Cytoplasmic calcium transients due to single action potentials and voltage-clamp depolarizations in mouse pancreatic B-cells.
Changes in the cytoplasmic free calcium concentration ([Ca2+]i) in pancreatic B-cells play an important role in the regulation of insulin secretion. We have recorded [Ca2+]i transients evoked by single action potentials and voltage-clamp Ca2+ currents in isolated B-cells by the combination of dual wavelength emission spectrofluorimetry and the patch-clamp technique. A 500-1000 ms depolarization of the B-cell from -70 to -10 mV evoked a transient rise in [Ca2+]i from a resting value of approximately 100 nM to a peak concentration of 550 nM. Similar [Ca2+]i changes were associated with individual action potentials. The depolarization-induced [Ca2+]i transients were abolished by application of nifedipine, a blocker of L-type Ca2+ channels, indicating their dependence on influx of extracellular Ca2+. Following the voltage-clamp step, [Ca2+]i decayed with a time constant of approximately 2.5 s and summation of [Ca2+]i occurred whenever depolarizations were applied with an interval of less than 2 s. The importance of the Na(+)-Ca2+ exchange for B-cell [Ca2+]i maintenance was evidenced by the demonstration that basal [Ca2+]i rose to 200 nM and the magnitude of the depolarization-evoked [Ca2+]i transients was markedly increased after omission of extracellular Na+. However, the rate by which [Ca2+]i returned to basal was not affected, suggesting the existence of additional [Ca2+]i buffering processes.
Rorsman
P
P
Department of Medical Biophysics, Gothenburg University, Sweden.
Ammälä
C
C
Berggren
P O
PO
Bokvist
K
K
Larsson
O
O
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D007211:Indoles; D007515:Islets of Langerhans / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D009543:Nifedipine / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger; D013050:Spectrometry, Fluorescence
D002352:Carrier Proteins; D005456:Fluorescent Dyes; D007211:Indoles; D008565:Membrane Proteins; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D009543:Nifedipine; C048960:indo-1; D002118:Calcium