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Capacitance measurements of exocytosis in mouse pancreatic α‐, β‐ and δ‐cells within intact islets of Langerhans
Author(s) -
Göpel Sven,
Zhang Quan,
Eliasson Lena,
Ma XiaoSong,
Galvanovskis Juris,
Kanno Takahiro,
Salehi Albert,
Rorsman Patrik
Publication year - 2004
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.2003.059675
Subject(s) - exocytosis , glucagon , channel blocker , nifedipine , depolarization , endocrinology , medicine , biophysics , chemistry , patch clamp , pancreatic islets , somatostatin , membrane potential , secretion , islet , electrophysiology , insulin , biology , calcium
Capacitance measurements of exocytosis were applied to functionally identified α‐, β‐ and δ‐cells in intact mouse pancreatic islets. The maximum rate of capacitance increase in β‐cells during a depolarization to 0 mV was equivalent to 14 granules s −1 , <5% of that observed in isolated β‐cells. β‐Cell secretion exhibited bell‐shaped voltage dependence and peaked at +20 mV. At physiological membrane potentials (up to ∼−20 mV) the maximum rate of release was ∼4 granules s −1 . Both exocytosis (measured by capacitance measurements) and insulin release (detected by radioimmunoassay) were strongly inhibited by the L‐type Ca 2+ channel blocker nifedipine (25 μ m ) but only marginally (<20%) affected by the R‐type Ca 2+ channel blocker SNX482 (100 n m ). Exocytosis in the glucagon‐producing α‐cells peaked at +20 mV. The capacitance increases elicited by pulses to 0 mV exhibited biphasic kinetics and consisted of an initial transient (150 granules s −1 ) and a sustained late component (30 granules s −1 ). Whereas addition of the N‐type Ca 2+ channel blocker ω‐conotoxin GVIA (0.1 μ m ) inhibited glucagon secretion measured in the presence of 1 m m glucose to the same extent as an elevation of glucose to 20 m m , the L‐type Ca 2+ channel blocker nifedipine (25 μ m ) had no effect. Thus, glucagon release during hyperglycaemic conditions depends principally on Ca 2+ ‐influx through N‐type rather than L‐type Ca 2+ channels. Exocytosis in the somatostatin‐secreting δ‐cells likewise exhibited two kinetically separable phases of capacitance increase and consisted of an early rapid (600 granules s −1 ) component followed by a sustained slower (60 granules s −1 ) component. We conclude that (1) capacitance measurements in intact pancreatic islets are feasible; (2) exocytosis measured in β‐cells in situ is significantly slower than that of isolated cells; and (3) the different types of islet cells exhibit distinct exocytotic features.