Relative contribution of the Na(+)/Ca(2+) exchanger, mitochondria and endoplasmic reticulum in the regulation of cytosolic Ca(2+) and catecholamine secretion of bovine adrenal chromaffin cells.
The relative importance of mitochondria, the Na(+)/Ca(2+) exchanger (NCX) and the endoplasmic reticulum (ER) in the regulation of the cytosolic Ca(2+) concentration ([Ca(2+)](i)) were examined in bovine chromaffin cells using fura-2 for average [Ca(2+)](i) and amperometry for secretory activity, which reflects the local Ca(2+) concentration near the exocytotic sites. Chromaffin cells were stimulated by a high concentration of K(+) when the three Ca(2+) removal mechanisms were individually or simultaneously inhibited. When the mitochondrial Ca(2+) uptake was inhibited, the [Ca(2+)](i) decayed at a significantly slower rate and the secretory activity was higher than the control cells. The NCX appears to function only in the initial phase of [Ca(2+)](i) decay and when the ER Ca(2+) pump is blocked. Similarly, the ER had a significant effect on the [Ca(2+)](i) decay and on the secretion only when the NCX was blocked. Inhibition of all three mechanisms leads to a substantial delay in [Ca(2+)](i) recovery and an increase in the secretion. The results suggest that the three mechanisms work together in the regulation of the Ca(2+) near the Ca(2+) channels and exocytotic sites and therefore modulate the secretory activity. When Ca(2+) diffuses away from the exocytotic sites, the mitochondrial Ca(2+) uptake becomes the dominant mechanism.
Yang
D M
DM
Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan, China.
Kao
L S
LS
D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004563:Electrochemistry; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology; D005456:Fluorescent Dyes; D016257:Fura-2; D007476:Ionophores / Q000494:pharmacology; D008536:Meglumine / Q000378:metabolism / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*
D015220:Calcium Channels; D002395:Catecholamines; D005456:Fluorescent Dyes; D007476:Ionophores; D019831:Sodium-Calcium Exchanger; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D008536:Meglumine; D012964:Sodium; D011188:Potassium; D002118:Calcium; D016257:Fura-2