The spatial distribution of Ca(2+) signaling molecules is critical for establishing specific interactions that control Ca(2+) signal generation and transduction. In many cells, close physical coupling of Ca(2+) channels and their targets enables precise and robust activation of effector molecules through local [Ca(2+)]i elevation in microdomains. In T cells, the plasma membrane Ca(2+)-ATPase (PMCA) is a major target of Ca(2+) influx through Ca(2+) release-activated Ca(2+) (CRAC) channels. Elevation of [Ca(2+)]i slowly modulates pump activity to ensure the stability and enhance the dynamic nature of Ca(2+) signals. In this study we probed the functional organization of PMCA and CRAC channels in T cells by manipulating [Ca(2+)] microdomains near CRAC channels and measuring the resultant modulation of PMCAs. The amplitude and spatial extent of microdomains was increased by elevating the rate of Ca(2+) entry, either by raising extracellular [Ca(2+)], by increasing the activity of CRAC channels with 2-aminoethoxyborane (2-APB), or by hyperpolarizing the plasma membrane. Surprisingly, doubling the rate of Ca(2+) influx does not further increase global [Ca(2+)]i in a substantial fraction of cells, due to a compensatory increase in PMCA activity. The enhancement of PMCA activity without changes in global [Ca(2+)]i suggests that local [Ca(2+)]i microdomains near CRAC channels effectively promote PMCA modulation. These results reveal an intimate functional association between CRAC channels and Ca(2+) pumps in the plasma membrane which may play an important role in governing the time course and magnitude of Ca(2+) signals in T cells.
PMID: 14966303 [PubMed - as supplied by publisher]