Palmitate increases L-type Ca2+ currents and the size of the readily releasable granule pool in mouse pancreatic beta-cells.
We have investigated the in vitro effects of the saturated free fatty acid palmitate on mouse pancreatic beta-cells by a combination of electrophysiological recordings, intracellular Ca(2+) ([Ca(2+)](i)) microfluorimetry and insulin release measurements. Addition of palmitate (1 mm, bound to fatty acid-free albumin) to intact islets exposed to 15 mm glucose increased the [Ca(2+)](i) by approximately 30% and insulin secretion 2-fold. Palmitate remained capable of increasing [Ca(2+)](i) and insulin release in the presence of tolbutamide and in islets depolarized by high K(+) in combination with diazoxide, indicating that the stimulation occurs independently of closure of ATP-regulated K(+) channels (K(ATP) channels). Palmitate (0.5 mm) augmented exocytosis (measured as an increase in cell capacitance) in single beta-cells and increased the size of the readily releasable pool (RRP) of granules 2-fold. Whole-cell peak Ca(2+) currents rose by approximately 25% following addition of 0.5 mm palmitate, an effect that was abolished in the presence of 10 microm isradipine indicating that the free fatty acid specifically acts on L-type Ca(2+) channels. The actions of palmitate on exocytosis and Ca(2+) currents were not mimicked by intracellular application of palmitoyl-CoA. We conclude that palmitate increases insulin secretion by a K(ATP) channel-independent mechanism exerted at the level of exocytosis and that involves both augmentation of L-type Ca(2+) currents and an increased size of the RRP.
Olofsson
Charlotta S
CS
Department of Physiological Sciences, Lund University, Sweden. charlotta.olofsson@mphy.lu.se
Salehi
Albert
A
Holm
Cecilia
C
Rorsman
Patrik
P
D018528:ATP-Binding Cassette Transporters; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D016764:Cell Polarity / Q000187:drug effects; D002469:Cell Separation; D048429:Cell Size; D000242:Cyclic AMP / Q000502:physiology; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism*; D004594:Electrophysiology; D005089:Exocytosis / Q000187:drug effects; D005260:Female; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism*; D054086:KATP Channels; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D010168:Palmitates / Q000494:pharmacology*; D010171:Palmitoyl Coenzyme A / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying; D012710:Serum Albumin, Bovine / Q000494:pharmacology
D018528:ATP-Binding Cassette Transporters; D020746:Calcium Channels, L-Type; D007328:Insulin; D054086:KATP Channels; D010168:Palmitates; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; C092520:uK-ATP-1 potassium channel; D010171:Palmitoyl Coenzyme A; D012710:Serum Albumin, Bovine; D000242:Cyclic AMP; D005947:Glucose; D002118:Calcium