Mode of mitochondrial Ca2+ clearance and its influence on secretory responses in stimulated chromaffin cells.
To study the role of mitochondrial Ca(2+) clearance in stimulated cells, changes in free Ca(2+) concentration in the cytosol, [Ca(2+)](c) and that in mitochondria, [Ca(2+)](m) along with secretory responses were observed using chromaffin cells co-loaded with Fura-2 and Rhod-2 in the perfused rat adrenal medulla. When the cells were stimulated with 40 mM K(+) in the perfusate, the duration of [Ca(2+)](m) response markedly increased with prolongation of the stimulation period, exhibiting a mean half-decay time of 21 min with 30s stimulation, whereas its amplitude was not altered with stimulations of 10-30s. A computer simulation analysis showed that such a mode of [Ca(2+)](m) response can be produced if excess Ca(2+) taken up by mitochondria precipitates as calcium phosphate (Pi) salt. In the presence of 5 microM rotenone plus 10 microM oligomycin, a decrease in the duration of [Ca(2+)](m) response and a slight but significant increase (24%) in the secretory response to 30s stimulation with 40 mM K(+) were observed. Simulation analyses suggested that this effect of rotenone may be due to reduction in mitochondrial Ca(2+) uptake induced by rotenone-elicited partial depolarization of the mitochondrial membrane potential. In chromaffin cells transsynaptically stimulated through the splanchnic nerve, the intensity of NAD(P)H autofluorescence changed with time courses similar to those of [Ca(2+)](m) responses. The temporal profiles of those two responses were prolonged in a similar manner by application of an inhibitor of mitochondrial Na(+)/Ca(2+) exchanger, CGP37157. Thus, due to the unique Ca(2+) buffering mechanism, [Ca(2+)](m) responses associated with massive mitochondrial Ca(2+) uptake may occur within a limited concentration range in which Ca(2+)-sensitive dehydrogenases are activated to control the mitochondrial redox state in stimulated chromaffin cells.
Warashina
Akira
A
Division of Cell Physiology, Niigata University Graduate School of Medical and Dental Sciences, Niigata 951 8510, Japan. awarashi@med.niigata-u.ac.jp
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002130:Calcium Phosphates / Q000378:metabolism; D019439:Chromaffin Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D003198:Computer Simulation; D003600:Cytosol / Q000378:metabolism; D016257:Fura-2 / Q000494:pharmacology; D006575:Heterocyclic Compounds, 3-Ring / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000502:physiology; D009249:NADP / Q000378:metabolism; D009840:Oligomycins / Q000494:pharmacology; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012402:Rotenone / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors; D013997:Time Factors
D002130:Calcium Phosphates; D006575:Heterocyclic Compounds, 3-Ring; D009840:Oligomycins; D019831:Sodium-Calcium Exchanger; D012402:Rotenone; C068483:rhod-2; D009249:NADP; D010088:Oxidoreductases; D011188:Potassium; D002118:Calcium; D016257:Fura-2