FUNCTIONAL POOLS OF GRANULES IN B-CELLS WITHIN INTACT MOUSE PANCREATIC ISLETS OF LANGERHANS

FUNCTIONAL POOLS OF GRANULES IN B-CELLS WITHIN INTACT MOUSE PANCREATIC ISLETS OF LANGERHANS

Field: Other

Authors: Eliasson, Lena
Galvanovskis, Juris
Göpel, Sven
Kanno, Takahiro
Rorsman, Patrik

Address of presenting
author: Department of Physiological Sciences
Sölvegatan 19
223 62 LUND

E-mail: Lena.Eliasson@mphy.lu.se

Phone: +46 46 2220635

Fax: +46 46 2227763

Text of abstract: Transmission electron microscopy (EM) and measurements of cell capacitance on intact islets were combined to determine the correlation between the functional responses and the ultrastructure of the B-cell. Under control conditions the exocytotic response elicited by a 250 ms depolarisation from –70 mV to zero in a B-cell within an intact islet averaged 51±9 fF (n=13). This is twice as large (P=0.05) as the response observed in a single B-cells under the otherwise identical conditions. Forskolin, a known stimulator of exocytosis in single B-cells was unable to stimulate exocytosis elicited by a 500 ms depolarisation. However, when stimulation consisted of a train of nine 500 ms depolarising pulses, forskolin potentiated exocytosis and the total capacitance increase during the train was 580±120 fF (n=4) compared with 340±50 fF (n=9; P<0.05) for the control. These data suggest that B-cells within intact islets are tonically stimulated by glucagon released from neighbouring A-cells already under control conditions and that this act by increasing the size of the releasable pools of granules. Increasing the duration of the depolarising command (from 5 ms to 850 ms) enabled us to determine the size of the immediately releasable pool (IRP). IRP was thus determined to contain no more than 20 secretory granules which may be released within 100 ms. Using EM a 40% reduction in the number of docked granules was observed the islets had been exposed to 75 mM KCl in the absence of glucose (to avoid refilling from the reserve pool). This suggests that part of the reserve pool is situated at the plasma membrane and only needs chemical modification and not translocation prior to insulin release.

Keywords: B-cell, exocytosis, cAMP, capacitance measurements, EM

	FUNCTIONAL POOLS OF GRANULES IN B-CELLS WITHIN INTACT MOUSE PANCREATIC ISLETS OF LANGERHANS
Field:	Other
Authors:	Eliasson, Lena Galvanovskis, Juris Göpel, Sven Kanno, Takahiro Rorsman, Patrik
Address of presenting author:	Department of Physiological Sciences Sölvegatan 19 223 62 LUND
E-mail:	Lena.Eliasson@mphy.lu.se
Phone:	+46 46 2220635
Fax:	+46 46 2227763
Text of abstract:	Transmission electron microscopy (EM) and measurements of cell capacitance on intact islets were combined to determine the correlation between the functional responses and the ultrastructure of the B-cell. Under control conditions the exocytotic response elicited by a 250 ms depolarisation from –70 mV to zero in a B-cell within an intact islet averaged 51±9 fF (n=13). This is twice as large (P=0.05) as the response observed in a single B-cells under the otherwise identical conditions. Forskolin, a known stimulator of exocytosis in single B-cells was unable to stimulate exocytosis elicited by a 500 ms depolarisation. However, when stimulation consisted of a train of nine 500 ms depolarising pulses, forskolin potentiated exocytosis and the total capacitance increase during the train was 580±120 fF (n=4) compared with 340±50 fF (n=9; P<0.05) for the control. These data suggest that B-cells within intact islets are tonically stimulated by glucagon released from neighbouring A-cells already under control conditions and that this act by increasing the size of the releasable pools of granules. Increasing the duration of the depolarising command (from 5 ms to 850 ms) enabled us to determine the size of the immediately releasable pool (IRP). IRP was thus determined to contain no more than 20 secretory granules which may be released within 100 ms. Using EM a 40% reduction in the number of docked granules was observed the islets had been exposed to 75 mM KCl in the absence of glucose (to avoid refilling from the reserve pool). This suggests that part of the reserve pool is situated at the plasma membrane and only needs chemical modification and not translocation prior to insulin release.

Keywords:	B-cell, exocytosis, cAMP, capacitance measurements, EM

Index

Created 2000-03-15

Department of Physiological Sciences, Lund University

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