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Effects of divalent cations on exocytosis and endocytosis from single mouse pancreatic beta‐cells.
Author(s) -
Proks P,
Ashcroft F M
Publication year - 1995
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 - 10.1113/jphysiol.1995.sp020893
Subject(s) - exocytosis , divalent , depolarization , egta , endocytosis , biophysics , chemistry , intracellular , cytochalasin d , cytochalasin b , secretion , calcium , biochemistry , biology , cell , cytoskeleton , organic chemistry
1. The effects of the divalent cations Ca2+, Ba2+ and Sr2+ on exocytosis and endocytosis from single isolated mouse pancreatic beta‐cells were investigated by monitoring changes in cell capacitance. 2. The immediate increase in capacitance elicited by a single depolarization from ‐70 to +20 mV was dependent on the divalent cation species, with Ca2+ (8.2 +/‐ 1.1 fF pC‐1) > Ba2+ (1.0 +/‐ 0.2 fF pC‐1) > Sr2+ (0.7 +/‐ 0.2 fF pC‐1) in perforated‐patch recordings. 3. In Ba2+ solutions alone there was subsequently an additional slow increase in capacitance (to 4.3 +/‐ 1.1 fF pC‐1). This second phase of exocytosis was unaffected by preincubation with colcemid (20 microM, 45 min) or cytochalasin D (10 microM, 15 min), suggesting that interaction of secretory granules with microtubules or microfilaments is not involved. 4. An increase in cell capacitance was elicited by depolarization in Ba2+ solutions when intracellular Ca2+ was buffered with 10 mM EGTA. Infusion of the beta‐cell with Ba2+ also stimulated exocytosis although the rate was much slower (1.1 +/‐ 0.2 fF s‐1; 8 microM free Ba2+) than for Ca2+ (39 +/‐ 5 fF s‐1; 2 microM free Ca2+). These data indicate that Ba2+ does not evoke secretion by promoting Ca2+ release from internal stores. 5. The lower efficacy of Ba2+ in supporting exocytosis may be related to the fact that this cation does not activate calmodulin‐dependent processes and the slow second phase of secretion may result from this ion being removed only slowly from the cytoplasm. 6. Endocytosis was faster in Sr2+ than in Ca2+ or Ba2+ solution, and the speed increased when the external concentration of all three divalent cation species was raised. The ability of Ba2+ to support endocytosis suggests calmodulin‐dependent processes are not involved. These data suggest membrane retrieval is regulated differently from exocytosis in beta‐cells.