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Mitochondrial Ca 2+ homeostasis during Ca 2+ influx and Ca 2+ release in gastric myocytes from Bufo marinus
Author(s) -
Drummond Robert M.,
Mix T. Christian H.,
Tuft Richard A.,
Walsh John V.,
Fay Fredric S.
Publication year - 2000
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2000.t01-2-00375.x
Subject(s) - depolarization , membrane potential , extracellular , endoplasmic reticulum , calcium , biophysics , mitochondrion , myocyte , stimulation , chemistry , cytoplasm , homeostasis , biology , biochemistry , endocrinology , organic chemistry
The Ca 2+ ‐sensitive fluorescent indicator rhod‐2 was used to monitor mitochondrial Ca 2+ concentration ([Ca 2+ ] m ) in gastric smooth muscle cells from Bufo marinus . In some studies, fura‐2 was used in combination with rhod‐2, allowing simultaneous measurement of cytoplasmic Ca 2+ concentration ([Ca 2+ ] i ) and [Ca 2+ ] m , respectively. During a short train of depolarizations, which causes Ca 2+ influx from the extracellular medium, there was an increase in both [Ca 2+ ] i and [Ca 2+ ] m . The half‐time ( t ½ ) to peak for the increase in [Ca 2+ ] m was considerably longer than the t ½ to peak for the increase in [Ca 2+ ] i . [Ca 2+ ] m remained elevated for tens of seconds after [Ca 2+ ] i had returned to its resting value. Stimulation with caffeine, which causes release of Ca 2+ from the sarcoplasmic reticulum (SR), also produced increases in both [Ca 2+ ] i and [Ca 2+ ] m . The values of t ½ to peak for the increase in [Ca 2+ ] in both cytoplasm and mitochondria were similar; however, [Ca 2+ ] i returned to baseline values much faster than [Ca 2+ ] m . Using a wide‐field digital imaging microscope, changes in [Ca 2+ ] m were monitored within individual mitochondria in situ , during stimulation of Ca 2+ influx or Ca 2+ release from the SR. Mitochondrial Ca 2+ uptake during depolarizing stimulation caused depolarization of the mitochondrial membrane potential. The mitochondrial membrane potential recovered considerably faster than the recovery of [Ca 2+ ] m . This study shows that Ca 2+ influx from the extracellular medium and Ca 2+ release from the SR are capable of increasing [Ca 2+ ] m in smooth muscle cells. The efflux of Ca 2+ from the mitochondria is a slow process and appears to be dependent upon the amount of Ca 2+ in the SR.