Garcia-Barrado, Maria José
Gilon, Patrick
[UCL]
Sato, Yoshihiko
Nenquin, Myriam
[UCL]
Henquin, Jean-Claude
[UCL]
We studied whether reverse Na(+)-Ca2+ exchange can increase cytoplasmic Ca2+ ([Ca2+]i) in mouse islets and contribute to insulin release. The exchange was stimulated by replacing Na+ with choline, sucrose, or lithium in a medium containing 15 mM glucose. Na+ omission increased electrical activity in B cells, [Ca2+]i, and insulin release. When voltage-dependent Ca2+ channels were blocked by nimodipine or closed by holding the membrane polarized with diazoxide, Na+ omission caused a slight hyperpolarization, a small rise in [Ca2+]i, and a marginal increase in insulin release (the latter only with choline). This small rise in [Ca2+]i was dependent on extracellular Ca2+ but was hardly augmented when intracellular Na+ was raised with alanine. When B cells were depolarized by 30 mM K+, Na+ omission did not affect the membrane potential but increased [Ca2+]i and insulin release. If Ca2+ channels were blocked by nimodipine, only marginal increases in Ca2+ and insulin release persisted, which were not different from those observed when the cells were not depolarized. This indicates that Ca2+ influx through voltage-dependent Ca2+ channels rather than via reverse Na(+)-Ca2+ exchange underlies the rise in [Ca2+]i and in insulin release produced by Na+ removal. No decisive support for Ca2+ influx by reverse Na(+)-Ca2+ exchange could be found.
Bibliographic reference |
Garcia-Barrado, Maria José ; Gilon, Patrick ; Sato, Yoshihiko ; Nenquin, Myriam ; Henquin, Jean-Claude. No evidence for a role of reverse Na(+)-Ca2+ exchange in insulin release from mouse pancreatic islets. In: American journal of physiology, Vol. 271, no. 3 Pt 1, p. E426-433 (1996) |
Permanent URL |
http://hdl.handle.net/2078.1/13237 |