with Na-and Ca-free solution caused inhibition of CA secretion which was reversed to the augmentation by treatment with Ca-ATPase inhibitors.
2. Kinetics of intracellular Ca depending on Ca store and ionic channel activation in single cells : Ryanodine blocked caffeine-induced increase in [Ca]i, but not that induced by muscarine. Inositol 1,4,5, trisphosphate (IP3) and thapsigargin increased[Ca]i and the latter evoked marked inward current. These results suggest that the depletion of intracellular Ca stores in adrenal chromaffin cells may faciliate Ca influx and thus CA secretion through some unknown mechanism as found in smooth muscle cells.
3. Effect of ATP on Ca currents : The effect of ATP on membrane currents was investigated using whole cell voltage clamp techniques. ATP evoked inward current through non-selective cation channels and inhibited Ca currents evoked by depolarizing pulses. The inhibitory effect was abolished by dialysis with GTP analogues. These results suggest that ATP-induced increase in [Ca]i inhibits voltage dependent Ca influx through a mechanism coupled to G protein.
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