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-, ß- and 
-cells within intact islets of Langerhans
Department of Physiological Sciences, BMC F11, SE-221 84 Lund, Sweden
Capacitance measurements of exocytosis were applied to functionally identified 
-, ß- and 
-cells in intact mouse pancreatic islets. The maximum rate of capacitance increase in ß-cells during a depolarization to 0 mV was equivalent to 14 granules s–1, <5% of that observed in isolated ß-cells. ß-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 Ca2+ channel blocker nifedipine (25 µM) but only marginally (<20%) affected by the R-type Ca2+ channel blocker SNX482 (100 nM). Exocytosis in the glucagon-producing -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 Ca2+ channel blocker 
-conotoxin GVIA (0.1 µM) inhibited glucagon secretion measured in the presence of 1 mM glucose to the same extent as an elevation of glucose to 20 mM, the L-type Ca2+ channel blocker nifedipine (25 µM) had no effect. Thus, glucagon release during hyperglycaemic conditions depends principally on Ca2+-influx through N-type rather than L-type Ca2+ channels. Exocytosis in the somatostatin-secreting -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 ß-cells in situ is significantly slower than that of isolated cells; and (3) the different types of islet cells exhibit distinct exocytotic features.
(Received 14 December 2003;
accepted after revision 6 February 2004;
first published online 13 February 2004)
Corresponding author P. Rorsman: Diabetes Research Laboratory, The Oxford Centre for Diabetes, Endocrinology and Metabolism, The Churchill Hospital, Oxford OX3 7LJ, UK. Email: patrik.rorsman{at}drl.ox.ac.uk
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