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This Article Full Text Full Text (PDF) All Versions of this Article: 586/5/1379    most recent jphysiol.2007.149294v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Belmonte, S. Articles by Morad, M. PubMed PubMed Citation Articles by Belmonte, S. Articles by Morad, M. Related Collections Cardiovascular

¹ Department of Pharmacology, Georgetown University, Washington, DC 20007, USA

Cardiac myocytes, in the intact heart, are exposed to shear/fluid forces during each cardiac cycle. Here we describe a novel Ca²⁺ signalling pathway, generated by ‘pressurized flows’ (PFs) of solutions, resulting in the activation of slowly developing (300 ms) Ca²⁺ transients lasting 1700 ms at room temperature. Though subsequent PFs (applied some 10–30 s later) produced much smaller or undetectable responses, such transients could be reactivated following caffeine- or KCl-induced Ca²⁺ releases, suggesting that a small, but replenishable, Ca²⁺ pool serves as the source for their activation. PF-triggered Ca²⁺ transients could be activated in Ca²⁺-free solutions or in solutions that block voltage-gated Ca²⁺ channels, stretch-activated channels (SACs), or the Na⁺–Ca²⁺ exchanger (NCX), using Cd²⁺, Gd³⁺, or Ni²⁺, respectively. PF-triggered Ca²⁺ transients were significantly smaller in quiescent than in electrically paced myocytes. Paced Ca²⁺ transients activated at the peak of PF-triggered Ca²⁺ transients were not significantly smaller than those produced normally, suggesting functionally separate Ca²⁺ pools for paced and PF-triggered transients. Suppression of nitric oxide (NO) or IP₃ signalling pathways did not alter the PF-triggered Ca²⁺ transients. On the other hand, mitochondrial metabolic uncoupler FCCP, in the presence of oligomycin (to prevent ATP depletion), reversibly suppressed PF-triggered Ca²⁺ transients, as did the mitochondrial Ca²⁺ uniporter (mCU) blocker, Ru360. Reducing agent DTT and reactive oxygen species (ROS) scavenger tempol, as well as mitochondrial NCX (mNCX) blocker CGP-37157, inhibited PF-triggered Ca²⁺ transients. In rhod-2 AM-loaded and permeabilized cells, confocal imaging of mitochondrial Ca²⁺ showed a transient increase in Ca²⁺ on caffeine exposure and a decrease in mitochondrial Ca²⁺ on application of PF pulses of solution. These signals were strongly suppressed by either Na⁺-free or CGP-37157-containing solutions, implicating mNCX in mediating the Ca²⁺ release process. We conclude that subjecting rat cardiac myocytes to pressurized flow pulses of solutions triggers the release of Ca²⁺ from a store that appears to access mitochondrial Ca²⁺.

(Received 4 December 2007; accepted after revision 22 December 2007; first published online 10 January 2008)
Corresponding author M. Morad: Georgetown University, Department of Pharmacology, 4000 Reservoir Road, NW, Washington, DC 20007, USA. Email: moradm{at}georgetown.edu