Effects of caffeine on intracellular calcium release and calcium influx in a clonal beta-cell line RINm5F.
We studied the effects of caffeine on intracellular calcium in a clonal insulin-secreting cell line RINm5F. Caffeine (1-30 mM) induced a dose-dependent intracellular Ca2+ release and Ca2+ influx. Pretreatment with combination of ryanodine (10 microM) and caffeine (10 mM), but not ryanodine alone, abolished subsequent caffeine-induced release of intracellular Ca2+. Pretreatment with another ryanodine receptor blocker procaine (0.1, 0.3, and 1mM) antagonized the caffeine-induced release of intracellular Ca2+. Pretreatment with thapsigargin (2 microM), the endoplasmic reticular Ca2+-ATPase inhibitor, abolished both the caffeine- and arginine vasopressin (AVP)-induced Ca2+ release. AVP induces Ca2+ release by increasing the formation of IP3. Pretreatment with AVP greatly reduced caffeine-induced Ca2+ release whereas pretreatment with caffeine also reduced AVP-induced Ca2+ release. The L-type Ca2+ channel blocker nimodipine (1 microM) inhibited caffeine-induced Ca2+ influx. In addition, depletion of intracellular Ca2+ stores with thapsigargin did not affect caffeine-induced Ca2+ influx. These results suggested that: 1) the ryanodine- and caffeine-sensitive Ca2+ store exists in RINm5F cells, 2) most of these Ca2+ release channels in RINm5F cells are closed in the resting state, since pretreatment with ryanodine alone failed to block the caffeine-induced Ca2+ release, 3) there is a "cross-talk" between the caffeine- and IP3-sensitive pools in RINm5F cells, 4) caffeine increases Ca2+ entry in RINm5F cells through L-type voltage-dependent Ca2+ channels, and 5) the caffeine-induced Ca2+ influx is independent of the Ca2+ release from the intracellular Ca2+ stores.
Chen
T H
TH
Department of Veterinary Physiology and Pharmacology, Iowa State University, Ames, 50011, USA.
Lee
B
B
Yang
C
C
Hsu
W H
WH
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D009553:Nimodipine / Q000494:pharmacology; D010179:Pancreas / Q000187:drug effects; D011343:Procaine / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology
D012433:Ryanodine; D002110:Caffeine; D011343:Procaine; D009553:Nimodipine; D002118:Calcium