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

The spatial distribution of Ca 2+ signalling 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.