Adult rat cardiomyocytes exhibit capacitative calcium entry

Abstract

Capacitative Ca(2+) entry (CCE) refers to the influx of Ca(2+) through plasma membrane channels activated on depletion of endoplasmic-sarcoplasmic reticulum Ca(2+) stores. We utilized two Ca(2+)-sensitive dyes (one monitoring cytoplasmic free Ca(2+) and the other free Ca(2+) within the sarcoplasmic reticulum) to determine whether adult rat ventricular myocytes exhibit CCE. Treatments with inhibitors of the sarcoplasmic endoplasmic reticulum Ca(2+)-ATPases were not efficient in releasing Ca(2+) from stores. However, when these inhibitors were coupled with either Ca(2+) 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 Ca(2+) characteristic of CCE. CCE was also observed when stores were depleted with caffeine. This influx of Ca(2+) was sensitive to four inhibitors of CCE (glucosamine, lanthanum, gadolinium, and SKF-96365) but not to inhibitors of L-type channels or the Na(+)/Ca(2+) exchanger. In the whole cell configuration, an inward current of approximately 0.7 pA/pF at -90 mV was activated when a Ca(2+) chelator or inositol (1,4,5)-trisphosphate was included in the pipette or when Ca(2+) stores were depleted with a Ca(2+)-ATPase inhibitor and ionophore. The current was maximal at hyperpolarizing voltages and inwardly rectified. The channel was relatively permeant to Ca(2+) and Ba(2+) but only poorly to Mg(2+) or Mn(2+). 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.