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1 Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL, USA
* To whom correspondence should be addressed. E-mail: marchase{at}uab.edu.
Capacitative Ca2+ entry (CCE) refers to the influx of Ca2+ through plasma membrane channels activated upon depletion of endoplasmic/sarcoplasmic reticulum Ca2+ stores. We utilized two Ca2+-sensitive dyes, one monitoring cytoplasmic free Ca2+ and the other free Ca2+ within the sarcoplasmic reticulum, to determine if adult rat ventricular myocytes exhibit CCE. Treatments with inhibitors of the sarcoplasmic/endoplasmic reticulum Ca2+ATPases were not efficient in releasing Ca2+ from stores. However, when these inhibitors were coupled with either Ca2+ ionophores or angiotensin II, an agonist generating inositol 1,4,5 trisphosphate, depletion of stores was observed. This depletion was accompanied by a significant influx of extracellular Ca2+ characteristic of CCE. CCE was also observed when stores were depleted with caffeine. This influx of Ca2+ was sensitive to four inhibitors of CCE, glucosamine, lanthanum, gadolinium, and SKF 96365, but not to inhibitors of L-type channels or the Na+/Ca2+ exchanger. In the wholecell configuration an inward current of ~0.7pA/pF at -90 mV was activated when a Ca2+ chelator or inositol 1,4,5 trisphosphate was included in the pipette or when Ca2+ stores were depleted with a Ca2+ATPase inhibitor and ionophore. The current was maximal at hyperpolarizing voltages and inwardly rectified. The channel was relatively permeant to Ca2+ and Ba2+ but only poorly to Mg2+ or Mn2+. Taken together, these data support the existence of CCE in adult cardiomyocytes, a finding with likely implications to physiological responses to phospholipase C-generating agonists.
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