Calmodulin Modulates the Delay Period between Release of Calcium from Internal Stores and Activation of Calcium Influx via Endogenous TRP1 Channels

Abstract

In the present study we have explored the role of calmodulin (CaM) and inositol 1,4,5-trisphosphate receptor (IP 3 R) in the communication process activated after the release of calcium from the endoplasmic reticulum (ER) and the activation of calcium influx via endogenous TRP1 channels from Chinese hamster ovary cells. Experiments using combined rapid confocal calcium and electrophysiology measurements uncovered a consistent delay of around 900 ms between the first detectable calcium released from the ER and the activation of the calcium current. This delay was evident with two different methods used to release calcium from the ER: either the blockade of the microsomal calcium ATPase with thapsigargin or activation of bradykinin receptors linked to the IP 3 cascade. Direct application of IP 3 or a peptide from the NH 2 -terminal region of the IP 3 R activated store operated calcium, reducing the delay period. Introduction of CaM into the cell via the patch pipette increased the delay period from 900 ؎ 100 ms to 10 ؎ 2.1 s (n ‫؍‬ 18). Furthermore, the use of selective CaM antagonists W7 and trifluoperazine maleate resulted in a substantial reduction of the delay period to 200 ؎ 100 ms with 5 M trifluoperazine maleate (n ‫؍‬ 16) and 150 ؎ 50 ms with 500 nM W7 (n ‫؍‬ 22). CaM reduced also the current density activated by thapsigargin or brandykinin to about 60% from control. The CaM antagonists did not affect significantly the current density. The results presented here are consistent with an antagonistic effect of IP 3 R and CaM for the activation of store operated calcium after depletion of the ER. The functional competition between the activating effect of IP 3 R and the inhibiting effect of CaM may modulate the delay period between the release of calcium from the ER and the activation of calcium influx observed in different cells, as well as the amount of current activated after depletion of the ER.In a wide variety of nonexcitable and in many excitable cells, activation of G-protein-coupled receptors initiates a linear sequence of events leading to depletion of intracellular calcium storage compartments (the endoplasmic reticulum, ER) 1 via the production of inositol 1,4,5-trisphosphate (IP 3 ) by phospholipase C, and the subsequent induction of calcium influx from the extracellular space (1).Depletion of the ER appears to be a prerequisite for the activation of calcium influx, because several experimental maneuvers that induce depletion of the ER, such as the introduction of IP 3 into the cell or blockade of the microsomal calcium ATPase with thapsigargin (TG) and other selective blockers, are equally effective activators of calcium influx (1).The activation of calcium influx after store depletion has been termed store-operated calcium entry (SOCE) and appears to be a well preserved mechanism from insects to humans (2). The finding that the transient receptor potential protein (TRP) from the Drosophila photoreceptor encodes a calcium-permeable channel activated after depletion of intracellular calcium stores...

Canonical Transient Receptor Potential 1 Plays a Role in Basic Fibroblast Growth Factor (bFGF)/FGF Receptor-1-Induced Ca2+ Entry and Embryonic Rat Neural Stem Cell Proliferation

“…These and the associated conductance changes were significantly reduced by antisense/TRPC1 treatment and eliminated completely by pharmacological blockers of voltage-independent cation channels. TRPC1 has been proposed to be associated with storeoperated Ca 2ϩ influx Vaca and Sampieri, 2002;Beech et al, 2003). However, the present data do not establish whether TRPC1 mediates store-operated or non-store-operated Ca 2ϩ entry in response to bFGF/FGFR-1 signaling in NSC progeny.…”

Calmodulin and calmodulin-dependent protein kinase II inhibit hormone secretion in human parathyroid adenoma

“…This action has been argued to be unrelated to calmodulin. However, calmodulin was reported to inhibit thapsigargin-induced Ca 2C current (Vaca 1996), interrupt activation of calcium influx through TRPC1 channels (Vaca & Sampieri 2002), and inhibit Ca 2C release from the endoplasmic reticulum in skeletal muscle (Buratti et al 1995). These observations suggest that an increased [Ca 2C ] i induced by calmidazolium, as shown here in human parathyroid adenoma cells, may at least partially be calmodulin dependent.…”

Critical roles of Gi/oproteins and phospholipase C-δ1 in the activation of receptor-operated TRPC4 channels

“…DAGs activate TRPC3/C6/C7 but not TRPC4/C5 (18,19). IP 3 Rs were shown to facilitate activation of all TRPCs by competing with Ca 2+ -calmodulin for binding to the conserved C-terminal calmodulin and IP 3 R-binding (CIRB) site (20)(21)(22)(23). Incidentally, the CIRB site is also critical for the Gα i/o effect on TRPC4 (3).…”