Caffeine exerts a dual effect on capacitative calcium entry in Xenopus oocytes

Caffeine increases the amplitude of the Cl- currents evoked by capacitative Ca2+ entry (CCE) on thapsigargin-treated Xenopus oocytes. The caffeine-ind uced potentiation of the CCE process appears to rest on two distinct and ad ditive components. The first component involves the cAMP second messenger s ystem since it can be mimicked by either IBMX perfusion or cAMP microinject ion into the oocyte and inhibited by the PKA inhibitory peptide i-PKA. The second component, although activatory, is dynamically related to the caffei ne-evoked inhibition of InsP(3)-mediated Ca2+ release and may arise from an interaction between caffeine and the InsP(3) receptor in the context of a conformational coupling between the InsP(3) receptor and the channels respo nsible for CCE. (C) 2000 Elsevier Science Inc, All rights reserved.