Modulation of plasma membrane calcium-ATPase activity by local calcium microdomains near CRAC channels in human T cells

The spatial distribution of Ca2+ signalling molecules is critical for establishing specific interactions that control Ca2+ signal generation and transduction. In many cells, close physical coupling of Ca2+ channels and their targets enables precise and robust activation of effector molecules through local [Ca2+](i) elevation in microdomains. In T cells, the plasma membrane Ca2+-ATPase (PMCA) is a major target of Ca2+ influx through Ca2+ release-activated Ca2+ (CRAC) channels. Elevation of [Ca2+](i) slowly modulates pump activity to ensure the stability and enhance the dynamic nature of Ca2+ signals. In this study we probed the functional organization of PMCA and CRAC channels in T cells by manipulating Ca2+ 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 Ca2+ entry, either by raising extracellular [Ca2+], by increasing the activity of CRAC channels with 2-aminoethoxyborane (2-APB), or by hyperpolarizing the plasma membrane. Surprisingly, doubling the rate of Ca2+ influx does not further increase global [Ca2+], in a substantial fraction of cells, due to a compensatory increase in PMCA activity. The enhancement of PMCA activity without changes in global [Ca2+](i) suggests that local [Ca2+], microdomains near CRAC channels effectively promote PMCA modulation. These results reveal an intimate functional association between CRAC channels and Ca2+ pumps in the plasma membrane which may play an important role in governing the time course and magnitude of Ca2+ signals in T cells.